From 9f3e4fe03aac841c2ae5440752046ad73065d23e Mon Sep 17 00:00:00 2001 From: AJR Date: Sat, 1 Oct 2022 23:16:47 -0400 Subject: mn1880: Additional notes --- src/devices/cpu/mn1880/mn1880.cpp | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/src/devices/cpu/mn1880/mn1880.cpp b/src/devices/cpu/mn1880/mn1880.cpp index 9ea47debcb0..0a23b988918 100644 --- a/src/devices/cpu/mn1880/mn1880.cpp +++ b/src/devices/cpu/mn1880/mn1880.cpp @@ -64,6 +64,17 @@ contents of locations about to be written to may show misleading values. Likewise, PCs at which watchpoint hits occur may be incorrectly reported for writes. + * Due to the pipelining of writes, an interrupt may be accepted during + an instruction which attempts to disable interrupts by setting the + IEMASK bit, which may be cleared insted when control reaches the next + sequential instruction from a RETI. This sequencing glitch is + documented in the MN187XX23 user's manual, along with a failsafe way + of setting IEMASK, and similar workarounds in extant program code + suggest it is likewise present in the MN1880 series. + * The optional MMU, which expands the memory spaces in certain models + which contain neither internal ROM nor RAM, has been emulated only + to the extent required by psr500, though it likely has a few other + features and quirks. ***************************************************************************/ -- cgit v1.2.3