Put the palette on the channel, and find one start paints a whole frame

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

tools/bench/check.sh

@@ -550,6 +550,16 @@ echo "--- session 27: the DMAC drives the data phase, and holds the bus (FINDING
 #     again, so the run asserts the contrast and not just the held value;
 #   * the channel's own CSR/CER/MTC/MAR, which must say it moved every byte
 #     without error;
+#   * THE PALETTE REGISTERS AT $E82000 (session 30, ROADMAP K1): the same
+#     transfer aimed at the palette, byte-exact into 256 register words read
+#     back by the 68000; the SAME transfer aimed 20 KB away leaving the palette
+#     as the CPU poisoned it, which is what attributes the first run to the
+#     channel's MAR; and ONE array-chained start crossing from the registers
+#     into GVRAM, which is the shape of a whole frame -- a palette entry and
+#     192 row entries, started once. What this does NOT settle is the board:
+#     MAME models the palette as a generic palette_device over memory_array,
+#     whose write16 is a plain COMBINE_DATA, so it cannot tell a register file
+#     that takes byte writes from one that does not (FINDINGS 62.4);
 #   * and a WINDOWED read through the channel REFUSED. 117 of 120 records start
 #     part way into a sector (58.3); a channel writes a contiguous run and cannot
 #     drop the bytes in front of one, so it would write the neighbouring records
@@ -565,7 +575,8 @@ if command -v chdman > /dev/null; then
   bash tools/bench/dma_run.sh "$DLX" > tmp/dma_gate.log 2>&1 || {
     echo "FAIL: the DMAC did not drive the SCSI data phase."
     tail -16 tmp/dma_gate.log; exit 1; }
-  grep -aE "BYTES OK|MTC one instruction|trips round|REFUSED" tmp/dma_gate.log \
+  grep -aE "BYTES OK|MTC one instruction|trips round|REFUSED|PALETTE|ONE START" \
+    tmp/dma_gate.log \
     | sed 's/^ *//;s/^/  /'
 else
   echo "  SKIPPED: no chdman (ships with mame-tools) -- cannot build the volume"