forked from arti/vt1200
arti
636b3d6985
Measured on the unit: byte stores to DRAM 13.92 us, to VRAM 13.93 us -- the same, so the display arbiter is not involved. In MAME 16-bit stores halve the time exactly (863 ms vs 1588 ms per frame), i.e. the cost is per store instruction, not per byte. Against the graphics engine (FILL L 0.40 us/word, PIXBLT L,XY 0.62 us/word) the CPU is 25-35x slower per word. So frames must never be built with CPU stores: the LANCE can chain descriptors so a 160 KB frame lands contiguously in a pre-armed buffer with no CPU copy, and one PIXBLT L,XY puts it on screen. Budget: full frame ~5 fps (129 ms wire + 60 ms blit), 640x512 ~21 fps, 320x240 ~80 fps. Report section 75; cmd 10 (PIXBLT from RAM) and cmd 11 (16-bit store control) are the benchmarks.