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[/] [zipcpu/] [trunk/] [rtl/] [core/] [cpuops.v] - Rev 209

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209 8b bytes, + formal verification throughout + dcache dgisselq 993d 01h /zipcpu/trunk/rtl/core/cpuops.v
205 Updating core to current/best version, to include dblfetch support and full CIS support dgisselq 1713d 13h /zipcpu/trunk/rtl/core/cpuops.v
201 RTL files for the 8-bit capable ZipCPU. dgisselq 1732d 10h /zipcpu/trunk/rtl/core/cpuops.v
193 These changes make it so the ALU multiplies pass a test-bench. dgisselq 1858d 10h /zipcpu/trunk/rtl/core/cpuops.v
175 Fixed the carry bit for logical shifts: it is the last bit shifted out of the
register. 0x80000000>>32 yields a 0 with carry set. Anything logically
shifted by a number greater than thirty two clears carry and register.
dgisselq 1907d 08h /zipcpu/trunk/rtl/core/cpuops.v
138 This updates the CPU multiply instruction into a set of three instructions.
MPY is a 32x32-bit multiply instruction, returning the low 32-bit result,
MPYUHI returns the upper 32-bits assuming the result was unsigned and MPYSHI
returns the upper 32-bits assuming the result was signed.
dgisselq 2039d 13h /zipcpu/trunk/rtl/core/cpuops.v
133 Changes preceding an instruction set update, which will change the multiply
operation from a 16x16 bit multiply to three types of 32x32-bit multiplies.
dgisselq 2054d 04h /zipcpu/trunk/rtl/core/cpuops.v
80 Bug fix: declared the (combined) multiply to be signed again. Also
changed the name of the generate'd for block, to keep ISE from complaining.
dgisselq 2164d 04h /zipcpu/trunk/rtl/core/cpuops.v
71 This contains a bunch of bug fixes. (A lot ...) For example, the pipeline
stall code has also seriously changed, to fixed the pipeline memory load/op
stage conflict, while maintaining no-stall operation for operands that don't
need an offset. This had a cascading effect, however, so that the multiply
could no longer complete in a single cycle. Therefore, the timing on the
multiplies was slowed down to two cycles from a single cycle. (It's the
only two-cycle ALU operation ...) The illegal instruction code has also been
fixed, so that illegal instructions no longer stalls the prefetch bus.
dgisselq 2169d 08h /zipcpu/trunk/rtl/core/cpuops.v
69 This implements the "new Instruction Set" architecture for the Zip CPU. It's
a massive change set, that touches just about everything but probably not
enough of everything. Please see the spec.pdf for a description of this
new architecture.
dgisselq 2175d 12h /zipcpu/trunk/rtl/core/cpuops.v
62 Simplified the subtraction logic, so the carry bit no longer depends on
a separate 32-bit operation but becomes part of the subtract operation.
dgisselq 2236d 12h /zipcpu/trunk/rtl/core/cpuops.v
56 Here's a bit of work in progress for getting the Zip CPU working on a XuLA2
board. Many changes include: the existence of a cpudefs.v file to control
what "options" are included in the ZipCPU build. This allows build control
to be separated from the project directory (one build for a XuLA2 board,
another for a Basys-3 development board). Other changes have made things
perhaps harder to read, but they get rid of warnings from XST.

A big change was the addition of the (* ram_style="distributed" *) comment
for the register set. This was necessary to keep XST from inferring a block
RAM and breaking the logic that was supposed to take place between a register
read and when it was used.
dgisselq 2246d 15h /zipcpu/trunk/rtl/core/cpuops.v
25 Lots of changes, hopefully all for the better. The result works in a
simulator, although it has yet to be tested yet in an FPGA--so it may still
have Xilinx build errors.

1. The wires brought from the CPU to the Zip System for the debug command
register were adjusted. They now include GIE and SLEEP, but no longer include
the step or break enable bits as these were fairly useless anyway.

2. The user and master A-Stall counters were re-labeled as instruction count
counters (which is what they are now anyway). This is for performance reasons
so that, after the fact, you can measure how many instructions per clock
you were actually able to achieve.

3. The CPU debug access port stall was adjusted so that the data port no longer
stalls when the CPU isn't halted. This can be useful, for example, when trying
to determine where th program counter is at without stalling the CPU. (You'll
still need to read two registers, the supervisor and user program counters, and
reading these registers still requires a write to the debug command port first,
so this still requires 4 single operand wishbone bus cycles.)

4. Signed and unsigned 16-bit multiply capabilities were added to the ALU
(cpuops.v) and support added in the Zip CPU master file as well.

5. The ZIP CPU now spports the TRAP bit in the CC register, so that after a user
interrupt the supervisor can tell that it was a user interrupt versus a hardware
interrupt. This bit is set any time the user disables the GIE bit, and cleared
any time the supervisor sets the GIE bit.

6. A reserved position was created in the CC register for a floating point
enable flag. This flag is permanently false, however, on the current
implementation as it doesn't implement floating point.

7. Logic was added to handle the break instruction. This instruction has now
been tested successfully in the simulator. If a break is issued, the CPU will
either halt (if in supervisor mode, or if in user mode with the break enable
bit set in the CC register), or the CPU will trip an interrupt for the
supervisor to transfer execution to a user-level debugging task.

8. After watching the CPU stall on a LDIHI followed by an LDILO, logic was
adjusted to keep the pipeline from stalling in thesee conditions. This lew
logic works for an 'A' operand, or equivalently for a 'B' operand with no
immediate. In the cases of such logic, the operand is loaded directly from the
output of the ALU into the input of the ALU skipping the operand read stage of
the pipelinle. This logic has not been tested on an FPGA yet, so it isn't clear
if it will break timing requirements or not. (Goal is 100 MHz clock.) As
of this new change, the CPU can now execute 0.48 instructions per clock, versus
the 0.44 it was getting before, across the test set.

9. Sleep logic was adjusted to prevent the user from switching to supervisor
mode and putting the processor to (infinite) sleep at the same time. The
justification was the fact that a user should not be able to halt the CPU when
other processes that might want it might still exist.

Other changes were made as well, but to other portions of the project. Those
will be checked in shortly.
dgisselq 2298d 03h /zipcpu/trunk/rtl/core/cpuops.v
15 Updated the core CPUOPS module to make certain that the carry was properly
set on right shifts. (Carry is then the last bit shifted out to the right,
and has no relation to the high order bits of the word.) Also fixed a bug
in the busdelay.v file that prevented our Quad SPI flash controller from
working. (This bug fix has not yet been tested ...) Our test.S program, the
closest thing we have to a regression test and found in the sw/zasm directory,
still successfully passes in Verilator.
dgisselq 2307d 16h /zipcpu/trunk/rtl/core/cpuops.v
12 Bunch of changes while trying to get a hello world program:
1. Right shifts by 32 or more now result in zero, or all of the top bit in the
case of ASRs.
2. zdump now properly includes addresses with dumped lines.
3. zparser now properly handles immediate values via the .DAT instruction.
dgisselq 2322d 08h /zipcpu/trunk/rtl/core/cpuops.v
3 Rebuilt the pipefetch (instruction fetch/cache module) so that it will
let go of the bus if the memory unit wants it to execute an instruction.
Pipefetch will then grab the bus back whtn the memory unit is done, so things
otherwise continue as they were before.

Other tweaks were made to try to reduce code complexity.
dgisselq 2323d 13h /zipcpu/trunk/rtl/core/cpuops.v
2 An initial load. No promises of what works or not, but this is where the
project is at.
dgisselq 2324d 07h /zipcpu/trunk/rtl/core/cpuops.v

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