English Amiga Board - View Single Post - FPIAR not updated on unsupported FPU instruction?

Toni Wilen · 14 January 2021, 20:52

FPIAR being updated or not and exception type does not seem to be that simple with 68060..

It seems to partially decode addressing mode first, for example unimplemented instruction will still generate normal F-line without modifying FPIAR if addressing mode is impossible (for example F<xx>.B An,FPx). But there was also some weird situations that need more testing, for example F<implemented>.X Dn,FPx which seems to work strangely. (But I have already noticed 68060 can work very strangely if instruction is "impossible", for example FMOVEM.X #imm,FPx-FPy does not generate exceptions and also zeroes listed FP registers!. So perhaps it is best to not attempt to emulate it perfectly and simply ignore "impossible" conditions)

I also confirmed FMOVECR always updates FPIAR.

14 January 2021, 20:52	#7
Toni Wilen WinUAE developer Join Date: Aug 2001 Location: Hämeenlinna/Finland Age: 49 Posts: 26,502	FPIAR being updated or not and exception type does not seem to be that simple with 68060.. It seems to partially decode addressing mode first, for example unimplemented instruction will still generate normal F-line without modifying FPIAR if addressing mode is impossible (for example F<xx>.B An,FPx). But there was also some weird situations that need more testing, for example F<implemented>.X Dn,FPx which seems to work strangely. (But I have already noticed 68060 can work very strangely if instruction is "impossible", for example FMOVEM.X #imm,FPx-FPy does not generate exceptions and also zeroes listed FP registers!. So perhaps it is best to not attempt to emulate it perfectly and simply ignore "impossible" conditions) I also confirmed FMOVECR always updates FPIAR.