synth: add SYNTH_MOCK_LARGE_MEMORIES

[oharboe]

@povik Is there a reasonable way to implement such a SRAM mocking feature?

[povik]

@oharboe Is memory_set a hypothetical command?

[povik]

I see there are other dreamed up commands. Let me see if this can be implemented using real commands

[oharboe]

Yes. In ChatGPT's defense it did say that it dreamt up these commands and then it looked for alternatives.

[povik]

I offer this for testing:

memory_collect
foreach path [tee -q -s result.string select -list t:\$mem_v2] {
	set index [string first "/" $path]
	set module [string range $path 0 [expr {$index - 1}]]
	set instance [string range $path [expr {$index + 1}] end]

	set width [rtlil::get_param -uint $module $instance WIDTH]
	set size [rtlil::get_param -uint $module $instance SIZE]
	set nbits [expr $width * $size]
	puts "Memory $path has dimensions $size x $width = $nbits"
	if {$nbits > $::env(SYNTH_MEMORY_MAX_BITS)} {
		rtlil::set_param -uint $module $instance SIZE 1
		puts "Shrunk memory $path from $size rows to 1"
	}
}

[oharboe]

@povik Mysterious error:

make DESIGN_CONFIG=designs/sky130hd/microwatt/config.mk synth

7. Executing MEMORY_COLLECT pass (generating $mem cells).
aminfr' which is not allowed in RTLIL identifiers string '$paramod$5409023ed62e51a90c7a1a5e2fb5908f52c323ea
Command exited with non-zero status 1
Elapsed time: 0:25.30[h:]min:sec. CPU time: user 25.08 sys 0.16 (99%). Peak memory: 149052KB.
make[1]: *** [Makefile:262: do-yosys] Error 1
make: *** [Makefile:272: results/sky130hd/microwatt/base/1_2_yosys.v] Error 2

[povik]

I've found the message template in Yosys. It warns about a special character but at the same time it prints the string containing the special character without escaping hence the mangled output.

log_error("Found control character or space (0x%02x) in string '%s' which is not allowed in RTLIL identifiers\n", *c, p);

I'll take a look to see how to fix the script.

[oharboe]

@povik Purely for my planning purposes, how long do you think you'll need to see if there's a fix for this PR? Days, weeks, months?

If it is very far out, then I think I should close the issue and re-open when we have what we need.

[povik]

@oharboe a day or two