[OpenPOWER-HDL-Cores] bug in microwatt stfsu and stfdu

Luke Kenneth Casson Leighton lkcl at lkcl.net
Wed May 19 10:19:24 UTC 2021


(blegh, sorry, having difficulty cut/pasting into HTML-formatted message,
to get alignment here)





-- unit fac internal in1 in2 in3 out CR CR inv inv cry cry ldst BR sgn upd
rsrv 32b sgn rc lk sgl rpt
52 => (LDST, FPU, OP_STORE, RA_OR_ZERO, CONST_SI, FRS, NONE, '0', '0', '0',
'0', ZERO, '0', is4B, '0', '0', '0', '0', '1', '0', NONE, '0', '0', NONE),
-- stfs
53 => (LDST, FPU, OP_STORE, RA_OR_ZERO, CONST_SI, FRS, RA, '0', '0', '0',
'0', ZERO, '0', is4B, '0', '0', '1', '0', '1', '0', NONE, '0', '0', NONE),
-- stfsu





v3.0B book I chapter 4 page 145 section 4.6.3 states:

stfs FRS,D(RA)

   if RA = 0 then b <- 0
    else           b <- (RA)
    EA <- + EXTS(D)

but stfsu states simply:

    EA <- (RA) + EXTS(D)

thus we conclude that Major 53 is *wrong*, in1 should simply be RA *not*
RA_OR_ZERO.

now that i'm looking at it, stfdu is also wrong.

stfsx is *correct*.  stfs is correct.  stfd is correct.  stfdux is
*wrong*.  stfdx is correct.

basically needs a full review.  in the above *i'm assuming the spec is
correct*.

l.
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