50 lines
1.6 KiB
ArmAsm
50 lines
1.6 KiB
ArmAsm
// Resources describing the C64 reset sequence:
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// https://www.c64-wiki.com/wiki/Reset_(Process)
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hw_entry_reset:
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// The GPL program at https://github.com/Klaus2m5/6502_65C02_functional_tests/blob/master/6502_functional_test.a65
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// uses the similar initial reset sequence, affirmed by c64 PRG p269
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sei // disable the interrupts, as fast as possible - they are disabled in case of HW reset,
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// but this routine can be also called manually
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ldx #$00
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sta VIC_SCROLX // turn the display off - we want as little screen artifacts as possible
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cld // required for all CPUs - due to possibility of manual call
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dex // $FF - to initialize stack pointer
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txs
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// The following routine is based on reading the public KERNAL jumptable routine
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// list, and making unimaginative assumptions about what should be done on reset.
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// Also, https://codebase64.org/doku.php?id=base:assembling_your_own_cart_rom_image was used
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// as it shows example startup sequence, to be followe by cartridge creators
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// C64 PRG p269
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jsr cartridge_check
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bne !+
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jmp (ICART_COLD_START)
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!:
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// Initialising IO is obviously required. Also indicated by c64 prg p269.
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jsr JIOINIT
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// Setting up the screen and testing ram is obviously required
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// also affirmed by p269 of c64 prg
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jsr JRAMTAS // called RANTAM on Codebase64 wiki
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// Resetting IO vectors is obviously required, if we want interrupts to run
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// also affirmed by c64 prg p269
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jsr JRESTOR
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// "Compute's Mapping the 64" p236
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jsr JCINT
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// What do we do when finished? A C64 jumps into the BASIC ROM
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cli // allow interrupts to happen
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// c64 prg p269
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jmp (IBASIC_COLD_START)
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