github.com/wfjm.w11
1
0
Fork 0
mirror of https://github.com/wfjm/w11.git synced 2026-02-14 04:04:42 +00:00
Code Issues Releases Wiki Activity

docu and comment updates [skip ci]

Browse Source
This commit is contained in:
wfjm
2023-01-04 08:46:30 +01:00
parent 6831d1cda5
commit 146dc4d56a
13 changed files with 184 additions and 46 deletions
Download Patch File Download Diff File Expand all files Collapse all files

18
doc/simh_diff_ser_forced_fetch.md Normal file
View File

@@ -0,0 +1,18 @@
## Known differences between SimH, 11/70, and w11a
### SimH: No unconditional instruction fetch after stack error abort
The 11/70 suppresses the recognition of _break requests_ at the end of
a vector flow of a stack error abort. The processor manual states
> 6.2.2.3 Timing of Stack Error Aborts
> BRQ STROBE is thus inhibited, not only during ZAP.00, but also during
> SVC.90, thus guaranteeing the execution of the first instruction of the
> error subroutine before any other error can be processed.
The rationale behind was apparently to ensure that the handler, which
is called with `SP=0` pointing to an emergency stack, can set up a new
stack before any other condition interferes.
SimH does not implement this behavior, nor does w11.
Beyond that, it would be very difficult to verify this extreme corner case.