Bug 740

Summary:	sync instruction incorrectly assigned to OP_NOP
Product:	Libre-SOC's first SoC	Reporter:	Jacob Lifshay <programmerjake>
Component:	Source Code	Assignee:	Luke Kenneth Casson Leighton <lkcl>
Status:	CONFIRMED ---
Severity:	major	CC:	libre-soc-bugs, programmerjake
Priority:	---
Version:	unspecified
Hardware:	All
OS:	All
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Description Jacob Lifshay 2021-11-05 21:43:15 GMT

I'm assuming it should be instead assigned to OP_FENCE or similar, but am not changing it right now to not break our code, since treating it as a nop mostly works for a single-core system.

https://git.libre-soc.org/?p=openpower-isa.git;a=blob;f=openpower/isatables/minor_31.csv;h=dcadd41ca276fc3a2046aea5dd505de0702538f5;hb=HEAD#l199

Comment 1 Luke Kenneth Casson Leighton 2021-11-05 22:00:17 GMT

we are copying microwatt verbatim.  microwatt caches are writethru.
therefore sync is inherently a nop.

Comment 2 Jacob Lifshay 2021-11-05 22:14:40 GMT

(In reply to Luke Kenneth Casson Leighton from comment #1)
> we are copying microwatt verbatim.  microwatt caches are writethru.
> therefore sync is inherently a nop.

well, that only works on a single-core system. on a multi-core system, we also need to wait for all in-progress load/stores, and execute a system-wide synchronization of some sort (needed for supporting sequential-consistency atomic thread fences).