denise: OCS DENISEID ($07C) floats the undriven bus high to 0xFFFF#122
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The 8362 OCS Denise has no DENISEID register, so a CPU read of $DFF07C reads the undriven custom data bus. That bus floats high, so the read returns 0xFFFF -- and because the low byte (0xFF) is not the 0xFC that the 8373 ECS Denise drives, software still correctly detects OCS. Copperline returned the deterministic-zero undriven-bus fallback instead, so the ID read back as 0x0000 on OCS. Read $07C as the Denise revision id when it drives one (ECS 0xFFFC) and as the float-high 0xFFFF otherwise, and list it as a readable register. vAmigaTS Denise/Misc/Id/deniseid on OCS drops from 39.9% to 0.0% differing pixels against the vAmiga 4.4 reference; ECS is unchanged and the standard demo screenshots stay byte-identical (the change only affects an OCS read of $07C).
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Problem
The 8362 OCS Denise has no DENISEID register, so a CPU read of
$DFF07Creadsthe undriven custom data bus. That bus floats high, so the read returns 0xFFFF
-- and because the low byte (0xFF) is not the 0xFC that the 8373 ECS Denise
drives, software still correctly detects OCS. Copperline returned its
deterministic-zero undriven-bus fallback, so the ID read back as 0x0000 on OCS.
Fix
Read
$07Cas the Denise revision id when it drives one (ECS = 0xFFFC) and asthe float-high 0xFFFF otherwise, and list it as a readable register.
Validation
the vAmiga 4.4 reference (verified with
tools/adf-compare.sh).byte-identical at 5s and 9s (the change only affects an OCS read of
$07C).clippy and fmt clean.