Pace the ring, then read the DMAC config out of the IPL ROM: audio is cheap and the disk is not
Two sessions that were never separated in the working tree, so they land as one commit. check.sh ALL GREEN before and after both. SESSION 19 -- the ring rig gets a frame clock (FINDINGS 51). src/player/stream.s had no frame clock: it asked for record i the instant it finished i-1, outran any finite pipe, and never let the ring back up. The 49.1 sweep passing at 48 KB was therefore a wrap-correctness result and nothing else. PACE/PACEON ($18034/$18038) hold the decoder to 12 fps, so FR_HEAD-FR_TAIL finally means what it reads as: whole frames the decoder could still draw with delivery stopped dead. PACEON=0 free-runs and is what the wrap gate still uses, so every figure in 49 is unmoved. Paced, on the gate container: 64 KB holds 2 frames, 256 KB holds 7-8, 512 KB holds 14-15, all pixel-exact. Tolerance is ceiling-1, measured by cutting the pipe: 256 KB buys 500 ms of dead pipe, not 583. SLACK IS ACCUMULATED, NOT OWNED. It is built out of pipe-wire and a seek spends all of it. At 488 KB/s a 256 KB ring needs 4.83 s of play to reach its ceiling from empty; 512 KB needs 8.42 s to reach 14. A bigger ring raises the ceiling AND lengthens the climb, so a branch point does not ask "is the buffer big enough" but "has there been enough play since the last one" -- and Dragon's Lair's decision points are seconds apart. The rig now also says WHICH resource is binding: at 460 KB/s every ring from 192 KB to 512 KB is rate-bound at ceiling 4 and never fills, so larger rings are dead RAM in that scene. 20_seek_slack.py is the same model rewritten in Python from record sizes, sharing no code with the Lua producer: 35/35 ceilings inside its bracket. SESSION 20 -- the DMAC configuration was in the IPL ROM the whole time (FINDINGS 52). ROADMAP's "do this first" was to put the ADPCM stream on the bus. That needs a clocks-per-byte figure for the audio channel, and 11_cpu_budget.py was charging audio the DISK's rate -- 5 clk/B, its own help text calling it "single-address, bus held". Audio was being charged the favourable end of B3, a 242 KB/s open question. It never had to be a guess. The IPL ROM programs all four HD63450 channels itself and MAME boots the rig with it, so 21_iplrom_dmac.py reads the configuration out of the image and decodes the MC68450 fields. Eight (address, expected bytes, meaning) sites; a mismatch or an unknown revision exits non-zero. In check.sh, no emulator, milliseconds. ch3 DCR=$80, OCR=$32: dual address, 8-bit port, cycle steal WITHOUT hold, REQG=10 external request. The DMAC arbitrates once per byte with no burst to amortise the 5..8 + 2 over, so an audio byte is 16..19 clocks, not 5 -- the old debit was 3.2x..3.8x small. And on the bus it is still nothing: 651 B/frame is 1.25%..1.48% of a frame, about 4% of what the decoder leaves. P6's bus risk does not materialise. The unit worry was worth checking and nearly right: 15.6 kHz is 8 MHz/512 = 15,625 samples/s, two 4-bit samples to a byte = 7,812.5 B/s exactly, and AUDIO_KBPS=7.8 is that in decimal kB while the tool multiplied by 1024. THE DISK CHANNEL IS PROGRAMMED IDENTICALLY. ch1 (SASI) is DCR=$80 too, and so is ch0. That is 16..19 clocks per delivered byte, where 42.4 brackets W at 5..12 and 42.5 has W=8 already missing 47/120 frames. The only worked example of a disk DMA configuration on this machine sits above the entire bracket, and at that price nothing fits at any container size. It is not scsiexrom.bin so B3 stays open -- what changed is that a cheap configuration is now the thing that has to be SHOWN. W <= 12 is a requirement on the player's DMAC programming, not a range the hardware hands us, and it is now the largest open number in the project, ahead of the rate. An unforced cross-check fell out: 15_bus_occupancy.py's new W sweep puts W=8 at 105.7% of the frame, agreeing with 42.5's 47/120, from mode histograms and bus clocks respectively, two models sharing no code. Also: ADPCM outranks the disk at the arbiter (CPR 1 against 2), so an audio byte never waits and a video byte does -- relevant to 51's smooth-rate delivery model. README MEDIA. stream.lua gains DLX_SNAP_EVERY=1 (needs DLX_PACE, off by default, on no path check.sh takes) and tools/media/make_readme_media.py turns the PNGs into docs/img/. The stills and both clips are MAME's own screen pixels. Building it turned up something worth recording. 116 of 119 captured frames are pixel-exact against dlx.py; three are TORN -- frame n on top, frame n-1 below the tear line -- because MAME captured the screen while the block loop was partway down it. decode.s writes straight to the displayed page (one display path, 28.1), so a real player tears the same way, and this is the first time that consequence has been visible rather than argued. The script ASSERTS the tear and refuses to build otherwise, rather than trimming three frames and reporting "every frame I kept is exact". Second correction the capture forced: the snapshot fires before frame n is decoded, so the obvious reading is that it holds frame n-1 -- it does not, because MAME renders the screen at the end of the machine frame, by which time the 68000 has finished frame n. 11_cpu_budget.py's "validated to within 1 pt" line is also corrected: the model reads 2..10 pt HIGH and by more as the frame gets harder, which was already true before either session. src/player/decode.s is unchanged; decode.bin is still 1,296 B at the same MD5. Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
This commit is contained in:
prosolis
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/* Headless harness for px68k's GVRAM write and display model.
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*
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* Tests FINDINGS 46.6 -- the packed 1.0 byte/pixel layout -- on a SECOND
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* emulator, the way tools/bench/c68k does for the CPU core. It links px68k's
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* real x68k/gvram.c: the address decode, the CRTC R20 bit-11 buffer-mode write
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* path, the page-byte selection, the scroll wrap and the index-0 transparency
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* test are all px68k's own code, not a reimplementation.
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*
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* What IS glue here, and is declared as such: the ~12 lines of page-ordering
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* from x11/windraw.c's 256-colour case (which page is drawn opaque and which
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* transparent, as a function of the video controller's priority register).
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* windraw.c is SDL-bound and cannot be linked headless, so that dispatch is
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* mirrored. It is quoted verbatim in pick_order() so the mirroring is
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* auditable.
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*
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* GrphPal is set to the IDENTITY, so what lands in Grp_LineBuf is the 8-bit
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* palette INDEX rather than a host pixel. That keeps the harness out of
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* px68k's host-format colour conversion, and it is faithful: px68k's
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* transparency test is on the index (`if (v != 0x00)`), before the lookup.
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*/
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#include <stdio.h>
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#include <stdlib.h>
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#include <string.h>
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#include "common.h"
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#include "gvram.h"
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/* --- the globals gvram.c expects from the rest of px68k -------------------- */
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BYTE CRTC_Regs[48];
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WORD CRTC_FastClrMask;
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DWORD GrphScrollX[4], GrphScrollY[4];
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WORD GrphPal[256];
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BYTE TextDirtyLine[1024];
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DWORD TextDotX, TextDotY;
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DWORD VLINE;
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BYTE Pal_Regs[1024];
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WORD Pal16[65536];
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WORD Ibit, Pal_HalfMask, Pal_Ix2;
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extern BYTE GVRAM[0x80000];
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extern WORD Grp_LineBuf[1024];
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#define W 256
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#define H 256
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/* 68000 word write: two byte writes, high byte first, as the bus does. */
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static void wr16(DWORD adr, WORD v)
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{
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GVRAM_Write(adr, (BYTE)(v >> 8));
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GVRAM_Write(adr + 1, (BYTE)(v & 0xff));
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}
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static void set_r20(WORD r20) /* CRTC R20 = byte pair 0x28/0x29 */
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{
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CRTC_Regs[0x28] = (BYTE)(r20 >> 8);
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CRTC_Regs[0x29] = (BYTE)(r20 & 0xff);
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}
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/* Mirrors x11/windraw.c, 256-colour case:
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*
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* if ( (VCReg1[1]&3) <= ((VCReg1[1]>>4)&3) ) {
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* ... Grp_DrawLine8(1, 1); opaq = 0;
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* ... Grp_DrawLine8(0, opaq);
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* } else {
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* ... Grp_DrawLine8(0, 1); opaq = 0;
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* ... Grp_DrawLine8(1, opaq);
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* }
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*
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* i.e. the first page drawn is OPAQUE (the bottom) and the second is drawn
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* with opaq=0 (the transparent top).
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*/
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static void draw_line(BYTE vcreg1_lo)
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{
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int bottom = ((vcreg1_lo & 3) <= ((vcreg1_lo >> 4) & 3)) ? 1 : 0;
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Grp_DrawLine8(bottom, 1);
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Grp_DrawLine8(bottom ^ 1, 0);
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}
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int main(int argc, char **argv)
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{
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const char *blob = argc > 1 ? argv[1] : "tmp/frame256p.bin";
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const char *out = argc > 2 ? argv[2] : "tmp/gvpack_px68k.raw";
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int packed = !(argc > 3 && !strcmp(argv[3], "--unpacked"));
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BYTE vc1 = (BYTE)(argc > 4 ? strtol(argv[4], NULL, 0) : 0x02);
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/* --nobuffer: run the packed layout WITHOUT CRTC R20 bit 11, to show the
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* bit is load-bearing here and not decoration. */
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int buffer = !(argc > 5 && !strcmp(argv[5], "--nobuffer"));
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int scroll = !(argc > 5 && !strcmp(argv[5], "--noscroll"));
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/* --keepbuffer: leave R20 bit 11 SET while drawing. MAME blanks the
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* graphics layer in that state; does px68k? */
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int keepbuf = (argc > 5 && !strcmp(argv[5], "--keepbuffer"));
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FILE *f = fopen(blob, "rb");
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if (!f) { perror(blob); return 2; }
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static BYTE d[8 + 768 + 256 * 256];
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size_t n = fread(d, 1, sizeof d, f);
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fclose(f);
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int iw = (d[4] << 8) | d[5], ih = (d[6] << 8) | d[7];
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if (n < (size_t)(8 + 768 + iw * ih)) { fprintf(stderr, "short blob\n"); return 2; }
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const BYTE *pix = d + 8 + 768;
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int yoff = (H - ih) / 2;
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const BYTE BLACK = 255;
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#define PIX(y, x) ((y) < yoff || (y) >= yoff + ih ? BLACK : pix[((y) - yoff) * iw + (x)])
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memset(GVRAM, 0, sizeof GVRAM);
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for (int i = 0; i < 256; i++) GrphPal[i] = (WORD)i; /* identity */
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TextDotX = W; TextDotY = H;
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/* 256x256, 256 colours -- the same R20 tools/bench/crtc_mode.lua applies */
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const WORD R20_DISPLAY = 0x0110;
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set_r20(R20_DISPLAY);
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/* page 0 -> scroll sets 0,1; page 1 -> scroll sets 2,3 */
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GrphScrollX[0] = GrphScrollX[1] = 0;
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GrphScrollY[0] = GrphScrollY[1] = 0;
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GrphScrollX[2] = GrphScrollX[3] = (packed && scroll) ? 384 : 0;
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GrphScrollY[2] = GrphScrollY[3] = 0;
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if (packed) {
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if (buffer) set_r20(R20_DISPLAY | 0x0800); /* buffer mode: unmasked */
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for (int y = 0; y < H; y++) {
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DWORD base = 0xC00000 + y * 1024;
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for (int i = 128; i < 512; i++) wr16(base + i * 2, 0);
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for (int i = 0; i < 128; i++)
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wr16(base + i * 2, (WORD)((PIX(y, i + 128) << 8) | PIX(y, i)));
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}
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if (!keepbuf) set_r20(R20_DISPLAY); /* back to display */
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} else {
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/* the ordinary 2.0 B/pixel path, for a control */
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for (int y = 0; y < H; y++) {
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DWORD base = 0xC00000 + y * 1024;
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for (int x = 0; x < W; x++) wr16(base + x * 2, PIX(y, x));
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}
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}
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FILE *o = fopen(out, "wb");
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if (!o) { perror(out); return 2; }
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for (int y = 0; y < H; y++) {
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VLINE = (DWORD)y;
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memset(Grp_LineBuf, 0, sizeof Grp_LineBuf);
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draw_line(vc1);
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static BYTE row[W];
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for (int x = 0; x < W; x++) row[x] = (BYTE)(Grp_LineBuf[x] & 0xff);
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fwrite(row, 1, W, o);
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}
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fclose(o);
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fprintf(stderr, "[GVPACK] px68k model: %s, vcreg1=%02X, bottom page=%d -> %s\n",
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packed ? (buffer ? "PACKED 1.0 B/px" : "PACKED but bit11 OFF")
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: "unpacked 2.0 B/px", vc1,
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((vc1 & 3) <= ((vc1 >> 4) & 3)) ? 1 : 0, out);
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return 0;
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}
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