This implements the floating square-root calculation using a table
lookup of the inverse square root approximation, followed by three
iterations of Goldschmidt's algorithm, which gives estimates of both
sqrt(FRB) and 1/sqrt(FRB). Then the residual is calculated as
FRB - R * R and that is multiplied by the 1/sqrt(FRB) estimate to get
an adjustment to R. The residual and the adjustment can be negative,
and since we have an unsigned multiplier, the upper bits can be wrong.
In practice the adjustment fits into an 8-bit signed value, and the
bottom 8 bits of the adjustment product are correct, so we sign-extend
them, divide by 4 (because R is in 10.54 format) and add them to R.
Finally the residual is calculated again and compared to 2*R+1 to see
if a final increment is needed. Then the result is rounded and
written back.
This implements fsqrts as fsqrt, but with rounding to single precision
and underflow/overflow calculation using the single-precision exponent
range. This could be optimized later.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This implements frsqrte by table lookup. We first normalize the input
if necessary and adjust so that the exponent is even, giving us a
mantissa value in the range [1.0, 4.0), which is then used to look up
an entry in a 768-entry table. The 768 entries are appended to the
table for reciprocal estimates, giving a table of 1024 entries in
total. frsqrtes is implemented identically to frsqrte.
The estimate supplied is accurate to 1 part in 1024 or better.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This just returns the value from the inverse lookup table. The result
is accurate to better than one part in 512 (the architecture requires
1/256).
This also adds a simple test, which relies on the particular values in
the inverse lookup table, so it is not a general test.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This implements floating-point division A/B by a process that starts
with normalizing both inputs if necessary. Then an estimate of 1/B
from a lookup table is refined by 3 Newton-Raphson iterations and then
multiplied by A to get a quotient. The remainder is calculated as
A - R * B (where R is the result, i.e. the quotient) and the remainder
is compared to 0 and to B to see whether the quotient needs to be
incremented by 1. The calculations of 1 / B are done with 56 fraction
bits and intermediate results are truncated rather than rounded,
meaning that the final estimate of 1 / B is always correct or a little
bit low, never too high, and thus the calculated quotient is correct
or 1 unit too low. Doing the estimate of 1 / B with sufficient
precision that the quotient is always correct to the last bit without
needing any adjustment would require many more bits of precision.
This implements fdivs by computing a double-precision quotient and
then rounding it to single precision. It would be possible to
optimize this by e.g. doing only 2 iterations of Newton-Raphson and
then doing the remainder calculation and adjustment at single
precision rather than double precision.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This implements the fmul and fmuls instructions.
For fmul[s] with denormalized operands we normalize the inputs
before doing the multiplication, to eliminate the need for doing
count-leading-zeroes on P. This adds 3 or 5 cycles to the
execution time when one or both operands are denormalized.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This implements fctiw, fctiwz, fctiwu, fctiwuz, fctid, fctidz, fctidu
and fctiduz, and adds tests for them.
There are some subtleties around the setting of the inexact (XX) and
invalid conversion (VXCVI) flags in the FPSCR. If the rounded value
ends up being out of range, we need to set VXCVI and not XX. For a
conversion to unsigned word or doubleword of a negative value that
rounds to zero, we need to set XX and not VXCVI.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This brings in the invalid exception for the case of frsp with a
signalling NaN as input, and the need to be able to convert a
signalling NaN to a quiet NaN.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This implements fcfid, fcfidu, fcfids and fcfidus, which convert
64-bit integer values in an FPR into a floating-point value.
This brings in a lot of the datapath that will be needed in
future, including the shifter, adder, mask generator and
count-leading-zeroes logic, along with the machinery for rounding
to single-precision or double-precision, detecting inexact results,
signalling inexact-result exceptions, and updating result flags
in the FPSCR.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This implements fmr, fneg, fabs, fnabs and fcpsgn and adds tests
for them.
This adds logic to unpack and repack floating-point data from the
64-bit packed form (as stored in memory and the register file) into
the unpacked form in the fpr_reg_type record. This is not strictly
necessary for fmr et al., but will be useful for when we do actual
arithmetic.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This tests mffs, mtfsf and the generation of floating-point type
program interrupts that occur as a result of mtfsf.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This adds the skeleton of a floating-point unit and implements the
mffs and mtfsf instructions.
Execute1 sends FP instructions to the FPU and receives busy,
exception, FP interrupt and illegal interrupt signals from it.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This adds code to loadstore1 to convert between single-precision and
double-precision formats, and implements the lfs* and stfs*
instructions. The conversion processes are described in Power ISA
v3.1 Book 1 sections 4.6.2 and 4.6.3.
These conversions take one cycle, so lfs* and stfs* are one cycle
slower than lfd* and stfd*.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This tests that floating-point unavailable exceptions occur as expected
on FP loads and stores, and that the simple FP loads and stores appear
to give reasonable results.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This extends the register file so it can hold FPR values, and
implements the FP loads and stores that do not require conversion
between single and double precision.
We now have the FP, FE0 and FE1 bits in MSR. FP loads and stores
cause a FP unavailable interrupt if MSR[FP] = 0.
The FPU facilities are optional and their presence is controlled by
the HAS_FPU generic passed down from the top-level board file. It
defaults to true for all except the A7-35 boards.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Trace interrupts occur when the MSR[TE] field is non-zero and an
instruction other than rfid has been successfully completed. A trace
interrupt occurs before the next instruction is executed or any
asynchronous interrupt is taken.
Since the trace interrupt is defined to set SRR1 bits depending on
whether the traced instruction is a load or an instruction treated as
a load, or a store or an instruction treated as a store, we need to
make sure the treated-as-a-load instructions (icbi, icbt, dcbt, dcbst,
dcbf) and the treated-as-a-store instructions (dcbtst, dcbz) have the
correct opcodes in decode1. Several of them were previously marked as
OP_NOP.
We don't yet implement the SIAR or SDAR registers, which should be set
by trace interrupts.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
In the cases where we need to override the values from the decode ROMs,
we now do that overriding after the clock edge (eating into decode2's
cycle) rather than before. This helps timing a little.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This checks that the instructions seem to update memory as expected,
and also that they generate alignment interrupts when necessary.
We don't check whether the memory update is atomic as we don't have
SMP yet.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Load-and-reserve and store-conditional instructions are required to
generate an alignment interrupt (0x600 vector) if their EA is not
aligned. Implement this.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
In 32-bit mode, effective addresses are truncated to 32 bits, both for
instruction fetches and data accesses, and CR0 is set for Rc=1 (record
form) instructions based on the lower 32 bits of the result rather
than all 64 bits.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Big-endian mode affects both instruction fetches and data accesses.
For instruction fetches, we byte-swap each word read from memory when
writing it into the icache data RAM, and use a tag bit to indicate
whether each cache line contains instructions in BE or LE form.
For data accesses, we simply need to invert the existing byte_reverse
signal in BE mode. The only thing to be careful of is to get the sign
bit from the correct place when doing a sign-extending load that
crosses two doublewords of memory.
For now, interrupts unconditionally set MSR[LE]. We will need some
sort of interrupt-little-endian bit somewhere, perhaps in LPCR.
This also fixes a debug report statement in fetch1.vhdl.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
The tests were using MSR values that did not have MSR_SF or MSR_LE
set. Fix this so that the test still works when 32-bit and BE modes
are implemented.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This is a NiteFury based PCIe M2 form-factor board originally
used for mining. It contains a speed grade 2 Artix 7 200T,
1GB of DDR3 and 32MB of flash.
The serial port is routed to pin 2 (RX) and 3 (TX) of the P2
connector (pin 1 is GND).
Note: Only 16MB of flash is currently usable until code is added
to configure the flash controller to use 4-bytes address commands
on that part.
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To avoid adding too much logic, this moves the adder used by OP_ADD
out of the case statement in execute1.vhdl so that the result can
be used by OP_ADDG6S as well.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
These are no-ops that are reserved for future use as performance
hints, so we just need to treat them as no-ops.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
The addex instruction is like adde but uses the XER[OV] bit for the
carry in and out rather than XER[CA].
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This adds a true random number generator for the Xilinx FPGAs which
uses a set of chaotic ring oscillators to generate random bits and
then passes them through a Linear Hybrid Cellular Automaton (LHCA) to
remove bias, as described in "High Speed True Random Number Generators
in Xilinx FPGAs" by Catalin Baetoniu of Xilinx Inc., in:
https://pdfs.semanticscholar.org/83ac/9e9c1bb3dad5180654984604c8d5d8137412.pdf
This requires adding a .xdc file to tell vivado that the combinatorial
loops that form the ring oscillators are intentional. The same
code should work on other FPGAs as well if their tools can be told to
accept the combinatorial loops.
For simulation, the random.vhdl module gets compiled in, which uses
the pseudorand() function to generate random numbers.
Synthesis using yosys uses nonrandom.vhdl, which always signals an
error, causing darn to return 0xffff_ffff_ffff_ffff.
This adds an implementation of the darn instruction. Darn can return
either raw or conditioned random numbers. On Xilinx FPGAs, reading a
raw random number gives the output of the ring oscillators, and
reading a conditioned random number gives the output of the LHCA.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
These instructions use major opcode 4 and have a third GPR input
operand, so we need a decode table for major opcode 4 and some
plumbing to get the RC register operand read.
The multiply-add instructions use the same insn_type_t values as the
regular multiply instructions, and we distinguish in execute1 by
looking at the major opcode. This turns out to be convenient because
we don't have to add any cases in the code that handles the output of
the multiplier, and it frees up some insn_type_t values.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This also removes OP_MCRXR, as the mcrxr instruction was removed in
version 3.0B of the Power ISA, having been phased-out for the server
architecture since v2.02.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Boris Shingarov