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unk6502_st2xxx.cpp: More BIOS notes

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AJR 2020-08-12 09:26:24 -04:00
parent 2ec0464575
commit f36df9216a
1 changed files with 5 additions and 1 deletions
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src/mame/drivers/unk6502_st2xxx.cpp
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@ -9,10 +9,14 @@
// these games were ported to unSP hardware at some point, see generaplus_gpl_unknown.cpp
// BIOS calls are made very frequently to the undumped firmware.
// The most common call ($6058 in bbl380, $6062 in ragc153 & dphh8630) seems to involve downloading a snippet of code from Flash and executing it from RAM.
// The most common call ($6058 in bbl380, $6062 in ragc153 & dphh8630) seems to involve downloading a snippet of code from Flash and executing it from RAM at $0300.
// A variant of this call ($60d2 in bbl380, $60e3 in ragc153 & dphh8630) is invoked with jsr.
// For these calls, a 24-bit starting address is specified in $82:$81:$80, and the length in bytes is twice the number specified in $84:$83.
// ST2205U cannot execute code directly from Flash, but has a built-in DMA-compatible NAND interface on Port F ($05).
// The XOR used on ragc153 & dphh8630 is likely performed by the DMA controller.
// $6003 performs a table lookup, depositing a sequence of data at $008e.
// $6000 generates some duration of delay based on the X register.
// One other BIOS call ($6975 in bbl380, $69d2 in ragc153) has an unknown purpose.
#include "emu.h"