risc-8 core

[Blackie Beard]

Has anyone here played with Thomas Coonan's risc-8
(free verilog clone of pic16c57 mcu). I wasn't sure, but
simulation of it seems to indicate a bug. I can't seem
to contact Mr. Coonan by his email addresses from his
website (cutting out the anti-spam portion).

I could be wrong, but there seems to be a problem in
the logic for goto. I suppose I could remedy this by
making the first code in any jumpable location to be NOP.

in cpu.v at one point, there is this:
if (skip == 1'b1) begin
inst <= 12'b000000000000; // FORCE NOP

Then later there this comment:
// Remember that the skip instructions work by inserting
// a NOP instruction or not into program stream and don't
// change the PC.

But in the place where the program counter is coded in, there is no
functionality dependant upon the "skip" signal.

My S/W works on MPSim tool. I have a section doing a bit test
which does or doesn't (depending on bit) perform "goto" to three
locations back. The first part within the loop is to read TMR0
into W, then I check whether it's zero, when it's zero I fall out of
the loop. However, the first time through the loop it loads TMR0
into W, but after that a NOP is executed (not in addition to the
movf TMR0 to W reg, but instead of it).

Is it possible that there needs to be some hook in the pc_in block
that will not allow pc to increment if skip is active? Here is the
sequence from the list file, which executes in risc-8 as an endless
loop:

000B 0201 00067 loop movf TMR0, W ; move tmr0 to w
000C 0743 00068 btfss STATUS, Z ; fall out if tmr0 = 0
000D 0A0B 00069 goto loop ; else loop back

Thanks for any insight,
BB

 

[Blackie Beard]

Sorry - disregard all this. I was not aware that the memory
model I replaced has built-in function to latch the address.
So I'll just build that function into my wrapper. I'm excited
to say that I did get this working in Altera EP20K60E part.
A simple program to blink an LED at 1Hz, but it shows that
the S/W code compiled with free Microchip tools is working
in Coonan's verilog synthesizable PIC core.

The PIC16C57 MCU is chosen to act as traffic cop in SoC
project. This is just the fun stuff I do at home, not the
tedious stuff I do at the daily grind (ie. work).

BB