Picoblaze enhencement and assembler

I forgot to say you need Python and also the Ply (Python Lex Yacc) library ...

Hi Sylvain,

Nothing to add but encouragement really. The software offerings for picoblaze are limited, especially in the non-windows world. Both picoasm and kpicosim are very good, but their development seems to have stopped.

If you can get a polished version of your assembler finished, it sounds like it would be a great tool.

Andy

Of course, you're working on the simulator now, right? :)

I think you mean a New Assembler ?

Hmmm - could be dangerous for maintenance. Another scheme is to use '?' or similar prefix to mean local label.

Have you looked at the Lattice Mico8 - Quite similar to the Picoblaze, but more formally opensource, and they have just extended it to make it more 'HLL ready'.

Have a look and see if your opcode extensions can fit into their decode ?

-jg

Yes :) I was careful in the subject but that one slipped.

I've used the same convention as the GNU assembler. I've modelled the syntax after theirs, but making sure it's easy to parse with Lex / YACC. As it was my first lex/yacc experience I didn't want to take too much time to make it work.

Especially since I needed that compiler to ease my work for a commercial project with an approaching dead line :)

I had a look at the Lattrice Mico8. But since my target was Xilinx, the picoblaze seemed like a better choice (smaller and faster ...) I didn't investigate further and just coded this assembler to have an easier time when programming it.

I'm not that interested in HLL because when I uses theses. But a macro preprocessor would be nice :)

Sylvain

I don't think so ... I rarely used the one that are available because the code on the picoblaze is often so dependent on the hw around it that it just doesn't do anything meaning full without it ...

What I did is that my assembler output a symbol table and so in the modelsim you can get it to display :

uart_print_str + 0x00, uart_print_str + 0x01 .... instead of the addesses in the code, and also the variable name instead of address in the scratch pad. Very useful to trace what's going on.

Sylvain

Yes they did a great job and I used those for a some time. But since they respected the Xilinx 'standard' assembly format, they were limited ...

I choose to break compatibility so that I could extend easily. But even without the compatibility, it's pretty easy to convert old software. Mostly a few subsitute with regexp and adding a .text at the start and that should do it :)

Thanks.

I'll try to polish things up a little and maybe write some documentation and so forth.

But I probably won't do a lot of work on it since I changed job and this new one is not related to fpga (nor hw dev) in any way ...

Sylvain

You can use plain old cpp for that purpose. A few months ago I wrote a PLC compiler thingy. I used cpp as a preprocessor for it.

Mmm, I hadn't tought of that. That's a nice easy way to get a well known syntax.

However for an assembler it's nice to have more 'advanced' things. I'm not an expert in the C preprocessor but making a macro that would expand :

STACK_PUSH(s0, s1, s2, s3)

into

store s0, (sp)0 store s1, (sp)1 store s2, (sp)2 store s3, (sp)3 add sp, 4

Seems kinda hard ...

Sylvain

You shouldn't push the limits too far... Your example smells more like assembler extensions than macro's.

You mean something like this -

#define STACK_PUSH(a,b,c,d) store a, (sp)0 store b, (sp)1 store c, (sp)2 store d, (sp)3 add sp, 4

STACK_PUSH(s0, s1, s2, s3)

Mark

:) I meant with a variable number of argument, autoadapting itself.

Sylvain

Yes ... I seem to recall the Microchip PIC assembler supported things like that ...

Sylvain

I don't know the picoblaze procedure/interrupt conventions, but getting an interrupt between store s1 & store s2 or so looks like trouble.

regards, Gerhard

There is no convention ... you just fix what you want for yourself. But indeed, with a classic one, this would be a problem. Solution is to either

- Don't use interrupts :) That actually my case for the sw where this snippet comes from

- Make it a critical zone :

cli store s0, (sp)0 store s1, (sp)1 store s2, (sp)2 store s3, (sp)3 add sp, 4 sti

- Use dual pointer :

add sp, 4 sub bp, sp, 4 store s0, (bp)0 store s1, (bp)1 store s2, (bp)2 store s3, (bp)3

- Have the interrupts with their own dedicated stack and a dedicated reg used only by them. So the interrupt handler would start by .equ si, s14 .bss __isr_stack: .space 32 .text __isr: load si, __isr_stack store sp, (si) load sp, si add sp, 1 store s0, sp(0) ... ...

- Reserve the space 'before' :

add sp, 4 store s0, sp(-4) store s1, sp(-3) store s2, sp(-2) store s3, sp(-1)

Unfortunatly, I don't think my hw mod can extend to allow negative offset without adding some slices ... I'd have to recheck.

Sylvain

This may seem like a minor annoyance to you, but it is one of those things that a user will tire of very quickly... after about one lost file in fact.

Couldn't you fix that so the output file is first or use option flags to indicate the output file such as -o name?