


library ieee;




use ieee.std_logic_1164.all;




use ieee.numeric_std.all;








library work;




use work.common.all;




use work.decode_types.all;








entity divider is




port (




clk : in std_logic;




rst : in std_logic;




d_in : in Execute1ToDividerType;




d_out : out DividerToExecute1Type




);




end entity divider;








architecture behaviour of divider is

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



signal dend : std_ulogic_vector(128 downto 0);




signal div : unsigned(63 downto 0);




signal quot : std_ulogic_vector(63 downto 0);




signal result : std_ulogic_vector(63 downto 0);




signal sresult : std_ulogic_vector(64 downto 0);




signal oresult : std_ulogic_vector(63 downto 0);




signal running : std_ulogic;




signal count : unsigned(6 downto 0);




signal neg_result : std_ulogic;




signal is_modulus : std_ulogic;




signal is_32bit : std_ulogic;




signal extended : std_ulogic;

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



signal is_signed : std_ulogic;




signal overflow : std_ulogic;




signal ovf32 : std_ulogic;

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



signal did_ovf : std_ulogic;




begin




divider_0: process(clk)




begin




if rising_edge(clk) then

Add a second execute stage to the pipeline
This adds a second execute stage to the pipeline, in order to match up
the length of the pipeline through loadstore and dcache with the
length through execute1. This will ultimately enable us to get rid of
the 1cycle bubble that we currently have when issuing ALU
instructions after one or more LSU instructions.
Most ALU instructions execute in the first stage, except for
countzeroes and popcount instructions (which take two cycles and do
some of their work in the second stage) and mfspr/mtspr to "slow" SPRs
(TB, DEC, PVR, LOGA/LOGD, CFAR). Multiply and divide/mod instructions
take several cycles but the instruction stays in the first stage (ex1)
and ex1.busy is asserted until the operation is complete.
There is currently a bypass from the first stage but not the second
stage. Performance is down somewhat because of that and because this
doesn't yet eliminate the bubble between LSU and ALU instructions.
The forwarding of XER common bits has been changed somewhat because
now there is another pipeline stage between ex1 and the committed
state in cr_file. The simplest thing for now is to record the last
value written and use that, unless there has been a flush, in which
case the committed state (obtained via e_in.xerc) is used.
Note that this fixes what was previously a benign bug in control.vhdl,
where it was possible for control to forget an instructions dependency
on a value from a previous instruction (a GPR or the CR) if this
instruction writes the value and the instruction gets to the point
where it could issue but is blocked by the busy signal from execute1.
In that situation, control may incorrectly not indicate that a bypass
should be used. That didn't matter previously because, for ALU and
FPU instructions, there was only one previous instruction in flight
and once the current instruction could issue, the previous instruction
was completing and the correct value would be obtained from
register_file or cr_file. For loadstore instructions there could be
two being executed, but because there are no bypass paths, failing to
indicate use of a bypass path is fine.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
2 years ago



if rst = '1' or d_in.flush = '1' then




dend <= (others => '0');




div <= (others => '0');




quot <= (others => '0');




running <= '0';




count <= "0000000";




is_32bit <= '0';




overflow <= '0';




elsif d_in.valid = '1' then




if d_in.is_extended = '1' then

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



dend <= '0' & d_in.dividend & x"0000000000000000";




else

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



dend <= '0' & x"0000000000000000" & d_in.dividend;




end if;




div <= unsigned(d_in.divisor);




quot <= (others => '0');




neg_result <= d_in.neg_result;




is_modulus <= d_in.is_modulus;




extended <= d_in.is_extended;




is_32bit <= d_in.is_32bit;

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



is_signed <= d_in.is_signed;




count <= "1111111";




running <= '1';

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



overflow <= '0';




ovf32 <= '0';




elsif running = '1' then




if count = "0111111" then




running <= '0';




end if;

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



overflow <= quot(63);




if dend(128) = '1' or unsigned(dend(127 downto 64)) >= div then




ovf32 <= ovf32 or quot(31);

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



dend <= std_ulogic_vector(unsigned(dend(127 downto 64))  div) &




dend(63 downto 0) & '0';




quot <= quot(62 downto 0) & '1';




count <= count + 1;

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



elsif dend(128 downto 57) = x"000000000000000000" and count(6 downto 3) /= "0111" then




 consume 8 bits of zeroes in one cycle




ovf32 <= or (ovf32 & quot(31 downto 24));

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



dend <= dend(120 downto 0) & x"00";




quot <= quot(55 downto 0) & x"00";




count <= count + 8;




else




ovf32 <= ovf32 or quot(31);

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



dend <= dend(127 downto 0) & '0';




quot <= quot(62 downto 0) & '0';




count <= count + 1;




end if;




else




count <= "0000000";




end if;




end if;




end process;








divider_1: process(all)




begin




if is_modulus = '1' then

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



result <= dend(128 downto 65);




else




result <= quot;




end if;




if neg_result = '1' then




sresult <= std_ulogic_vector( signed('0' & result));




else




sresult <= '0' & result;




end if;

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



did_ovf <= '0';




if is_32bit = '0' then




did_ovf <= overflow or (is_signed and (sresult(64) xor sresult(63)));

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



elsif is_signed = '1' then




if ovf32 = '1' or sresult(32) /= sresult(31) then

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



did_ovf <= '1';




end if;




else




did_ovf <= ovf32;

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



end if;




if did_ovf = '1' then




oresult <= (others => '0');

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



elsif (is_32bit = '1') and (is_modulus = '0') then




 32bit divisions set the top 32 bits of the result to 0




oresult <= x"00000000" & sresult(31 downto 0);

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



else




oresult <= sresult(63 downto 0);

divider: Return 0 for invalid and overflow cases, like P9 does
This adds logic to detect the cases where the quotient of the
division overflows the range of the output representation, and
return all zeroes in those cases, which is what POWER9 does.
To do this, we extend the dividend register by 1 bit and we do
an extra step in the division process to get a 2^64 bit of the
quotient, which ends up in the 'overflow' signal. This catches all
the cases where dividend >= 2^64 * divisor, including the case
where divisor = 0, and the divde/divdeu cases where RA >= RB.
Then, in the output stage, we also check that the result fits in
the representable range, which depends on whether the division is
a signed division or not, and whether it is a 32bit or 64bit
division. If dividend >= 2^64 or the result doesn't fit in the
representable range, write_data is set to 0 and write_cr_data to
0x20000000 (i.e. cr0.eq = 1).
POWER9 sets the top 32 bits of the result to zero for 32bit signed
divisions, and sets CR0 when RC=1 according to the 64bit value
(i.e. CR0.LT is always 0 for 32bit signed divisions, even if the
32bit result is negative). However, modsw with a negative result
sets the top 32 bits to all 1s. We follow suit.
This updates divider_tb to check the invalid cases as well as the
valid case.
This also fixes a small bug where the reset signal for the divider
was driven from rst when it should have been driven from core_rst.
Signedoffby: Paul Mackerras <paulus@ozlabs.org>
5 years ago



end if;




end process;








divider_out: process(clk)




begin




if rising_edge(clk) then




d_out.valid <= '0';




d_out.write_reg_data <= oresult;




d_out.overflow <= did_ovf;




if count = "1000000" then




d_out.valid <= '1';




end if;




end if;




end process;








end architecture behaviour;
