[Libre-soc-dev] daily kan-ban update 01sep2020
Luke Kenneth Casson Leighton
lkcl at lkcl.net
Tue Sep 1 16:46:26 BST 2020
you are not going to believe what the bug is that has gone unnoticed for 5
months in CR handling.
the simulator constructs fields from the operand such as BC, FXM and so
on. these are bit-accessible via slices so it is possible to do BO and
CR tests are usually done "if CR[BC+32] " and of course BC, being 5 bits,
goes into a SelectableInt of size 5, because the BC field in the opcode is
5 bits. this has the unintended sideeffect of making any operations modulo
any number plus 32 modulo 32 (because it of course fits into 5 bits) is the
on and off i must have been hunting for this bug for 5 days.
i have an interim "adequate" hack/solution that will do the job. the
"correct" solution is to do the arithmetic at the correct bitwidth or
convert to integers.
crowd-funded eco-conscious hardware: https://www.crowdsupply.com/eoma68
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