This moves the negation of negative operands for signed divide and
modulus operations out of the decode2 stage and into the divider.
If either of the operands for a signed divide or modulus operation
is negative, the divider now takes an extra cycle to negate the
operands that are negative.
The interface to the divider now has an 'is_signed' signal rather
than a 'neg_result' signal, and the dividend and divisor can be
negative, so divider_tb had to be updated for the new interface.
The reason for doing this is that one of the worst timing violations
on the Arty A7-100 at 100MHz involved the carry chain in the adders
that did the negation of the dividend and divisor in the decode stage.
Moving the negations to a separate cycle fixes that and also seems to
reduce the total number of slice LUTs used.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This adds a divider unit, connected to the core in much the same way
that the multiplier unit is connected. The division algorithm is
very simple-minded, taking 64 clock cycles for any division (even
32-bit division instructions).
The decoding is simplified by making use of regularities in the
instruction encoding for div* and mod* instructions. Instead of
having PPC_* encodings from the first-stage decoder for each of the
different div* and mod* instructions, we now just have PPC_DIV and
PPC_MOD, and the inputs to the divider that indicate what sort of
division operation to do are derived from instruction word bits.
Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
This module adds some simple core controls:
reset, stop, start, step
along with icache clear and reading the NIA and core
status bits
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org
We only need two write ports for load with update instructions.
Having two write ports just for this instruction is expensive.
For now we will force them to be the only instruction in the
pipeline, and take two cycles of writeback.
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
It simulated fine, but didn't synthesize. Fix some obvious issues
to get us going again.
Fixes: 9fbaea6f08 ("Rework CR file and add forwarding")
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
Right now we continually print all 3 possible GPRs an instruction
may be using. Add signals so we only print GPRs when they are
actually read. This should hopefully optimise away when synthesized.
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
Handle the CR as a single field with per nibble enables. Forward any
writes in the same cycle.
If this proves to be an issue for timing, we may want to revisit
this in the future. For now, it keeps things simple.
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
The decode2 stage was spaghetti code and needed cleaning up.
Create a series of functions to pull fields from a ppc instruction
and also a series of helpers to extract values for the execution
units.
As suggested by Paul, we should pass all signals to the execution
units and only set the valid signal conditionally, which should
use less resources.
Signed-off-by: Anton Blanchard <anton@linux.ibm.com>
Paul Mackerras
Anton Blanchard