Commit Graph

854 Commits (97478796433decf8f771bece251fc1f9630a3517)
 

Author SHA1 Message Date
Paul Mackerras fb5115c944 FPU: Decide on A input selection a cycle earlier
This moves opsel_a into the reg_type record, meaning that the A
multiplexer input now needs to be decided a cycle earlier.  This helps
timing by eliminating the combinatorial path from r.state and other
things to opsel_a and thence to in_a and result.

This means that some things now take an extra cycle, in particular
some of the exception cases such as when one or both operands are
NaNs.  The NaN handling has been moved out to its own state, which
simplifies the logic for exception cases in other places.  Additions
or subtractions where FRB's exponent is smaller than FRA's will
also take an extra cycle.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras b0b3c0dc70 FPU: Add comments specifying the expectation of r.shift for each state
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras dc1544db69 FPU: Implement floating multiply-add instructions
This implements fmadd, fmsub, fnmadd, fnmsub and their
single-precision counterparts.  The single-precision versions operate
the same as the double-precision versions until the final rounding and
overflow/underflow steps.

This adds an S register to store the low bits of the product.  S
shifts into R on left shifts, and can be negated, but doesn't do any
other arithmetic.

This adds a test for the double-precision versions of these
instructions.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras c083b9507d FPU: Implement ftdiv and ftsqrt
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras c350bc1f25 FPU: Implement fsqrt[s] and add a test for fsqrt
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>
4 years ago
Paul Mackerras 394f993e75 FPU: Implement frsqrte[s] and a test for frsqrte
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>
4 years ago
Paul Mackerras e1bbb786c0 tests/fpu: Add tests for fsel and fcmpu
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 49f3d1e77a FPU: Implement fcmpu and fcmpo
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 4cd9301da6 FPU: Implement fsel
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 4ad5ab9203 FPU: Implement fre[s]
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>
4 years ago
Paul Mackerras 9cce936251 FPU: Implement fdiv[s]
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>
4 years ago
Paul Mackerras e6a5f237bc FPU: Implement fmul[s]
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>
4 years ago
Paul Mackerras 86b826cd7e FPU: Implement fadd[s] and fsub[s] and add tests for them
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 4807d0bdb6 FPU: Implement fmrgew and fmrgow and add tests for them
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 0ad2aa3014 FPU: Implement floating round-to-integer instructions
This implements frin, friz, frip and frim, and adds tests for them.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 03d1aa968a FPU: Implement floating convert to integer instructions
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>
4 years ago
Paul Mackerras 36130f1db3 tests/fpu: Add tests for frsp
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 34b5d4a7b5 FPU: Implement the frsp instruction
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>
4 years ago
Paul Mackerras 9e8fb293ed FPU: Implement floating convert from integer instructions
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>
4 years ago
Paul Mackerras b628af6176 FPU: Implement fmr and related instructions
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>
4 years ago
Paul Mackerras cb27353f37 tests/fpu: Test remaining FPSCR-related instructions
This adds tests for mffsce, mffscrn, mffscrni, mffsl, mcrfs, mtfsfi,
mtfsb0 and mtfsb1.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras fc2968f132 FPU: Implement remaining FPSCR-related instructions
This implements mcrfs, mtfsfi, mtfsb0/1, mffscr, mffscrn, mffscrni and
mffsl.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras bf1d9e9531 tests/fpu: Add tests for basic FPSCR function and interrupt generation
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>
4 years ago
Paul Mackerras 856e9e955f core: Add framework for an FPU
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>
4 years ago
Paul Mackerras 76ec1a2f0a tests/fpu: Add tests for lfs and stfs instructions
This exercises the single-to-double and double-to-single conversions,
including denormalized cases.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 9d285a265c core: Add support for single-precision FP loads and stores
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>
4 years ago
Paul Mackerras bcac4b9b2f tests: Add a test for FP loads and stores
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>
4 years ago
Paul Mackerras 45cd8f4fc3 core: Add support for floating-point loads and stores
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>
4 years ago
Paul Mackerras e1672ea709 tests: Add a test for trace interrupts
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras b589d2d472 execute1: Implement trace interrupts
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>
4 years ago
Paul Mackerras 6a80825e70 decode1: Avoid overriding fields of v.decode in decode1
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>
4 years ago
Michael Neuling da4be71bd3
Merge pull request #239 from paulusmack/master
Implement BE and 32b modes
4 years ago
Paul Mackerras e7a08f33eb tests: Add a test for the load-reserve and store-conditional instructions
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>
4 years ago
Paul Mackerras eee90a0815 loadstore1: Generate alignment interrupts for unaligned larx/stcx
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>
4 years ago
Paul Mackerras 371fd4cc20 tests: Add tests for 32-bit and big-endian modes
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 033ee909fd core: Implement 32-bit mode
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>
4 years ago
Paul Mackerras 2e7b371305 core: Implement big-endian mode
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>
4 years ago
Paul Mackerras 3edc95eea5 tests/mmu: Update to use correct MSR values
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>
4 years ago
Michael Neuling 6d6cf59bb7
Merge pull request #235 from paulusmack/master
More instructions and a random number generator
4 years ago
Michael Neuling 741b2e42ac
Merge pull request #236 from ozbenh/targets
Add support for Genesys2 and Acord CLE-215
4 years ago
Boris Shingarov 679c547e5f fpga: Add support for Genesys2
Signed-off-by: Boris Shingarov <shingarov@labware.com>
4 years ago
Benjamin Herrenschmidt dbb137437c acorn: Add support for the Acorn CLE 215+
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>
4 years ago
Michael Neuling d200733252
Merge pull request #229 from ozbenh/litedram
Litedram: Misc improvements and support for different DRAM geometries
4 years ago
Paul Mackerras 83816cb9e3 core: Implement BCD Assist instructions addg6s, cdtbcd, cbcdtod
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>
4 years ago
Paul Mackerras 7052ceef4a core: Implement the wait instruction as a no-op
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago
Paul Mackerras 7246bd6f67 core: Implement the reserved no-op instructions
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>
4 years ago
Paul Mackerras 5fafdc56ef core: Implement the addex instruction
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>
4 years ago
Paul Mackerras 1a7aebeef8 Add random number generator and implement the darn instruction
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>
4 years ago
Paul Mackerras 290b05f97d core: Implement the maddhd, maddhdu and maddld instructions
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>
4 years ago
Paul Mackerras 8edfbf638b core: Implement the cmpeqb and cmprb instructions
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
4 years ago