prosolis
34f9ee341d
Session 3 left the harness on the IPL's 768x512 text timing because no CRTC values had been derived and guessing them was the failure mode to avoid. This derives them from MAME 0.277's divisor ladder instead, and the derivation is self-checking: the 256-wide mode runs at div 6 against the 768 mode's div 2, so htotal is exactly 1104/3 = 368 dots and every horizontal register divides by three with no remainder. Only the blanking split rounds. Verified by snapshot: native 256x512, active area pixel-exact, x=512 wrap gone. Two things fell out that change numbers elsewhere: - The palette's shared LSB I must be chosen per entry, not hardcoded to 1. Doing so lifts the display ceiling from 38.85 to 40.81 dB and is the only way to reach true black at all, since pal6bit(1) = 4. 102 of 256 entries want I = 0, so this is not a corner case. Supersedes FINDINGS 22.4; scsi has ~2 dB more headroom than that section claimed. The encoder does not do this yet. - Letterboxing costs a palette entry: GVRAM cleared to zero shows entry 0, and a free mediancut palette puts a real image colour there. 255 colours plus a reserved black, via prep_frame.py --reserve-black. MAME's graphics double-scan is phase-shifted one raster line (it halves the absolute scanline and vbegin is odd), which produced a false failure before it was understood; the regression test now asserts the shifted pairing explicitly. Still Lua-side. No 68000 instruction has drawn a pixel; the 38% blit estimate remains unvalidated. What this buys is a defined geometry for the decoder to write into: 256 words per row, 1024-byte stride, rows 32..223. Claude-Session: https://claude.ai/code/session_01194oWYW8DQXK1SZ2DnChW6
73 lines
2.7 KiB
Lua
73 lines
2.7 KiB
Lua
-- Same as show_frame.lua, but sets a REAL 256x256 CRTC mode instead of
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-- borrowing the IPL's 768x512 text timing. Proves the mode table in
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-- crtc_mode.lua and removes the x=512 wrap of FINDINGS 22.5.
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M=manager.machine; SP=M.devices[":maincpu"].spaces["program"]; SUB=nil
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local function load_mode()
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for _,p in ipairs{"../tools/bench/crtc_mode.lua","tools/bench/crtc_mode.lua","crtc_mode.lua"} do
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local f=loadfile(p); if f then return f() end
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end
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error("crtc_mode.lua not found")
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end
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local MODE = load_mode()
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local GVRAM, GPAL = 0xC00000, 0xE82000
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local f=io.open("frame256.bin","rb"); local d=f:read("a"); f:close()
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local function B(i) return string.byte(d,i) end
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local W,H = B(5)*256+B(6), B(7)*256+B(8)
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local PAL0, PIX0 = 9, 9+256*3
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local YOFF = (MODE.height - H) // 2 -- letterbox 192 rows inside 256
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-- GGGGGRRRRRBBBBBI, confirmed from x68k_v.cpp. The LSB "I" is SHARED by all
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-- three channels: each renders as pal6bit((field<<1)|I). Hardcoding I=1 (as
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-- show_frame.lua does) makes true black unreachable -- pal6bit(1) = 4 -- so I
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-- is chosen per entry to minimise summed squared error over R,G,B.
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local function pal6(v) return ((v<<2)|(v>>4)) & 0xff end
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local function pack(r,g,b)
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local f = {r>>3, g>>3, b>>3}
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local best, bestI = nil, 1
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for I=0,1 do
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local e=0
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for c=1,3 do
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local want = ({r,g,b})[c]
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local d = pal6((f[c]<<1)|I) - want
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e = e + d*d
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end
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if best==nil or e<best then best,bestI = e,I end
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end
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return (f[2]<<11)|(f[1]<<6)|(f[3]<<1)|bestI
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end
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local function T() local t=M.time; return t.seconds+t.attoseconds/1e18 end
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local st,tp="wait",nil
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SUB = emu.add_machine_frame_notifier(function()
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local t=T()
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if st=="wait" then
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if t<3.0 then return end
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MODE.apply(SP)
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-- clear the letterbox rows: GVRAM holds IPL leftovers, not zeros
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for y=0,MODE.height-1 do
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if y<YOFF or y>=YOFF+H then
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local base=GVRAM+y*1024
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for x=0,MODE.width-1 do SP:write_u16(base+x*2,0) end
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end
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end
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for c=0,255 do
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local o=PAL0+c*3
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SP:write_u16(GPAL+c*2, pack(B(o),B(o+1),B(o+2)))
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end
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for y=0,H-1 do
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local row,base = PIX0+y*W, GVRAM+(y+YOFF)*1024
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for x=0,W-1 do SP:write_u16(base+x*2, B(row+x)) end
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end
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print(string.format("[256] R00-R08 %d %d %d %d %d %d %d %d %d R20=%04X yoff=%d t=%.3f",
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SP:read_u16(0xE80000),SP:read_u16(0xE80002),SP:read_u16(0xE80004),SP:read_u16(0xE80006),
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SP:read_u16(0xE80008),SP:read_u16(0xE8000A),SP:read_u16(0xE8000C),SP:read_u16(0xE8000E),
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SP:read_u16(0xE80010),SP:read_u16(0xE80028), YOFF, t))
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st,tp="painted",t
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elseif st=="painted" and t>tp+0.30 then
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M.video:snapshot(); print("[256] snapshot"); st="done"; M:exit()
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end
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end)
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