Pre-decode instructions when writing them to icache

This splits out the decoding done in the decode0 step into a separate
predecoder, used when writing instructions into the icache.  The
icache now holds 36 bits per instruction rather than 32.  For valid
instructions, those 36 bits comprise the bottom 26 bits of the
instruction word, a 9-bit insn_code value (which uniquely identifies
the instruction), and a zero in the MSB.  For illegal instructions,
the MSB is one and the full instruction word is in the bottom 32 bits.
Having the full instruction word available for illegal instructions
means that it can be printed in the log when simulating, or in future
could be placed in the HEIR register.

If we don't have an FPU, then the floating-point instructions are
regarded as illegal.  In that case, the insn_code values would fit
into 8 bits, which could be used in future to reduce the size of
decode_rom from 512 to 256 entries.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
pull/382/head
Paul Mackerras 2 years ago
parent 26dc1e879c
commit 21ab36a0c0

@ -56,7 +56,7 @@ all = core_tb icache_tb dcache_tb dmi_dtm_tb \
all: $(all)

core_files = decode_types.vhdl common.vhdl wishbone_types.vhdl fetch1.vhdl \
utils.vhdl plru.vhdl cache_ram.vhdl icache.vhdl \
utils.vhdl plru.vhdl cache_ram.vhdl icache.vhdl predecode.vhdl \
decode1.vhdl helpers.vhdl insn_helpers.vhdl \
control.vhdl decode2.vhdl register_file.vhdl \
cr_file.vhdl crhelpers.vhdl ppc_fx_insns.vhdl rotator.vhdl \

@ -7,6 +7,7 @@ entity cache_ram is
generic(
ROW_BITS : integer := 16;
WIDTH : integer := 64;
BYTEWID : integer := 8;
TRACE : boolean := false;
ADD_BUF : boolean := false
);
@ -16,7 +17,7 @@ entity cache_ram is
rd_en : in std_logic;
rd_addr : in std_logic_vector(ROW_BITS - 1 downto 0);
rd_data : out std_logic_vector(WIDTH - 1 downto 0);
wr_sel : in std_logic_vector(WIDTH/8 - 1 downto 0);
wr_sel : in std_logic_vector(WIDTH/BYTEWID - 1 downto 0);
wr_addr : in std_logic_vector(ROW_BITS - 1 downto 0);
wr_data : in std_logic_vector(WIDTH - 1 downto 0)
);
@ -38,7 +39,7 @@ begin
variable lbit : integer range 0 to WIDTH - 1;
variable mbit : integer range 0 to WIDTH - 1;
variable widx : integer range 0 to SIZE - 1;
constant sel0 : std_logic_vector(WIDTH/8 - 1 downto 0)
constant sel0 : std_logic_vector(WIDTH/BYTEWID - 1 downto 0)
:= (others => '0');
begin
if rising_edge(clk) then
@ -49,9 +50,9 @@ begin
" dat:" & to_hstring(wr_data);
end if;
end if;
for i in 0 to WIDTH/8-1 loop
lbit := i * 8;
mbit := lbit + 7;
for i in 0 to WIDTH/BYTEWID-1 loop
lbit := i * BYTEWID;
mbit := lbit + BYTEWID - 1;
widx := to_integer(unsigned(wr_addr));
if wr_sel(i) = '1' then
ram(widx)(mbit downto lbit) <= wr_data(mbit downto lbit);

@ -246,12 +246,13 @@ package common is
fetch_failed: std_ulogic;
nia: std_ulogic_vector(63 downto 0);
insn: std_ulogic_vector(31 downto 0);
icode: insn_code;
big_endian: std_ulogic;
next_predicted: std_ulogic;
next_pred_ntaken: std_ulogic;
end record;
constant IcacheToDecode1Init : IcacheToDecode1Type :=
(nia => (others => '0'), insn => (others => '0'), others => '0');
(nia => (others => '0'), insn => (others => '0'), icode => INSN_illegal, others => '0');

type IcacheEventType is record
icache_miss : std_ulogic;

@ -246,6 +246,7 @@ begin
icache_0: entity work.icache
generic map(
SIM => SIM,
HAS_FPU => HAS_FPU,
LINE_SIZE => 64,
NUM_LINES => ICACHE_NUM_LINES,
NUM_WAYS => ICACHE_NUM_WAYS,

@ -31,22 +31,6 @@ entity decode1 is
end entity decode1;

architecture behaviour of decode1 is
type dc0_t is record
f_in : IcacheToDecode1Type;
use_row : std_ulogic;
br_pred : std_ulogic;
override : std_ulogic;
ov_insn : insn_code;
spr_info : spr_id;
ram_spr : ram_spr_info;
end record;
constant dc0_t_init : dc0_t :=
(f_in => IcacheToDecode1Init, ov_insn => INSN_illegal,
spr_info => spr_id_init, ram_spr => ram_spr_info_init,
others => '0');

signal dc0, dc0in : dc0_t;

signal r, rin : Decode1ToDecode2Type;
signal f, fin : Decode1ToFetch1Type;

@ -58,437 +42,10 @@ architecture behaviour of decode1 is

signal br, br_in : br_predictor_t;

signal maj_rom_addr : std_ulogic_vector(10 downto 0);
signal row_rom_addr : std_ulogic_vector(10 downto 0);
signal major_predecode : insn_code;
signal row_predecode : insn_code;

signal decode_rom_addr : insn_code;
signal decode : decode_rom_t;
signal rom_ce : std_ulogic;

type predecoder_rom_t is array(0 to 2047) of insn_code;

constant major_predecode_rom : predecoder_rom_t := (
2#001100_00000# to 2#001100_11111# => INSN_addic,
2#001101_00000# to 2#001101_11111# => INSN_addic_dot,
2#001110_00000# to 2#001110_11111# => INSN_addi,
2#001111_00000# to 2#001111_11111# => INSN_addis,
2#010011_00100# to 2#010011_00101# => INSN_addpcis,
2#011100_00000# to 2#011100_11111# => INSN_andi_dot,
2#011101_00000# to 2#011101_11111# => INSN_andis_dot,
2#000000_00000# => INSN_attn,
2#010010_00000# to 2#010010_11111# => INSN_b,
2#010000_00000# to 2#010000_11111# => INSN_bc,
2#001011_00000# to 2#001011_11111# => INSN_cmpi,
2#001010_00000# to 2#001010_11111# => INSN_cmpli,
2#100010_00000# to 2#100010_11111# => INSN_lbz,
2#100011_00000# to 2#100011_11111# => INSN_lbzu,
2#110010_00000# to 2#110010_11111# => INSN_lfd,
2#110011_00000# to 2#110011_11111# => INSN_lfdu,
2#110000_00000# to 2#110000_11111# => INSN_lfs,
2#110001_00000# to 2#110001_11111# => INSN_lfsu,
2#101010_00000# to 2#101010_11111# => INSN_lha,
2#101011_00000# to 2#101011_11111# => INSN_lhau,
2#101000_00000# to 2#101000_11111# => INSN_lhz,
2#101001_00000# to 2#101001_11111# => INSN_lhzu,
2#100000_00000# to 2#100000_11111# => INSN_lwz,
2#100001_00000# to 2#100001_11111# => INSN_lwzu,
2#000111_00000# to 2#000111_11111# => INSN_mulli,
2#011000_00000# to 2#011000_11111# => INSN_ori,
2#011001_00000# to 2#011001_11111# => INSN_oris,
2#010100_00000# to 2#010100_11111# => INSN_rlwimi,
2#010101_00000# to 2#010101_11111# => INSN_rlwinm,
2#010111_00000# to 2#010111_11111# => INSN_rlwnm,
2#010001_00000# to 2#010001_11111# => INSN_sc,
2#100110_00000# to 2#100110_11111# => INSN_stb,
2#100111_00000# to 2#100111_11111# => INSN_stbu,
2#110110_00000# to 2#110110_11111# => INSN_stfd,
2#110111_00000# to 2#110111_11111# => INSN_stfdu,
2#110100_00000# to 2#110100_11111# => INSN_stfs,
2#110101_00000# to 2#110101_11111# => INSN_stfsu,
2#101100_00000# to 2#101100_11111# => INSN_sth,
2#101101_00000# to 2#101101_11111# => INSN_sthu,
2#100100_00000# to 2#100100_11111# => INSN_stw,
2#100101_00000# to 2#100101_11111# => INSN_stwu,
2#001000_00000# to 2#001000_11111# => INSN_subfic,
2#000010_00000# to 2#000010_11111# => INSN_tdi,
2#000011_00000# to 2#000011_11111# => INSN_twi,
2#011010_00000# to 2#011010_11111# => INSN_xori,
2#011011_00000# to 2#011011_11111# => INSN_xoris,
-- major opcode 4
2#000100_10000# => INSN_maddhd,
2#000100_10001# => INSN_maddhdu,
2#000100_10011# => INSN_maddld,
-- major opcode 30
2#011110_01000# to 2#011110_01001# => INSN_rldic,
2#011110_01010# to 2#011110_01011# => INSN_rldic,
2#011110_00000# to 2#011110_00001# => INSN_rldicl,
2#011110_00010# to 2#011110_00011# => INSN_rldicl,
2#011110_00100# to 2#011110_00101# => INSN_rldicr,
2#011110_00110# to 2#011110_00111# => INSN_rldicr,
2#011110_01100# to 2#011110_01101# => INSN_rldimi,
2#011110_01110# to 2#011110_01111# => INSN_rldimi,
2#011110_10000# to 2#011110_10001# => INSN_rldcl,
2#011110_10010# to 2#011110_10011# => INSN_rldcr,
-- major opcode 58
2#111010_00000# => INSN_ld,
2#111010_00001# => INSN_ldu,
2#111010_00010# => INSN_lwa,
2#111010_00100# => INSN_ld,
2#111010_00101# => INSN_ldu,
2#111010_00110# => INSN_lwa,
2#111010_01000# => INSN_ld,
2#111010_01001# => INSN_ldu,
2#111010_01010# => INSN_lwa,
2#111010_01100# => INSN_ld,
2#111010_01101# => INSN_ldu,
2#111010_01110# => INSN_lwa,
2#111010_10000# => INSN_ld,
2#111010_10001# => INSN_ldu,
2#111010_10010# => INSN_lwa,
2#111010_10100# => INSN_ld,
2#111010_10101# => INSN_ldu,
2#111010_10110# => INSN_lwa,
2#111010_11000# => INSN_ld,
2#111010_11001# => INSN_ldu,
2#111010_11010# => INSN_lwa,
2#111010_11100# => INSN_ld,
2#111010_11101# => INSN_ldu,
2#111010_11110# => INSN_lwa,
-- major opcode 59
2#111011_00100# to 2#111011_00101# => INSN_fdivs,
2#111011_01000# to 2#111011_01001# => INSN_fsubs,
2#111011_01010# to 2#111011_01011# => INSN_fadds,
2#111011_01100# to 2#111011_01101# => INSN_fsqrts,
2#111011_10000# to 2#111011_10001# => INSN_fres,
2#111011_10010# to 2#111011_10011# => INSN_fmuls,
2#111011_10100# to 2#111011_10101# => INSN_frsqrtes,
2#111011_11000# to 2#111011_11001# => INSN_fmsubs,
2#111011_11010# to 2#111011_11011# => INSN_fmadds,
2#111011_11100# to 2#111011_11101# => INSN_fnmsubs,
2#111011_11110# to 2#111011_11111# => INSN_fnmadds,
-- major opcode 62
2#111110_00000# => INSN_std,
2#111110_00001# => INSN_stdu,
2#111110_00100# => INSN_std,
2#111110_00101# => INSN_stdu,
2#111110_01000# => INSN_std,
2#111110_01001# => INSN_stdu,
2#111110_01100# => INSN_std,
2#111110_01101# => INSN_stdu,
2#111110_10000# => INSN_std,
2#111110_10001# => INSN_stdu,
2#111110_10100# => INSN_std,
2#111110_10101# => INSN_stdu,
2#111110_11000# => INSN_std,
2#111110_11001# => INSN_stdu,
2#111110_11100# => INSN_std,
2#111110_11101# => INSN_stdu,
-- major opcode 63
2#111111_00100# to 2#111111_00101# => INSN_fdiv,
2#111111_01000# to 2#111111_01001# => INSN_fsub,
2#111111_01010# to 2#111111_01011# => INSN_fadd,
2#111111_01100# to 2#111111_01101# => INSN_fsqrt,
2#111111_01110# to 2#111111_01111# => INSN_fsel,
2#111111_10000# to 2#111111_10001# => INSN_fre,
2#111111_10010# to 2#111111_10011# => INSN_fmul,
2#111111_10100# to 2#111111_10101# => INSN_frsqrte,
2#111111_11000# to 2#111111_11001# => INSN_fmsub,
2#111111_11010# to 2#111111_11011# => INSN_fmadd,
2#111111_11100# to 2#111111_11101# => INSN_fnmsub,
2#111111_11110# to 2#111111_11111# => INSN_fnmadd,
others => INSN_illegal
);

constant row_predecode_rom : predecoder_rom_t := (
-- Major opcode 31
-- Address bits are 0, insn(10:1)
2#0_01000_01010# => INSN_add,
2#0_11000_01010# => INSN_add, -- addo
2#0_00000_01010# => INSN_addc,
2#0_10000_01010# => INSN_addc, -- addco
2#0_00100_01010# => INSN_adde,
2#0_10100_01010# => INSN_adde, -- addeo
2#0_00101_01010# => INSN_addex,
2#0_00010_01010# => INSN_addg6s,
2#0_00111_01010# => INSN_addme,
2#0_10111_01010# => INSN_addme, -- addmeo
2#0_00110_01010# => INSN_addze,
2#0_10110_01010# => INSN_addze, -- addzeo
2#0_00000_11100# => INSN_and,
2#0_00001_11100# => INSN_andc,
2#0_00111_11100# => INSN_bperm,
2#0_01001_11010# => INSN_cbcdtd,
2#0_01000_11010# => INSN_cdtbcd,
2#0_00000_00000# => INSN_cmp,
2#0_01111_11100# => INSN_cmpb,
2#0_00111_00000# => INSN_cmpeqb,
2#0_00001_00000# => INSN_cmpl,
2#0_00110_00000# => INSN_cmprb,
2#0_00001_11010# => INSN_cntlzd,
2#0_00000_11010# => INSN_cntlzw,
2#0_10001_11010# => INSN_cnttzd,
2#0_10000_11010# => INSN_cnttzw,
2#0_10111_10011# => INSN_darn,
2#0_00010_10110# => INSN_dcbf,
2#0_00001_10110# => INSN_dcbst,
2#0_01000_10110# => INSN_dcbt,
2#0_00111_10110# => INSN_dcbtst,
2#0_11111_10110# => INSN_dcbz,
2#0_01100_01001# => INSN_divdeu,
2#0_11100_01001# => INSN_divdeu, -- divdeuo
2#0_01100_01011# => INSN_divweu,
2#0_11100_01011# => INSN_divweu, -- divweuo
2#0_01101_01001# => INSN_divde,
2#0_11101_01001# => INSN_divde, -- divdeo
2#0_01101_01011# => INSN_divwe,
2#0_11101_01011# => INSN_divwe, -- divweo
2#0_01110_01001# => INSN_divdu,
2#0_11110_01001# => INSN_divdu, -- divduo
2#0_01110_01011# => INSN_divwu,
2#0_11110_01011# => INSN_divwu, -- divwuo
2#0_01111_01001# => INSN_divd,
2#0_11111_01001# => INSN_divd, -- divdo
2#0_01111_01011# => INSN_divw,
2#0_11111_01011# => INSN_divw, -- divwo
2#0_11001_10110# => INSN_nop, -- dss
2#0_01010_10110# => INSN_nop, -- dst
2#0_01011_10110# => INSN_nop, -- dstst
2#0_11010_10110# => INSN_eieio,
2#0_01000_11100# => INSN_eqv,
2#0_11101_11010# => INSN_extsb,
2#0_11100_11010# => INSN_extsh,
2#0_11110_11010# => INSN_extsw,
2#0_11011_11010# => INSN_extswsli,
2#0_11011_11011# => INSN_extswsli,
2#0_11110_10110# => INSN_icbi,
2#0_00000_10110# => INSN_icbt,
2#0_00000_01111# => INSN_isel,
2#0_00001_01111# => INSN_isel,
2#0_00010_01111# => INSN_isel,
2#0_00011_01111# => INSN_isel,
2#0_00100_01111# => INSN_isel,
2#0_00101_01111# => INSN_isel,
2#0_00110_01111# => INSN_isel,
2#0_00111_01111# => INSN_isel,
2#0_01000_01111# => INSN_isel,
2#0_01001_01111# => INSN_isel,
2#0_01010_01111# => INSN_isel,
2#0_01011_01111# => INSN_isel,
2#0_01100_01111# => INSN_isel,
2#0_01101_01111# => INSN_isel,
2#0_01110_01111# => INSN_isel,
2#0_01111_01111# => INSN_isel,
2#0_10000_01111# => INSN_isel,
2#0_10001_01111# => INSN_isel,
2#0_10010_01111# => INSN_isel,
2#0_10011_01111# => INSN_isel,
2#0_10100_01111# => INSN_isel,
2#0_10101_01111# => INSN_isel,
2#0_10110_01111# => INSN_isel,
2#0_10111_01111# => INSN_isel,
2#0_11000_01111# => INSN_isel,
2#0_11001_01111# => INSN_isel,
2#0_11010_01111# => INSN_isel,
2#0_11011_01111# => INSN_isel,
2#0_11100_01111# => INSN_isel,
2#0_11101_01111# => INSN_isel,
2#0_11110_01111# => INSN_isel,
2#0_11111_01111# => INSN_isel,
2#0_00001_10100# => INSN_lbarx,
2#0_11010_10101# => INSN_lbzcix,
2#0_00011_10111# => INSN_lbzux,
2#0_00010_10111# => INSN_lbzx,
2#0_00010_10100# => INSN_ldarx,
2#0_10000_10100# => INSN_ldbrx,
2#0_11011_10101# => INSN_ldcix,
2#0_00001_10101# => INSN_ldux,
2#0_00000_10101# => INSN_ldx,
2#0_10010_10111# => INSN_lfdx,
2#0_10011_10111# => INSN_lfdux,
2#0_11010_10111# => INSN_lfiwax,
2#0_11011_10111# => INSN_lfiwzx,
2#0_10000_10111# => INSN_lfsx,
2#0_10001_10111# => INSN_lfsux,
2#0_00011_10100# => INSN_lharx,
2#0_01011_10111# => INSN_lhaux,
2#0_01010_10111# => INSN_lhax,
2#0_11000_10110# => INSN_lhbrx,
2#0_11001_10101# => INSN_lhzcix,
2#0_01001_10111# => INSN_lhzux,
2#0_01000_10111# => INSN_lhzx,
2#0_00000_10100# => INSN_lwarx,
2#0_01011_10101# => INSN_lwaux,
2#0_01010_10101# => INSN_lwax,
2#0_10000_10110# => INSN_lwbrx,
2#0_11000_10101# => INSN_lwzcix,
2#0_00001_10111# => INSN_lwzux,
2#0_00000_10111# => INSN_lwzx,
2#0_10010_00000# => INSN_mcrxrx,
2#0_00000_10011# => INSN_mfcr,
2#0_00010_10011# => INSN_mfmsr,
2#0_01010_10011# => INSN_mfspr,
2#0_01000_01001# => INSN_modud,
2#0_01000_01011# => INSN_moduw,
2#0_11000_01001# => INSN_modsd,
2#0_11000_01011# => INSN_modsw,
2#0_00100_10000# => INSN_mtcrf,
2#0_00100_10010# => INSN_mtmsr,
2#0_00101_10010# => INSN_mtmsrd,
2#0_01110_10011# => INSN_mtspr,
2#0_00010_01001# => INSN_mulhd,
2#0_00000_01001# => INSN_mulhdu,
2#0_00010_01011# => INSN_mulhw,
2#0_00000_01011# => INSN_mulhwu,
-- next 4 have reserved bit set
2#0_10010_01001# => INSN_mulhd,
2#0_10000_01001# => INSN_mulhdu,
2#0_10010_01011# => INSN_mulhw,
2#0_10000_01011# => INSN_mulhwu,
2#0_00111_01001# => INSN_mulld,
2#0_10111_01001# => INSN_mulld, -- mulldo
2#0_00111_01011# => INSN_mullw,
2#0_10111_01011# => INSN_mullw, -- mullwo
2#0_01110_11100# => INSN_nand,
2#0_00011_01000# => INSN_neg,
2#0_10011_01000# => INSN_neg, -- nego
-- next 8 are reserved no-op instructions
2#0_10000_10010# => INSN_nop,
2#0_10001_10010# => INSN_nop,
2#0_10010_10010# => INSN_nop,
2#0_10011_10010# => INSN_nop,
2#0_10100_10010# => INSN_nop,
2#0_10101_10010# => INSN_nop,
2#0_10110_10010# => INSN_nop,
2#0_10111_10010# => INSN_nop,
2#0_00011_11100# => INSN_nor,
2#0_01101_11100# => INSN_or,
2#0_01100_11100# => INSN_orc,
2#0_00011_11010# => INSN_popcntb,
2#0_01111_11010# => INSN_popcntd,
2#0_01011_11010# => INSN_popcntw,
2#0_00101_11010# => INSN_prtyd,
2#0_00100_11010# => INSN_prtyw,
2#0_00100_00000# => INSN_setb,
2#0_01111_10010# => INSN_slbia,
2#0_00000_11011# => INSN_sld,
2#0_00000_11000# => INSN_slw,
2#0_11000_11010# => INSN_srad,
2#0_11001_11010# => INSN_sradi,
2#0_11001_11011# => INSN_sradi,
2#0_11000_11000# => INSN_sraw,
2#0_11001_11000# => INSN_srawi,
2#0_10000_11011# => INSN_srd,
2#0_10000_11000# => INSN_srw,
2#0_11110_10101# => INSN_stbcix,
2#0_10101_10110# => INSN_stbcx,
2#0_00111_10111# => INSN_stbux,
2#0_00110_10111# => INSN_stbx,
2#0_10100_10100# => INSN_stdbrx,
2#0_11111_10101# => INSN_stdcix,
2#0_00110_10110# => INSN_stdcx,
2#0_00101_10101# => INSN_stdux,
2#0_00100_10101# => INSN_stdx,
2#0_10110_10111# => INSN_stfdx,
2#0_10111_10111# => INSN_stfdux,
2#0_11110_10111# => INSN_stfiwx,
2#0_10100_10111# => INSN_stfsx,
2#0_10101_10111# => INSN_stfsux,
2#0_11100_10110# => INSN_sthbrx,
2#0_11101_10101# => INSN_sthcix,
2#0_10110_10110# => INSN_sthcx,
2#0_01101_10111# => INSN_sthux,
2#0_01100_10111# => INSN_sthx,
2#0_10100_10110# => INSN_stwbrx,
2#0_11100_10101# => INSN_stwcix,
2#0_00100_10110# => INSN_stwcx,
2#0_00101_10111# => INSN_stwux,
2#0_00100_10111# => INSN_stwx,
2#0_00001_01000# => INSN_subf,
2#0_10001_01000# => INSN_subf, -- subfo
2#0_00000_01000# => INSN_subfc,
2#0_10000_01000# => INSN_subfc, -- subfco
2#0_00100_01000# => INSN_subfe,
2#0_10100_01000# => INSN_subfe, -- subfeo
2#0_00111_01000# => INSN_subfme,
2#0_10111_01000# => INSN_subfme, -- subfmeo
2#0_00110_01000# => INSN_subfze,
2#0_10110_01000# => INSN_subfze, -- subfzeo
2#0_10010_10110# => INSN_sync,
2#0_00010_00100# => INSN_td,
2#0_00000_00100# => INSN_tw,
2#0_01001_10010# => INSN_tlbie,
2#0_01000_10010# => INSN_tlbiel,
2#0_10001_10110# => INSN_tlbsync,
2#0_00000_11110# => INSN_wait,
2#0_01001_11100# => INSN_xor,

-- Major opcode 19
-- Columns with insn(4) = '1' are all illegal and not mapped here; to
-- fit into 2048 entries, the columns are remapped so that 16-24 are
-- stored here as 8-15; in other words the address bits are
-- 1, insn(10..6), 1, insn(5), insn(3..1)
2#1_10000_11000# => INSN_bcctr,
2#1_00000_11000# => INSN_bclr,
2#1_10001_11000# => INSN_bctar,
2#1_01000_10001# => INSN_crand,
2#1_00100_10001# => INSN_crandc,
2#1_01001_10001# => INSN_creqv,
2#1_00111_10001# => INSN_crnand,
2#1_00001_10001# => INSN_crnor,
2#1_01110_10001# => INSN_cror,
2#1_01101_10001# => INSN_crorc,
2#1_00110_10001# => INSN_crxor,
2#1_00100_11110# => INSN_isync,
2#1_00000_10000# => INSN_mcrf,
2#1_00000_11010# => INSN_rfid,

-- Major opcode 59
-- Only column 14 is valid here; columns 16-31 are handled in the major table
-- Column 14 is mapped to column 6 of the space which is
-- mostly used for opcode 19.
2#1_11010_10110# => INSN_fcfids,
2#1_11110_10110# => INSN_fcfidus,

-- Major opcode 63
-- Columns 0-15 are mapped here; columns 16-31 are in the major table.
-- Address bits are 1, insn(10:6), 0, insn(4:1)
2#1_00000_00000# => INSN_fcmpu,
2#1_00001_00000# => INSN_fcmpo,
2#1_00010_00000# => INSN_mcrfs,
2#1_00100_00000# => INSN_ftdiv,
2#1_00101_00000# => INSN_ftsqrt,
2#1_00001_00110# => INSN_mtfsb,
2#1_00010_00110# => INSN_mtfsb,
2#1_00100_00110# => INSN_mtfsfi,
2#1_11010_00110# => INSN_fmrgow,
2#1_11110_00110# => INSN_fmrgew,
2#1_10010_00111# => INSN_mffs,
2#1_10110_00111# => INSN_mtfsf,
2#1_00000_01000# => INSN_fcpsgn,
2#1_00001_01000# => INSN_fneg,
2#1_00010_01000# => INSN_fmr,
2#1_00100_01000# => INSN_fnabs,
2#1_01000_01000# => INSN_fabs,
2#1_01100_01000# => INSN_frin,
2#1_01101_01000# => INSN_friz,
2#1_01110_01000# => INSN_frip,
2#1_01111_01000# => INSN_frim,
2#1_00000_01100# => INSN_frsp,
2#1_00000_01110# => INSN_fctiw,
2#1_00100_01110# => INSN_fctiwu,
2#1_11001_01110# => INSN_fctid,
2#1_11010_01110# => INSN_fcfid,
2#1_11101_01110# => INSN_fctidu,
2#1_11110_01110# => INSN_fcfidu,
2#1_00000_01111# => INSN_fctiwz,
2#1_00100_01111# => INSN_fctiwuz,
2#1_11001_01111# => INSN_fctidz,
2#1_11101_01111# => INSN_fctiduz,

others => INSN_illegal
);
signal fetch_failed : std_ulogic;

-- If we have an FPU, then it is used for integer divisions,
-- otherwise a dedicated divider in the ALU is used.
@ -871,16 +428,18 @@ architecture behaviour of decode1 is
end;

begin
decode0_0: process(clk)
decode1_0: process(clk)
begin
if rising_edge(clk) then
if rst = '1' then
dc0 <= dc0_t_init;
r <= Decode1ToDecode2Init;
fetch_failed <= '0';
elsif flush_in = '1' then
dc0.f_in.valid <= '0';
dc0.f_in.fetch_failed <= '0';
r.valid <= '0';
fetch_failed <= '0';
elsif stall_in = '0' then
dc0 <= dc0in;
r <= rin;
fetch_failed <= f_in.fetch_failed;
end if;
if rst = '1' then
br.br_nia <= (others => '0');
@ -892,139 +451,73 @@ begin
end if;
end process;

decode0_roms: process(clk)
busy_out <= stall_in;

decode1_rom: process(clk)
begin
if rising_edge(clk) then
if stall_in = '0' then
if is_X(maj_rom_addr) then
major_predecode <= INSN_illegal;
else
major_predecode <= major_predecode_rom(to_integer(unsigned(maj_rom_addr)));
end if;
if is_X(row_rom_addr) then
row_predecode <= INSN_illegal;
else
row_predecode <= row_predecode_rom(to_integer(unsigned(row_rom_addr)));
end if;
decode <= decode_rom(decode_rom_addr);
end if;
end if;
end process;

decode0_1: process(all)
variable v : dc0_t;
variable majorop : std_ulogic_vector(5 downto 0);
variable majaddr : std_ulogic_vector(10 downto 0);
variable rowaddr : std_ulogic_vector(10 downto 0);
variable sprn : spr_num_t;
decode1_1: process(all)
variable v : Decode1ToDecode2Type;
variable vr : Decode1ToRegisterFileType;
variable br_target : std_ulogic_vector(61 downto 0);
variable br_offset : signed(23 downto 0);
variable bv : br_predictor_t;
variable icode : insn_code;
variable sprn : spr_num_t;
variable maybe_rb : std_ulogic;
begin
v := dc0_t_init;
v.f_in := f_in;

br_offset := (others => '0');

majorop := f_in.insn(31 downto 26);
majaddr := majorop & f_in.insn(4 downto 0);

-- row_predecode_rom is used for op 19, 31, 59, 63
-- addr bit 10 is 0 for op 31, 1 for 19, 59, 63
rowaddr(10) := f_in.insn(31) or not f_in.insn(29);
rowaddr(9 downto 5) := f_in.insn(10 downto 6);
if f_in.insn(28) = '0' then
-- op 19 and op 59
rowaddr(4 downto 3) := '1' & f_in.insn(5);
else
-- op 31 and 63; for 63 we only use this when f_in.insn(5) = '0'
rowaddr(4 downto 3) := f_in.insn(5 downto 4);
end if;
rowaddr(2 downto 0) := f_in.insn(3 downto 1);
v := Decode1ToDecode2Init;

maj_rom_addr <= majaddr;
row_rom_addr <= rowaddr;
v.valid := f_in.valid;
v.nia := f_in.nia;
v.insn := f_in.insn;
v.stop_mark := f_in.stop_mark;
v.big_endian := f_in.big_endian;

if is_X(f_in.insn) then
v.spr_info := (sel => "XXX", others => 'X');
v.ram_spr := (index => (others => 'X'), others => 'X');
else
sprn := decode_spr_num(f_in.insn);
v.spr_info := map_spr(sprn);
v.ram_spr := decode_ram_spr(sprn);
end if;

case unsigned(majorop) is
when "000100" => -- 4
-- major opcode 4, mostly VMX/VSX stuff but also some integer ops (madd*)
v.override := not f_in.insn(5);

when "011111" => -- 31
-- major opcode 31, lots of things
-- Use the first half of the row table for all columns
v.use_row := '1';

when "010000" => -- 16
-- Predict backward branches as taken, forward as untaken
v.br_pred := f_in.insn(15);
br_offset := resize(signed(f_in.insn(15 downto 2)), 24);

when "010010" => -- 18
-- Unconditional branches are always taken
v.br_pred := '1';
br_offset := signed(f_in.insn(25 downto 2));

when "010011" => -- 19
-- Columns 8-15 and 24-31 don't have any valid instructions
-- (where insn(5..1) is the column number).
-- addpcis (column 2) is in the major table
-- Other valid columns are mapped to columns in the second
-- half of the row table: columns 0-1 are mapped to 16-17
-- and 16-23 are mapped to 24-31.
v.override := f_in.insn(4);
v.use_row := f_in.insn(5) or (not f_in.insn(3) and not f_in.insn(2));

when "011000" => -- 24
-- ori, special-case the standard NOP
if std_match(f_in.insn, "01100000000000000000000000000000") then
v.override := '1';
v.ov_insn := INSN_nop;
end if;

when "111011" => -- 59
if HAS_FPU then
-- floating point operations, mostly single-precision
-- Columns 0-11 are illegal; columns 12-15 are mapped
-- to columns 20-23 in the second half of the row table,
-- and columns 16-31 are in the major table.
v.override := not f_in.insn(5) and (not f_in.insn(4) or not f_in.insn(3));
v.use_row := not f_in.insn(5);
else
v.override := '1';
end if;

when "111111" => -- 63
if HAS_FPU then
-- floating point operations, general and double-precision
-- Use columns 0-15 of the second half of the row table
-- for columns 0-15, and the major table for columns 16-31.
v.use_row := not f_in.insn(5);
else
v.override := '1';
end if;
sprn := decode_spr_num(f_in.insn);
v.spr_info := map_spr(sprn);
v.ram_spr := decode_ram_spr(sprn);
end if;

when others =>
end case;
icode := f_in.icode;

if f_in.fetch_failed = '1' then
v.override := '1';
v.ov_insn := INSN_fetch_fail;
icode := INSN_fetch_fail;
-- Only send down a single OP_FETCH_FAILED
v.f_in.valid := not dc0.f_in.fetch_failed;
v.valid := not fetch_failed;
end if;
decode_rom_addr <= icode;

if f_in.valid = '1' then
report "Decode " & insn_code'image(icode) & " " & to_hstring(f_in.insn) &
" at " & to_hstring(f_in.nia);
end if;

-- Branch predictor
-- Note bclr, bcctr and bctar are predicted not taken as we have no
-- Note bclr, bcctr and bctar not predicted as we have no
-- count cache or link stack.
br_offset := (others => '0');
case icode is
when INSN_b =>
-- Unconditional branches are always taken
v.br_pred := '1';
br_offset := signed(f_in.insn(25 downto 2));
when INSN_bc =>
-- Predict backward branches as taken, forward as untaken
v.br_pred := f_in.insn(15);
br_offset := resize(signed(f_in.insn(15 downto 2)), 24);
when others =>
end case;
bv.br_nia := f_in.nia(63 downto 2);
if f_in.insn(1) = '1' then
bv.br_nia := (others => '0');
@ -1039,80 +532,16 @@ begin
-- after a clock edge...
br_target := std_ulogic_vector(signed(br.br_nia) + br.br_offset);

dc0in <= v;
br_in <= bv;

f_out.redirect <= br.predict;
f_out.redirect_nia <= br_target & "00";
flush_out <= bv.predict or br.predict;
end process;

decode1_0: process(clk)
begin
if rising_edge(clk) then
if rst = '1' then
r <= Decode1ToDecode2Init;
elsif flush_in = '1' then
r.valid <= '0';
elsif stall_in = '0' then
r <= rin;
end if;
end if;
end process;

busy_out <= stall_in;

decode1_rom: process(clk)
begin
if rising_edge(clk) then
if stall_in = '0' then
decode <= decode_rom(decode_rom_addr);
end if;
end if;
end process;

decode1_1: process(all)
variable v : Decode1ToDecode2Type;
variable vr : Decode1ToRegisterFileType;
variable icode : insn_code;
variable sprn : spr_num_t;
variable maybe_rb : std_ulogic;
begin
v := Decode1ToDecode2Init;

v.valid := dc0.f_in.valid;
v.nia := dc0.f_in.nia;
v.insn := dc0.f_in.insn;
v.stop_mark := dc0.f_in.stop_mark;
v.big_endian := dc0.f_in.big_endian;
v.br_pred := dc0.br_pred;
v.spr_info := dc0.spr_info;
v.ram_spr := dc0.ram_spr;

if dc0.override = '1' then
icode := dc0.ov_insn;
elsif dc0.use_row = '0' then
icode := major_predecode;
else
icode := row_predecode;
end if;
decode_rom_addr <= icode;

if dc0.f_in.valid = '1' then
report "Decode insn " & to_hstring(dc0.f_in.insn) & " at " & to_hstring(dc0.f_in.nia) &
" code " & insn_code'image(icode);
end if;

-- Work out GPR/FPR read addresses
maybe_rb := '0';
vr.reg_1_addr := '0' & insn_ra(dc0.f_in.insn);
vr.reg_2_addr := '0' & insn_rb(dc0.f_in.insn);
vr.reg_3_addr := '0' & insn_rs(dc0.f_in.insn);
vr.reg_1_addr := '0' & insn_ra(f_in.insn);
vr.reg_2_addr := '0' & insn_rb(f_in.insn);
vr.reg_3_addr := '0' & insn_rs(f_in.insn);
if icode >= INSN_first_rb then
maybe_rb := '1';
if icode < INSN_first_frs then
if icode >= INSN_first_rc then
vr.reg_3_addr := '0' & insn_rcreg(dc0.f_in.insn);
vr.reg_3_addr := '0' & insn_rcreg(f_in.insn);
end if;
else
-- access FRS operand
@ -1124,13 +553,13 @@ begin
end if;
if icode >= INSN_first_frabc then
-- access FRC operand
vr.reg_3_addr := '1' & insn_rcreg(dc0.f_in.insn);
vr.reg_3_addr := '1' & insn_rcreg(f_in.insn);
end if;
end if;
end if;
vr.read_1_enable := dc0.f_in.valid and not dc0.f_in.fetch_failed;
vr.read_2_enable := dc0.f_in.valid and not dc0.f_in.fetch_failed and maybe_rb;
vr.read_3_enable := dc0.f_in.valid and not dc0.f_in.fetch_failed;
vr.read_1_enable := f_in.valid;
vr.read_2_enable := f_in.valid and maybe_rb;
vr.read_3_enable := f_in.valid;

v.reg_a := vr.reg_1_addr;
v.reg_b := vr.reg_2_addr;
@ -1138,11 +567,15 @@ begin

-- Update registers
rin <= v;
br_in <= bv;

-- Update outputs
d_out <= r;
d_out.decode <= decode;
r_out <= vr;
f_out.redirect <= br.predict;
f_out.redirect_nia <= br_target & "00";
flush_out <= bv.predict or br.predict;
end process;

d1_log: if LOG_LENGTH > 0 generate

@ -23,6 +23,7 @@ use ieee.numeric_std.all;
library work;
use work.utils.all;
use work.common.all;
use work.decode_types.all;
use work.wishbone_types.all;

-- 64 bit direct mapped icache. All instructions are 4B aligned.
@ -30,6 +31,7 @@ use work.wishbone_types.all;
entity icache is
generic (
SIM : boolean := false;
HAS_FPU : boolean := true;
-- Line size in bytes
LINE_SIZE : positive := 64;
-- BRAM organisation: We never access more than wishbone_data_bits at
@ -122,8 +124,20 @@ architecture rtl of icache is
subtype way_t is integer range 0 to NUM_WAYS-1;
subtype row_in_line_t is unsigned(ROW_LINEBITS-1 downto 0);

-- We store a pre-decoded 10-bit insn_code along with the bottom 26 bits of
-- each instruction, giving a total of 36 bits per instruction, which
-- fits neatly into the block RAMs available on FPGAs.
-- For illegal instructions, the top 4 bits are ones and the bottom 6 bits
-- are the instruction's primary opcode, so we have the whole instruction
-- word available (e.g. to put in HEIR). For other instructions, the
-- primary opcode is not stored but could be determined from the insn_code.
constant PREDECODE_BITS : natural := 10;
constant INSN_IMAGE_BITS : natural := 26;
constant ICWORDLEN : natural := PREDECODE_BITS + INSN_IMAGE_BITS;
constant ROW_WIDTH : natural := INSN_PER_ROW * ICWORDLEN;

-- The cache data BRAM organized as described above for each way
subtype cache_row_t is std_ulogic_vector(ROW_SIZE_BITS-1 downto 0);
subtype cache_row_t is std_ulogic_vector(ROW_WIDTH-1 downto 0);

-- The cache tags LUTRAM has a row per set. Vivado is a pain and will
-- not handle a clean (commented) definition of the cache tags as a 3d
@ -184,6 +198,8 @@ architecture rtl of icache is
wb : wishbone_master_out;
store_way : way_t;
store_index : index_t;
recv_row : row_t;
recv_valid : std_ulogic;
store_row : row_t;
store_tag : cache_tag_t;
store_valid : std_ulogic;
@ -214,7 +230,9 @@ architecture rtl of icache is

-- Cache RAM interface
type cache_ram_out_t is array(way_t) of cache_row_t;
signal cache_out : cache_ram_out_t;
signal cache_out : cache_ram_out_t;
signal cache_wr_data : std_ulogic_vector(ROW_WIDTH - 1 downto 0);
signal wb_rd_data : std_ulogic_vector(ROW_SIZE_BITS - 1 downto 0);

-- PLRU output interface
type plru_out_t is array(index_t) of std_ulogic_vector(WAY_BITS-1 downto 0);
@ -293,7 +311,7 @@ architecture rtl of icache is
variable word: integer range 0 to INSN_PER_ROW-1;
begin
word := to_integer(unsigned(addr(INSN_BITS+2-1 downto 2)));
return data(31+word*32 downto word*32);
return data(word * ICWORDLEN + ICWORDLEN - 1 downto word * ICWORDLEN);
end;

-- Get the tag value from the address
@ -327,6 +345,34 @@ architecture rtl of icache is

begin

-- byte-swap read data if big endian
process(all)
variable j: integer;
begin
if r.store_tag(TAG_BITS - 1) = '0' then
wb_rd_data <= wishbone_in.dat;
else
for ii in 0 to (wishbone_in.dat'length / 8) - 1 loop
j := ((ii / 4) * 4) + (3 - (ii mod 4));
wb_rd_data(ii * 8 + 7 downto ii * 8) <= wishbone_in.dat(j * 8 + 7 downto j * 8);
end loop;
end if;
end process;

predecoder_0: entity work.predecoder
generic map (
HAS_FPU => HAS_FPU,
WIDTH => INSN_PER_ROW,
ICODE_LEN => PREDECODE_BITS,
IMAGE_LEN => INSN_IMAGE_BITS
)
port map (
clk => clk,
valid_in => wishbone_in.ack,
insns_in => wb_rd_data,
icodes_out => cache_wr_data
);

assert LINE_SIZE mod ROW_SIZE = 0;
assert ispow2(LINE_SIZE) report "LINE_SIZE not power of 2" severity FAILURE;
assert ispow2(NUM_LINES) report "NUM_LINES not power of 2" severity FAILURE;
@ -367,13 +413,13 @@ begin
signal rd_addr : std_ulogic_vector(ROW_BITS-1 downto 0);
signal wr_addr : std_ulogic_vector(ROW_BITS-1 downto 0);
signal dout : cache_row_t;
signal wr_sel : std_ulogic_vector(ROW_SIZE-1 downto 0);
signal wr_dat : std_ulogic_vector(wishbone_in.dat'left downto 0);
signal wr_sel : std_ulogic_vector(0 downto 0);
begin
way: entity work.cache_ram
generic map (
ROW_BITS => ROW_BITS,
WIDTH => ROW_SIZE_BITS
WIDTH => ROW_WIDTH,
BYTEWID => ROW_WIDTH
)
port map (
clk => clk,
@ -382,31 +428,19 @@ begin
rd_data => dout,
wr_sel => wr_sel,
wr_addr => wr_addr,
wr_data => wr_dat
wr_data => cache_wr_data
);
process(all)
variable j: integer;
begin
-- byte-swap read data if big endian
if r.store_tag(TAG_BITS - 1) = '0' then
wr_dat <= wishbone_in.dat;
else
for ii in 0 to (wishbone_in.dat'length / 8) - 1 loop
j := ((ii / 4) * 4) + (3 - (ii mod 4));
wr_dat(ii * 8 + 7 downto ii * 8) <= wishbone_in.dat(j * 8 + 7 downto j * 8);
end loop;
end if;
do_read <= not stall_in;
do_write <= '0';
if wishbone_in.ack = '1' and replace_way = i then
if r.recv_valid = '1' and r.store_way = i then
do_write <= '1';
end if;
cache_out(i) <= dout;
rd_addr <= std_ulogic_vector(to_unsigned(req_row, ROW_BITS));
wr_addr <= std_ulogic_vector(to_unsigned(r.store_row, ROW_BITS));
for ii in 0 to ROW_SIZE-1 loop
wr_sel(ii) <= do_write;
end loop;
wr_sel(0) <= do_write;
end process;
end generate;
@ -515,6 +549,8 @@ begin
icache_comb : process(all)
variable is_hit : std_ulogic;
variable hit_way : way_t;
variable insn : std_ulogic_vector(ICWORDLEN - 1 downto 0);
variable icode : insn_code;
begin
-- Extract line, row and tag from request
if not is_X(i_in.nia) then
@ -575,11 +611,18 @@ begin
-- I prefer not to do just yet as it would force fetch2 to know about
-- some of the cache geometry information.
--
insn := (others => '0');
icode := INSN_illegal;
if r.hit_valid = '1' then
i_out.insn <= read_insn_word(r.hit_nia, cache_out(r.hit_way));
else
i_out.insn <= (others => '0');
insn := read_insn_word(r.hit_nia, cache_out(r.hit_way));
-- Currently we use only the top bit for indicating illegal
-- instructions because we know that insn_codes fit into 9 bits.
if insn(ICWORDLEN - 1) = '0' then
icode := insn_code'val(to_integer(unsigned(insn(ICWORDLEN-1 downto INSN_IMAGE_BITS))));
end if;
end if;
i_out.insn <= insn(31 downto 0);
i_out.icode <= icode;
i_out.valid <= r.hit_valid;
i_out.nia <= r.hit_nia;
i_out.stop_mark <= r.hit_smark;
@ -640,9 +683,11 @@ begin
variable snoop_addr : real_addr_t;
variable snoop_tag : cache_tag_t;
variable snoop_cache_tags : cache_tags_set_t;
variable replace_way : way_t;
begin
if rising_edge(clk) then
ev.icache_miss <= '0';
r.recv_valid <= '0';
-- On reset, clear all valid bits to force misses
if rst = '1' then
for i in index_t loop
@ -714,13 +759,13 @@ begin
" IR:" & std_ulogic'image(i_in.virt_mode) &
" SM:" & std_ulogic'image(i_in.stop_mark) &
" idx:" & integer'image(req_index) &
" way:" & integer'image(replace_way) &
" tag:" & to_hstring(req_tag) &
" RA:" & to_hstring(real_addr);
ev.icache_miss <= '1';

-- Keep track of our index and way for subsequent stores
r.store_index <= req_index;
r.recv_row <= get_row(req_raddr);
r.store_row <= get_row(req_raddr);
r.store_tag <= req_tag;
r.store_valid <= '1';
@ -740,6 +785,7 @@ begin
when CLR_TAG | WAIT_ACK =>
if r.state = CLR_TAG then
-- Get victim way from plru
replace_way := to_integer(unsigned(plru_victim(r.store_index)));
r.store_way <= replace_way;

-- Force misses on that way while reloading that line
@ -757,6 +803,19 @@ begin
r.state <= WAIT_ACK;
end if;

-- If we are writing in this cycle, mark row valid and see if we are done
if r.recv_valid = '1' then
r.rows_valid(r.store_row mod ROW_PER_LINE) <= not inval_in;
if is_last_row(r.store_row, r.end_row_ix) then
-- Cache line is now valid
cache_valids(r.store_index)(r.store_way) <= r.store_valid and not inval_in;
-- We are done
r.state <= IDLE;
end if;
-- Increment store row counter
r.store_row <= r.recv_row;
end if;

-- If we are still sending requests, was one accepted ?
if wishbone_in.stall = '0' and r.wb.stb = '1' then
-- That was the last word ? We are done sending. Clear stb.
@ -777,33 +836,27 @@ begin

-- Incoming acks processing
if wishbone_in.ack = '1' then
r.rows_valid(r.store_row mod ROW_PER_LINE) <= not inval_in;
-- Check for completion
if is_last_row(r.store_row, r.end_row_ix) then
if is_last_row(r.recv_row, r.end_row_ix) then
-- Complete wishbone cycle
r.wb.cyc <= '0';

-- Cache line is now valid
cache_valids(r.store_index)(replace_way) <= r.store_valid and not inval_in;

-- We are done
r.state <= IDLE;
end if;
r.recv_valid <= '1';

-- Increment store row counter
r.store_row <= next_row(r.store_row);
-- Increment receive row counter
r.recv_row <= next_row(r.recv_row);
end if;

when STOP_RELOAD =>
-- Wait for all outstanding requests to be satisfied, then
-- go to IDLE state.
if get_row_of_line(r.store_row) = get_row_of_line(get_row(wb_to_addr(r.wb.adr))) then
if get_row_of_line(r.recv_row) = get_row_of_line(get_row(wb_to_addr(r.wb.adr))) then
r.wb.cyc <= '0';
r.state <= IDLE;
end if;
if wishbone_in.ack = '1' then
-- Increment store row counter
r.store_row <= next_row(r.store_row);
r.recv_row <= next_row(r.recv_row);
end if;
end case;
end if;

@ -9,6 +9,7 @@ filesets:
- wishbone_types.vhdl
- common.vhdl
- fetch1.vhdl
- predecode.vhdl
- decode1.vhdl
- helpers.vhdl
- decode2.vhdl

<
@ -0,0 +1,582 @@
-- Instruction pre-decoder for microwatt
-- One cycle latency. Does 'WIDTH' instructions in parallel.

library ieee;
use ieee.std_logic_1164.all;
use ieee.numeric_std.all;

library work;
use work.common.all;
use work.decode_types.all;
use work.insn_helpers.all;

entity predecoder is
generic (
HAS_FPU : boolean := true;
WIDTH : natural := 2;
ICODE_LEN : natural := 10;
IMAGE_LEN : natural := 26
);
port (
clk : in std_ulogic;
valid_in : in std_ulogic;
insns_in : in std_ulogic_vector(WIDTH * 32 - 1 downto 0);
icodes_out : out std_ulogic_vector(WIDTH * (ICODE_LEN + IMAGE_LEN) - 1 downto 0)
);
end entity predecoder;

architecture behaviour of predecoder is

type predecoder_rom_t is array(0 to 2047) of insn_code;

constant major_predecode_rom : predecoder_rom_t := (
2#001100_00000# to 2#001100_11111# => INSN_addic,
2#001101_00000# to 2#001101_11111# => INSN_addic_dot,
2#001110_00000# to 2#001110_11111# => INSN_addi,
2#001111_00000# to 2#001111_11111# => INSN_addis,
2#010011_00100# to 2#010011_00101# => INSN_addpcis,
2#011100_00000# to 2#011100_11111# => INSN_andi_dot,
2#011101_00000# to 2#011101_11111# => INSN_andis_dot,
2#000000_00000# => INSN_attn,
2#010010_00000# to 2#010010_11111# => INSN_b,
2#010000_00000# to 2#010000_11111# => INSN_bc,
2#001011_00000# to 2#001011_11111# => INSN_cmpi,
2#001010_00000# to 2#001010_11111# => INSN_cmpli,
2#100010_00000# to 2#100010_11111# => INSN_lbz,
2#100011_00000# to 2#100011_11111# => INSN_lbzu,
2#110010_00000# to 2#110010_11111# => INSN_lfd,
2#110011_00000# to 2#110011_11111# => INSN_lfdu,
2#110000_00000# to 2#110000_11111# => INSN_lfs,
2#110001_00000# to 2#110001_11111# => INSN_lfsu,
2#101010_00000# to 2#101010_11111# => INSN_lha,
2#101011_00000# to 2#101011_11111# => INSN_lhau,
2#101000_00000# to 2#101000_11111# => INSN_lhz,
2#101001_00000# to 2#101001_11111# => INSN_lhzu,
2#100000_00000# to 2#100000_11111# => INSN_lwz,
2#100001_00000# to 2#100001_11111# => INSN_lwzu,
2#000111_00000# to 2#000111_11111# => INSN_mulli,
2#011000_00000# to 2#011000_11111# => INSN_ori,
2#011001_00000# to 2#011001_11111# => INSN_oris,
2#010100_00000# to 2#010100_11111# => INSN_rlwimi,
2#010101_00000# to 2#010101_11111# => INSN_rlwinm,
2#010111_00000# to 2#010111_11111# => INSN_rlwnm,
2#010001_00000# to 2#010001_11111# => INSN_sc,
2#100110_00000# to 2#100110_11111# => INSN_stb,
2#100111_00000# to 2#100111_11111# => INSN_stbu,
2#110110_00000# to 2#110110_11111# => INSN_stfd,
2#110111_00000# to 2#110111_11111# => INSN_stfdu,
2#110100_00000# to 2#110100_11111# => INSN_stfs,
2#110101_00000# to 2#110101_11111# => INSN_stfsu,
2#101100_00000# to 2#101100_11111# => INSN_sth,
2#101101_00000# to 2#101101_11111# => INSN_sthu,
2#100100_00000# to 2#100100_11111# => INSN_stw,
2#100101_00000# to 2#100101_11111# => INSN_stwu,
2#001000_00000# to 2#001000_11111# => INSN_subfic,
2#000010_00000# to 2#000010_11111# => INSN_tdi,
2#000011_00000# to 2#000011_11111# => INSN_twi,
2#011010_00000# to 2#011010_11111# => INSN_xori,
2#011011_00000# to 2#011011_11111# => INSN_xoris,
-- major opcode 4
2#000100_10000# => INSN_maddhd,
2#000100_10001# => INSN_maddhdu,
2#000100_10011# => INSN_maddld,
-- major opcode 30
2#011110_01000# to 2#011110_01001# => INSN_rldic,
2#011110_01010# to 2#011110_01011# => INSN_rldic,
2#011110_00000# to 2#011110_00001# => INSN_rldicl,
2#011110_00010# to 2#011110_00011# => INSN_rldicl,
2#011110_00100# to 2#011110_00101# => INSN_rldicr,
2#011110_00110# to 2#011110_00111# => INSN_rldicr,
2#011110_01100# to 2#011110_01101# => INSN_rldimi,
2#011110_01110# to 2#011110_01111# => INSN_rldimi,
2#011110_10000# to 2#011110_10001# => INSN_rldcl,
2#011110_10010# to 2#011110_10011# => INSN_rldcr,
-- major opcode 58
2#111010_00000# => INSN_ld,
2#111010_00001# => INSN_ldu,
2#111010_00010# => INSN_lwa,
2#111010_00100# => INSN_ld,
2#111010_00101# => INSN_ldu,
2#111010_00110# => INSN_lwa,
2#111010_01000# => INSN_ld,
2#111010_01001# => INSN_ldu,
2#111010_01010# => INSN_lwa,
2#111010_01100# => INSN_ld,
2#111010_01101# => INSN_ldu,
2#111010_01110# => INSN_lwa,
2#111010_10000# => INSN_ld,
2#111010_10001# => INSN_ldu,
2#111010_10010# => INSN_lwa,
2#111010_10100# => INSN_ld,
2#111010_10101# => INSN_ldu,
2#111010_10110# => INSN_lwa,
2#111010_11000# => INSN_ld,
2#111010_11001# => INSN_ldu,
2#111010_11010# => INSN_lwa,
2#111010_11100# => INSN_ld,
2#111010_11101# => INSN_ldu,
2#111010_11110# => INSN_lwa,
-- major opcode 59
2#111011_00100# to 2#111011_00101# => INSN_fdivs,
2#111011_01000# to 2#111011_01001# => INSN_fsubs,
2#111011_01010# to 2#111011_01011# => INSN_fadds,
2#111011_01100# to 2#111011_01101# => INSN_fsqrts,
2#111011_10000# to 2#111011_10001# => INSN_fres,
2#111011_10010# to 2#111011_10011# => INSN_fmuls,
2#111011_10100# to 2#111011_10101# => INSN_frsqrtes,
2#111011_11000# to 2#111011_11001# => INSN_fmsubs,
2#111011_11010# to 2#111011_11011# => INSN_fmadds,
2#111011_11100# to 2#111011_11101# => INSN_fnmsubs,
2#111011_11110# to 2#111011_11111# => INSN_fnmadds,
-- major opcode 62
2#111110_00000# => INSN_std,
2#111110_00001# => INSN_stdu,
2#111110_00100# => INSN_std,
2#111110_00101# => INSN_stdu,
2#111110_01000# => INSN_std,
2#111110_01001# => INSN_stdu,
2#111110_01100# => INSN_std,
2#111110_01101# => INSN_stdu,
2#111110_10000# => INSN_std,
2#111110_10001# => INSN_stdu,
2#111110_10100# => INSN_std,
2#111110_10101# => INSN_stdu,
2#111110_11000# => INSN_std,
2#111110_11001# => INSN_stdu,
2#111110_11100# => INSN_std,
2#111110_11101# => INSN_stdu,
-- major opcode 63
2#111111_00100# to 2#111111_00101# => INSN_fdiv,
2#111111_01000# to 2#111111_01001# => INSN_fsub,
2#111111_01010# to 2#111111_01011# => INSN_fadd,
2#111111_01100# to 2#111111_01101# => INSN_fsqrt,
2#111111_01110# to 2#111111_01111# => INSN_fsel,
2#111111_10000# to 2#111111_10001# => INSN_fre,
2#111111_10010# to 2#111111_10011# => INSN_fmul,
2#111111_10100# to 2#111111_10101# => INSN_frsqrte,
2#111111_11000# to 2#111111_11001# => INSN_fmsub,
2#111111_11010# to 2#111111_11011# => INSN_fmadd,
2#111111_11100# to 2#111111_11101# => INSN_fnmsub,
2#111111_11110# to 2#111111_11111# => INSN_fnmadd,
others => INSN_illegal
);

constant row_predecode_rom : predecoder_rom_t := (
-- Major opcode 31
-- Address bits are 0, insn(10:1)
2#0_01000_01010# => INSN_add,
2#0_11000_01010# => INSN_add, -- addo
2#0_00000_01010# => INSN_addc,
2#0_10000_01010# => INSN_addc, -- addco
2#0_00100_01010# => INSN_adde,
2#0_10100_01010# => INSN_adde, -- addeo
2#0_00101_01010# => INSN_addex,
2#0_00010_01010# => INSN_addg6s,
2#0_00111_01010# => INSN_addme,
2#0_10111_01010# => INSN_addme, -- addmeo
2#0_00110_01010# => INSN_addze,
2#0_10110_01010# => INSN_addze, -- addzeo
2#0_00000_11100# => INSN_and,
2#0_00001_11100# => INSN_andc,
2#0_00111_11100# => INSN_bperm,
2#0_01001_11010# => INSN_cbcdtd,
2#0_01000_11010# => INSN_cdtbcd,
2#0_00000_00000# => INSN_cmp,
2#0_01111_11100# => INSN_cmpb,
2#0_00111_00000# => INSN_cmpeqb,
2#0_00001_00000# => INSN_cmpl,
2#0_00110_00000# => INSN_cmprb,
2#0_00001_11010# => INSN_cntlzd,
2#0_00000_11010# => INSN_cntlzw,
2#0_10001_11010# => INSN_cnttzd,
2#0_10000_11010# => INSN_cnttzw,
2#0_10111_10011# => INSN_darn,
2#0_00010_10110# => INSN_dcbf,
2#0_00001_10110# => INSN_dcbst,
2#0_01000_10110# => INSN_dcbt,
2#0_00111_10110# => INSN_dcbtst,
2#0_11111_10110# => INSN_dcbz,
2#0_01100_01001# => INSN_divdeu,
2#0_11100_01001# => INSN_divdeu, -- divdeuo
2#0_01100_01011# => INSN_divweu,
2#0_11100_01011# => INSN_divweu, -- divweuo
2#0_01101_01001# => INSN_divde,
2#0_11101_01001# => INSN_divde, -- divdeo
2#0_01101_01011# => INSN_divwe,
2#0_11101_01011# => INSN_divwe, -- divweo
2#0_01110_01001# => INSN_divdu,
2#0_11110_01001# => INSN_divdu, -- divduo
2#0_01110_01011# => INSN_divwu,
2#0_11110_01011# => INSN_divwu, -- divwuo
2#0_01111_01001# => INSN_divd,
2#0_11111_01001# => INSN_divd, -- divdo
2#0_01111_01011# => INSN_divw,
2#0_11111_01011# => INSN_divw, -- divwo
2#0_11001_10110# => INSN_nop, -- dss
2#0_01010_10110# => INSN_nop, -- dst
2#0_01011_10110# => INSN_nop, -- dstst
2#0_11010_10110# => INSN_eieio,
2#0_01000_11100# => INSN_eqv,
2#0_11101_11010# => INSN_extsb,
2#0_11100_11010# => INSN_extsh,
2#0_11110_11010# => INSN_extsw,
2#0_11011_11010# => INSN_extswsli,
2#0_11011_11011# => INSN_extswsli,
2#0_11110_10110# => INSN_icbi,
2#0_00000_10110# => INSN_icbt,
2#0_00000_01111# => INSN_isel,
2#0_00001_01111# => INSN_isel,
2#0_00010_01111# => INSN_isel,
2#0_00011_01111# => INSN_isel,
2#0_00100_01111# => INSN_isel,
2#0_00101_01111# => INSN_isel,
2#0_00110_01111# => INSN_isel,
2#0_00111_01111# => INSN_isel,
2#0_01000_01111# => INSN_isel,
2#0_01001_01111# => INSN_isel,
2#0_01010_01111# => INSN_isel,
2#0_01011_01111# => INSN_isel,
2#0_01100_01111# => INSN_isel,
2#0_01101_01111# => INSN_isel,
2#0_01110_01111# => INSN_isel,
2#0_01111_01111# => INSN_isel,
2#0_10000_01111# => INSN_isel,
2#0_10001_01111# => INSN_isel,
2#0_10010_01111# => INSN_isel,
2#0_10011_01111# => INSN_isel,
2#0_10100_01111# => INSN_isel,
2#0_10101_01111# => INSN_isel,
2#0_10110_01111# => INSN_isel,
2#0_10111_01111# => INSN_isel,
2#0_11000_01111# => INSN_isel,
2#0_11001_01111# => INSN_isel,
2#0_11010_01111# => INSN_isel,
2#0_11011_01111# => INSN_isel,
2#0_11100_01111# => INSN_isel,
2#0_11101_01111# => INSN_isel,
2#0_11110_01111# => INSN_isel,
2#0_11111_01111# => INSN_isel,
2#0_00001_10100# => INSN_lbarx,
2#0_11010_10101# => INSN_lbzcix,
2#0_00011_10111# => INSN_lbzux,
2#0_00010_10111# => INSN_lbzx,
2#0_00010_10100# => INSN_ldarx,
2#0_10000_10100# => INSN_ldbrx,
2#0_11011_10101# => INSN_ldcix,
2#0_00001_10101# => INSN_ldux,
2#0_00000_10101# => INSN_ldx,
2#0_10010_10111# => INSN_lfdx,
2#0_10011_10111# => INSN_lfdux,
2#0_11010_10111# => INSN_lfiwax,
2#0_11011_10111# => INSN_lfiwzx,
2#0_10000_10111# => INSN_lfsx,
2#0_10001_10111# => INSN_lfsux,
2#0_00011_10100# => INSN_lharx,
2#0_01011_10111# => INSN_lhaux,
2#0_01010_10111# => INSN_lhax,
2#0_11000_10110# => INSN_lhbrx,
2#0_11001_10101# => INSN_lhzcix,
2#0_01001_10111# => INSN_lhzux,
2#0_01000_10111# => INSN_lhzx,
2#0_00000_10100# => INSN_lwarx,
2#0_01011_10101# => INSN_lwaux,
2#0_01010_10101# => INSN_lwax,
2#0_10000_10110# => INSN_lwbrx,
2#0_11000_10101# => INSN_lwzcix,
2#0_00001_10111# => INSN_lwzux,
2#0_00000_10111# => INSN_lwzx,
2#0_10010_00000# => INSN_mcrxrx,
2#0_00000_10011# => INSN_mfcr,
2#0_00010_10011# => INSN_mfmsr,
2#0_01010_10011# => INSN_mfspr,
2#0_01000_01001# => INSN_modud,
2#0_01000_01011# => INSN_moduw,
2#0_11000_01001# => INSN_modsd,
2#0_11000_01011# => INSN_modsw,
2#0_00100_10000# => INSN_mtcrf,
2#0_00100_10010# => INSN_mtmsr,
2#0_00101_10010# => INSN_mtmsrd,
2#0_01110_10011# => INSN_mtspr,
2#0_00010_01001# => INSN_mulhd,
2#0_00000_01001# => INSN_mulhdu,
2#0_00010_01011# => INSN_mulhw,
2#0_00000_01011# => INSN_mulhwu,
-- next 4 have reserved bit set
2#0_10010_01001# => INSN_mulhd,
2#0_10000_01001# => INSN_mulhdu,
2#0_10010_01011# => INSN_mulhw,
2#0_10000_01011# => INSN_mulhwu,
2#0_00111_01001# => INSN_mulld,
2#0_10111_01001# => INSN_mulld, -- mulldo
2#0_00111_01011# => INSN_mullw,
2#0_10111_01011# => INSN_mullw, -- mullwo
2#0_01110_11100# => INSN_nand,
2#0_00011_01000# => INSN_neg,
2#0_10011_01000# => INSN_neg, -- nego
-- next 8 are reserved no-op instructions
2#0_10000_10010# => INSN_nop,
2#0_10001_10010# => INSN_nop,
2#0_10010_10010# => INSN_nop,
2#0_10011_10010# => INSN_nop,
2#0_10100_10010# => INSN_nop,
2#0_10101_10010# => INSN_nop,
2#0_10110_10010# => INSN_nop,
2#0_10111_10010# => INSN_nop,
2#0_00011_11100# => INSN_nor,
2#0_01101_11100# => INSN_or,
2#0_01100_11100# => INSN_orc,
2#0_00011_11010# => INSN_popcntb,
2#0_01111_11010# => INSN_popcntd,
2#0_01011_11010# => INSN_popcntw,
2#0_00101_11010# => INSN_prtyd,
2#0_00100_11010# => INSN_prtyw,
2#0_00100_00000# => INSN_setb,
2#0_01111_10010# => INSN_slbia,
2#0_00000_11011# => INSN_sld,
2#0_00000_11000# => INSN_slw,
2#0_11000_11010# => INSN_srad,
2#0_11001_11010# => INSN_sradi,
2#0_11001_11011# => INSN_sradi,
2#0_11000_11000# => INSN_sraw,
2#0_11001_11000# => INSN_srawi,
2#0_10000_11011# => INSN_srd,
2#0_10000_11000# => INSN_srw,
2#0_11110_10101# => INSN_stbcix,
2#0_10101_10110# => INSN_stbcx,
2#0_00111_10111# => INSN_stbux,
2#0_00110_10111# => INSN_stbx,
2#0_10100_10100# => INSN_stdbrx,
2#0_11111_10101# => INSN_stdcix,
2#0_00110_10110# => INSN_stdcx,
2#0_00101_10101# => INSN_stdux,
2#0_00100_10101# => INSN_stdx,
2#0_10110_10111# => INSN_stfdx,
2#0_10111_10111# => INSN_stfdux,
2#0_11110_10111# => INSN_stfiwx,
2#0_10100_10111# => INSN_stfsx,
2#0_10101_10111# => INSN_stfsux,
2#0_11100_10110# => INSN_sthbrx,
2#0_11101_10101# => INSN_sthcix,
2#0_10110_10110# => INSN_sthcx,
2#0_01101_10111# => INSN_sthux,
2#0_01100_10111# => INSN_sthx,
2#0_10100_10110# => INSN_stwbrx,
2#0_11100_10101# => INSN_stwcix,
2#0_00100_10110# => INSN_stwcx,
2#0_00101_10111# => INSN_stwux,
2#0_00100_10111# => INSN_stwx,
2#0_00001_01000# => INSN_subf,
2#0_10001_01000# => INSN_subf, -- subfo
2#0_00000_01000# => INSN_subfc,
2#0_10000_01000# => INSN_subfc, -- subfco
2#0_00100_01000# => INSN_subfe,
2#0_10100_01000# => INSN_subfe, -- subfeo
2#0_00111_01000# => INSN_subfme,
2#0_10111_01000# => INSN_subfme, -- subfmeo
2#0_00110_01000# => INSN_subfze,
2#0_10110_01000# => INSN_subfze, -- subfzeo
2#0_10010_10110# => INSN_sync,
2#0_00010_00100# => INSN_td,
2#0_00000_00100# => INSN_tw,
2#0_01001_10010# => INSN_tlbie,
2#0_01000_10010# => INSN_tlbiel,
2#0_10001_10110# => INSN_tlbsync,
2#0_00000_11110# => INSN_wait,
2#0_01001_11100# => INSN_xor,

-- Major opcode 19
-- Columns with insn(4) = '1' are all illegal and not mapped here; to
-- fit into 2048 entries, the columns are remapped so that 16-24 are
-- stored here as 8-15; in other words the address bits are
-- 1, insn(10..6), 1, insn(5), insn(3..1)
2#1_10000_11000# => INSN_bcctr,
2#1_00000_11000# => INSN_bclr,
2#1_10001_11000# => INSN_bctar,
2#1_01000_10001# => INSN_crand,
2#1_00100_10001# => INSN_crandc,
2#1_01001_10001# => INSN_creqv,
2#1_00111_10001# => INSN_crnand,
2#1_00001_10001# => INSN_crnor,
2#1_01110_10001# => INSN_cror,
2#1_01101_10001# => INSN_crorc,
2#1_00110_10001# => INSN_crxor,
2#1_00100_11110# => INSN_isync,
2#1_00000_10000# => INSN_mcrf,
2#1_00000_11010# => INSN_rfid,

-- Major opcode 59
-- Only column 14 is valid here; columns 16-31 are handled in the major table
-- Column 14 is mapped to column 6 of the space which is
-- mostly used for opcode 19.
2#1_11010_10110# => INSN_fcfids,
2#1_11110_10110# => INSN_fcfidus,

-- Major opcode 63
-- Columns 0-15 are mapped here; columns 16-31 are in the major table.
-- Address bits are 1, insn(10:6), 0, insn(4:1)
2#1_00000_00000# => INSN_fcmpu,
2#1_00001_00000# => INSN_fcmpo,
2#1_00010_00000# => INSN_mcrfs,
2#1_00100_00000# => INSN_ftdiv,
2#1_00101_00000# => INSN_ftsqrt,
2#1_00001_00110# => INSN_mtfsb,
2#1_00010_00110# => INSN_mtfsb,
2#1_00100_00110# => INSN_mtfsfi,
2#1_11010_00110# => INSN_fmrgow,
2#1_11110_00110# => INSN_fmrgew,
2#1_10010_00111# => INSN_mffs,
2#1_10110_00111# => INSN_mtfsf,
2#1_00000_01000# => INSN_fcpsgn,
2#1_00001_01000# => INSN_fneg,
2#1_00010_01000# => INSN_fmr,
2#1_00100_01000# => INSN_fnabs,
2#1_01000_01000# => INSN_fabs,
2#1_01100_01000# => INSN_frin,
2#1_01101_01000# => INSN_friz,
2#1_01110_01000# => INSN_frip,
2#1_01111_01000# => INSN_frim,
2#1_00000_01100# => INSN_frsp,
2#1_00000_01110# => INSN_fctiw,
2#1_00100_01110# => INSN_fctiwu,
2#1_11001_01110# => INSN_fctid,
2#1_11010_01110# => INSN_fcfid,
2#1_11101_01110# => INSN_fctidu,
2#1_11110_01110# => INSN_fcfidu,
2#1_00000_01111# => INSN_fctiwz,
2#1_00100_01111# => INSN_fctiwuz,
2#1_11001_01111# => INSN_fctidz,
2#1_11101_01111# => INSN_fctiduz,

others => INSN_illegal
);

constant IOUT_LEN : natural := ICODE_LEN + IMAGE_LEN;

type predec_t is record
image : std_ulogic_vector(31 downto 0);
maj_predecode : insn_code;
row_predecode : insn_code;
end record;

subtype index_t is integer range 0 to WIDTH-1;
type predec_array is array(index_t) of predec_t;

signal pred : predec_array;

begin
predecode_0: process(clk)
variable majaddr : std_ulogic_vector(10 downto 0);
variable rowaddr : std_ulogic_vector(10 downto 0);
variable iword : std_ulogic_vector(31 downto 0);
begin
if rising_edge(clk) then
for i in index_t loop
if valid_in = '1' then
iword := insns_in(i * 32 + 31 downto i * 32);

majaddr := iword(31 downto 26) & iword(4 downto 0);

-- row_predecode_rom is used for op 19, 31, 59, 63
-- addr bit 10 is 0 for op 31, 1 for 19, 59, 63
rowaddr(10) := iword(31) or not iword(29);
rowaddr(9 downto 5) := iword(10 downto 6);
if iword(28) = '0' then
-- op 19 and op 59
rowaddr(4 downto 3) := '1' & iword(5);
else
-- op 31 and 63; for 63 we only use this when iword(5) = '0'
rowaddr(4 downto 3) := iword(5 downto 4);
end if;
rowaddr(2 downto 0) := iword(3 downto 1);

pred(i).image <= iword;
pred(i).maj_predecode <= major_predecode_rom(to_integer(unsigned(majaddr)));
pred(i).row_predecode <= row_predecode_rom(to_integer(unsigned(rowaddr)));
else
pred(i).image <= (others => '0');
pred(i).maj_predecode <= INSN_illegal;
pred(i).row_predecode <= INSN_illegal;
end if;
end loop;
end if;
end process;

predecode_1: process(all)
variable iword : std_ulogic_vector(31 downto 0);
variable use_row : std_ulogic;
variable illegal : std_ulogic;
variable ici : std_ulogic_vector(IOUT_LEN - 1 downto 0);
variable icode : insn_code;
begin
for i in index_t loop
iword := pred(i).image;
icode := pred(i).maj_predecode;
use_row := '0';
illegal := '0';

case iword(31 downto 26) is
when "000100" => -- 4
-- major opcode 4, mostly VMX/VSX stuff but also some integer ops (madd*)
illegal := not iword(5);

when "010011" => -- 19
-- Columns 8-15 and 24-31 don't have any valid instructions
-- (where insn(5..1) is the column number).
-- addpcis (column 2) is in the major table
-- Other valid columns are mapped to columns in the second
-- half of the row table: columns 0-1 are mapped to 16-17
-- and 16-23 are mapped to 24-31.
illegal := iword(4);
use_row := iword(5) or (not iword(3) and not iword(2));

when "011000" => -- 24
-- ori, special-case the standard NOP
if std_match(iword, "01100000000000000000000000000000") then
icode := INSN_nop;
end if;

when "011111" => -- 31
-- major opcode 31, lots of things
-- Use the first half of the row table for all columns
use_row := '1';

when "111011" => -- 59
-- floating point operations, mostly single-precision
-- Columns 0-11 are illegal; columns 12-15 are mapped
-- to columns 20-23 in the second half of the row table,
-- and columns 16-31 are in the major table.
illegal := not iword(5) and (not iword(4) or not iword(3));
use_row := not iword(5);

when "111111" => -- 63
-- floating point operations, general and double-precision
-- Use columns 0-15 of the second half of the row table
-- for columns 0-15, and the major table for columns 16-31.
use_row := not iword(5);

when others =>
end case;
if use_row = '1' then
icode := pred(i).row_predecode;
end if;