ROADMAP K1, the packed player's one open structural item. A frame is a picture
AND a palette, and no run in this tree had pointed a DMA channel at the palette
registers. dmagate.s runs 7-9, gated by dma_run.sh and check.sh:
7. 512 B off the disc into $E82000, bus held -- byte-exact in 256 register
words, read back OUT OF the registers by the 68000;
8. the SAME transfer aimed at RAM -- byte-exact at $2C000, and 256 of 256
palette words still read the poison the CPU wrote, which is what attributes
run 7 to the channel's MAR rather than to the readback path;
9. ONE array-chained start across two kinds of destination -- the palette and
six picture rows at the 1,024 B line stride, 2,048 B byte-exact.
So a packed frame is one channel start: a 193-entry array, palette first, CPU
halted from the first byte to the last. The array is scene-constant, because
the packed layout spends both 256-colour pages and there is no page to flip.
What is left on the CPU per frame in the video path is the channel start and the
READ(10) -- no per-frame PAINT, which is not the same claim as no per-frame CPU.
The destination is POISONED first (62.1). Runs 4-6 wrote into RAM that was zero
and GVRAM that was stale against a record that is mostly pad; "it matches the
disc" was weaker than it read as. The host counts whether the poison actually
discriminates instead of assuming it: 511 of 512, and the gate refuses under 500.
And it opened a hardware item (62.4, ROADMAP B4). MAME maps the palette to
palette_device over memory_array, whose write16 is a plain COMBINE_DATA -- RAM
that honours mem_mask, with no handler that could refuse a byte write. Unlike
GVRAM's 256-colour arm there is nothing here to be wrong about, so the run
bounds the model and not the board. What a real palette register does with a
byte write is unmeasured. A negative costs 0.28% of a frame and nothing else.
29_packed_player.py now also prints the two rows with the per-frame palette
charged -- 55.7% of a frame on the chain, 582 KB/s -- alongside the picture-only
figures the codec comparison is quoted against.
check.sh ALL GREEN before (tmp/check_s30_start.log) and after
(tmp/check_s30_end.log).
Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
prosolis
07f36c2af9