main
2
Commits
| Author | SHA1 | Message | Date | |
|---|---|---|---|---|
 prosolis
|
c419251266 |
Put the frame clock on the 68000, and find that the 12 fps frame does not exist
ROADMAP P3 said "needs MFP timer or VBL" and neither can do it. The MFP's timer clock is 16 MHz/4, its prescalers stop at 200 and its data register is 8 bits, so the slowest tick any single timer can make is 78.125 Hz -- 6.5x faster than a frame -- and 4e6/12 is not an integer, so no setting reaches 12 Hz at all. The raster has no whole divide near 12 either: 4 refreshes is 13.86 fps and 5 is 11.09. tools/analysis/23_frame_clock.py walks all 7x256 timer settings rather than asserting it. src/player/clock.i takes the V-DISP falling edge on MFP GPIP4 -- the start of vertical blanking, which is when a player would present -- and adds fps*VTOTAL per edge to a 16-bit accumulator, emitting a tick at 31,500 and keeping the remainder. The long-run rate is fps*VTOTAL/VTOTAL = 12.000000 fps exactly, and both constants are read out of the CRTC at init, so the clock is derived from the registers that generate the raster it counts. Measured over 3,000 refreshes: 3,000 interrupts, 649 ticks where 649.1429 were due. It costs 181.35 clocks per V-DISP, 838 per frame, 0.1006% of the budget -- timed by the 68000 itself, because the host's granularity is 17.64 ms and the interrupt is microseconds. The loop's own cost was calibrated rather than looked up and landed on 38.000002 clocks, which both licenses the subtraction and confirms buscost.py's model; the 181.35 then decomposes exactly, leaving 43.99 clocks for the interrupt exception -- the textbook 44, measured. THE ONE THAT MOVES SOMETHING: 12 fps on a 55.4577 Hz raster is 4.6215 refreshes, so a frame is shown for 4 refreshes (72.13 ms) or 5 (90.16 ms), 37.9% of them short. The 833,333-clock budget every figure in this project is priced against is the MEAN slot, and the short one is 13.4% under it. The cadence was already in the tree unnamed: stream.lua's tick is sampled at frame boundaries, so its gaps were always 4 or 5, and every host-paced result in FINDINGS 49/51 carried it. P3 moved who produces it onto the machine and made it visible. It is not a dropped frame -- the pace gate lets an overrun eat the next frame's idle -- and on the gate container it costs 4 frames of 120 their idle against 1 for the nominal model, most of that the frame-0 transient at 111% of budget. stream.s counts it now, and the rig matches an offline model of the divider exactly. Also struck: MAME's raster runs 2.22% fast. refresh_mode() builds the frame period from scr.max_x*scr.max_y with scr.max_x = m_htotal - 8, one character cell short and an inclusive bound used as a count, so it runs at 56.6901 Hz where the registers say 55.4577 -- agreeing to six digits with the arithmetic. Every "1/55.46 s granularity" note in this tree was wrong and is 1/56.69 s, corrected in six files with the derivation put once in crtc_mode.lua. No conclusion changes and no 68000 cycle figure moves; the CPU clock is unrelated to the screen. But anything paced by the raster runs fast under MAME, so the rig reports both rates and prices the interrupt against the hardware's. decode.s and frame.i are unchanged; decode.bin is still 1,296 B at the same MD5. The pace gate's wait loop is byte-for-byte the one FINDINGS 51 measured and the free-running path executes none of the new code. check.sh gains two stages: the clock's own measurement, and 120 frames decoded pixel-exact with nothing outside the machine deciding when a frame may start. Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6 |
||
|
prosolis
|
7179339bd2 |
Move the loader onto the 68000, and find 5,920 bytes nobody counted
src/player/load.i expands both codebooks to word-per-pixel form and packs the palette to GGGGGRRRRRBBBBBI out of the RAW container header, byte-exact against tools/bench/dlxload.py on both CPU cores. The palette half is gated on words read back out of the palette registers at $E82000, so "the words reached the hardware" is part of what passes. ROADMAP P1 is done; P2's encoder half (a reserved black entry, 23.4) is not, and is a re-encode rather than an edit. A scene change costs 18.96 ms of 68000 time, 22.8% of one 12 fps frame; boot costs 24.70 ms. The scratch tables describe the CRTC, not the scene, so pal_tables is a separate entry point built once at boot -- 5.29 ms off every scene change. The one that moves something: the scene header is 5,920 B that no rate table in this tree included, because it belongs to no frame record. In FINDINGS 51.3's currency it is divided by the surplus pipe - wire, so it is hypersensitive: 138 ms of extra refill climb at 488 KB/s and 1.099 s at 451.4 KB/s, for the same bytes. tools/analysis/22_scene_load.py prices it across explicit rates. Recorded as open: the two CPU cores agree to <3% on every stage but the table build, where they differ by 16.4%. px68k's C68K charges a flat 50 clocks for MULU/MULS (c68kmacro.h:1869) where the 68000 charges 38+2n, which explains 4,608 of the 8,703 clock gap. 4,095 clocks are unexplained. Nothing else in src/player/ multiplies, so no figure in FINDINGS 24-52 is affected. decode.s and stream.s are untouched; decode.bin is still 1,296 B at the same MD5. check.sh gains a stage that gates byte-exactness on both cores and deliberately does not gate the cycle counts -- MAME's clock is 1/55.46 s and a wall timing would make the green light host-sensitive. Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6 |