Bug 513

Summary:	nmutil.extend.exts not being used in modsw
Product:	Libre-SOC's first SoC	Reporter:	Luke Kenneth Casson Leighton <lkcl>
Component:	Source Code	Assignee:	Jacob Lifshay <programmerjake>
Status:	RESOLVED FIXED
Severity:	enhancement	CC:	libre-soc-bugs
Priority:	High
Version:	unspecified
Hardware:	PC
OS:	Linux
NLnet milestone:	---	total budget (EUR) for completion of task and all subtasks:	0
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Bug Depends on:
Bug Blocks:	383

Description Luke Kenneth Casson Leighton 2020-10-06 13:48:37 BST

http://lists.libre-soc.org/pipermail/libre-soc-dev/2020-October/000721.html

reported that it is a nmigen bug that sign-extension is not being respected.
this is technically incorrect.  because nmigen does not have this capability
it is *our* reponsibility to call the utility function nmutil.extend.exts
until such time as nmigen adds the capability to do what nmutil.extend.exts
does.

Comment 1 Luke Kenneth Casson Leighton 2020-10-06 13:50:18 BST

putting the priority up a bit on this one as we're supposed to be under
a functionality code-freeze (bar optional icache/dcache)

Comment 2 Jacob Lifshay 2020-10-06 13:57:48 BST

nmigen totally can sign extend if the lhs of an assignment is a signed Signal, the workaround I previously added passes the tests:
https://git.libre-soc.org/?p=soc.git;a=commitdiff;h=18a56dd9d9b2c1566b460aacb0d9679bac3e4ccf

nmigen's bug was using the lhs signedness instead of the rhs signedness to decide if it should sign or zero extend.