> On 6 Feb, 2019, at 7:10 pm, Eddy Nivens <[email protected]> wrote: > > I agree with you re: F-line instructions being reserved for [math] > co-processors but the Mac IIci, though, had a built-in 68882 math > co-processor (FPU) on the motherboard. Is it possible that the OP has an > upgraded IIci with a 68LC040 upgrade card (non-FPU ‘040) and this is causing > the error?
The 68K architecture defines eight coprocessors, all accessed through opcodes of the form 0xFxxx - the three bits immediately following the first F define *which* coprocessor is involved. The 68882 occupies only one of these slots, while IIRC the MMU built into the '030 or '040 occupies another. Referencing any of the other six will cause an F-line trap, as will executing an instruction undefined in the selected coprocessor. FPU emulators can hook into the F-line traps to compensate (slowly) for a missing FPU, as in the LC040, or for unimplemented instructions as in the full '040 (which lacks the transcendental functions in hardware, but has really fast basic functions compared to the '882). The System for '040 Macs includes the latter library, at least, for backwards compatibility. In principle the same mechanism could be used to extend the 68K instruction set using software libraries, but I'm unaware of anyone actually doing that. So a program running off into the weeds is entirely likely to execute a random F-line instruction which traps, even on a machine with a full 68882 installed. This would of course not occur on an operating system with protected memory; you'd get a protection trap instead. - Jonathan Morton -- -- ----- You received this message because you are a member of the Vintage Macs group. The list FAQ is at http://lowendmac.com/lists/vintagemacs.shtml and our netiquette guide is at http://www.lowendmac.com/lists/netiquette.shtml To post to this group, send email to [email protected] To leave this group, send email to [email protected] For more options, visit this group at http://groups.google.com/group/vintage-macs Support for older Macs: http://lowendmac.com/services/ --- You received this message because you are subscribed to the Google Groups "Vintage Macs" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
