2407e662a9
- rtl/w11a - pdp11.vhd: add cpustat_type in_vecflow - pdp11_sequencer.vhd: BUGFIX: get correct PS after vector push abort - tools - tcode/cpu_details.mac: add test A3.5 - tcode/cpu_mmu.mac: add test C2.5, C2.6, C2.7 - xxdp/ekbee1_patch_1170.scmd: fix test 122 - xxdp/ekbee1_patch_w11a.tcl: fix test 122
2.0 KiB
ECO-036: Get correct PS after vector push abort (2022-12-11)
Scope
- was in w11a since 2009
- affects: all w11a systems
Symptom summary
Test 124 of ekbee1 fails with
SSRA PS RESTORE(1) DOESN'T GET TO RACK E63
OR E63(5) BAD
ERRORPC TEST NUMBER
077344 000124
Analysis
The test makes page 6 non-resident, sets SP to a location in page 6, and
executes a TRAP instruction. The TRAP vector flow fails at the 1st stack
push, a fatal error is detected, an emergency stack is set up (SP := 4)
and a vector 4 flow is started. On an 11/70, such a restarted vector flow
will push the PS and PC seen at the entry of the initial aborted vector
flow, and therefore restore the PS which was already overwritten by the
value read during the vector fetch phase of the initial vector flow.
The w11 did not perform such a recovery and pushed the PS fetched in the
initial vector flow. Correct handling of this case is essential for the MMR0
instruction complete functionality, which is not yet available but will be
implemented in a later release.
Fixes
The 11/70 uses a microcode branch and dedicated states to recover PS in the
case of re-entry into the vector flow.
w11 uses a new cpu_state flag in_vecflow instead.
The current PS is saved in register DTMP when a vector flow is started
with do_start_vec, and later read from DTMP in state s_vec_pushps when
the first vector push is started. do_start_vec is executed in the states
that start a vector flow with a branch to s_vec_getpc.
The new state flag in_vecflow is set in the state s_vec_getpc and cleared
in s_vec_pushpc_w when the last push was successful.
In do_start_vec, the PS is only written to DTMP when in_vecflow is not
set. The pushed PS in a re-entered vector flow comes therefore from the
first entry.
Hindsight
This deficit had no impact on OS operation and had therefore low priority. However, the goal of the w11 is to be an as precise as feasible replica of the 11/70, and it was overdue to fix this.