152 lines
3.3 KiB
ArmAsm
152 lines
3.3 KiB
ArmAsm
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//
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// Official Kernal routine, described in:
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//
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// - [RG64] C64 Programmer's Reference Guide - page 285
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// - [CM64] Compute's Mapping the Commodore 64 - page 238
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//
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// CPU registers that has to be preserved (see [RG64]): none
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//
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IOINIT:
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//
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// First initialize the CPU port, to make sure we have correct memory map
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//
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// We want BASIC and KERNAL ROMs mapped, and datasette motor off
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// (https://www.c64-wiki.com/wiki/Zeropage)
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// Work around for VICE bug: Writing $00 before $01 results in rubbish in $01
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// after. https://sourceforge.net/p/vice-emu/bugs/1057/
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ldx #$27
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stx CPU_R6510
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ldx #$EF
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stx CPU_D6510 // [CM64] page 4
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//
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// Now prevent the CIAs from generating interrupts, who knows what damage they can do
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//
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// Disable IRQ generation for both CIAs - see [CM64], page 149
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ldx #$7F
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stx CIA1_ICR // $DC0D
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stx CIA2_ICR // $DD0D
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// See discussion here:
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// https://www.lemon64.com/forum/viewtopic.php?t=41744&sid=e294c254db2ba671cde643f100aae341
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// It seems that initializing this register to $7F is the best idea - UDTIM key scanning
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// also leaves this at $7F
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stx CIA1_PRA // $DC00
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//
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// Now silence the SID chip(s), depending on the configuration - we want them silent ASAP
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//
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// First the standard chip (skip if it is covered by whole $D4XX range)
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lda #$00
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#if !CONFIG_SID_D4XX
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sta SID_SIGVOL
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#endif // !CONFIG_SID_D4XX
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// Silence manually configured 2nd and 3rd SIDs
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#if CONFIG_SID_2ND
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sta SID_SIGVOL - __SID_BASE + CONFIG_SID_2ND_ADDRESS
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#endif // CONFIG_SID_2ND
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#if CONFIG_SID_3RD
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sta SID_SIGVOL - __SID_BASE + CONFIG_SID_3RD_ADDRESS
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#endif // CONFIG_SID_3RD
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// Silence whole D4XX and D5XX ranges (if configured)
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#if CONFIG_SID_D4XX || CONFIG_SID_D5XX
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ldy #$00
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!:
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#if CONFIG_SID_D4XX
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sta SID_SIGVOL + $000, Y
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#endif // CONFIG_SID_D4XX
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#if CONFIG_SID_D5XX
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sta SID_SIGVOL + $100, Y
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#endif // CONFIG_SID_D4XX
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tya
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clc
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adc #$20
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tay
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bne !-
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#endif // CONFIG_SID_D4XX || CONFIG_SID_D5XX
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//
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// Now continue the CIAs initialization
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//
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// For CIA #1 we need port A as output and port B as input to scan the keyboard
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ldx #$FF
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stx CIA1_DDRA // $DC02
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inx
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stx CIA1_DDRB // $DC03
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stx CIA2_DDRB // $DD03 // XXX this port is used for RS-232, value here is most likely wrong!
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#if CONFIG_KEYBOARD_C65 || CONFIG_KEYBOARD_C65_CAPS_LOCK
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lda #$02
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sta C65_EXTKEYS_DDR // output for most keys, input for CAPS LOCK bit
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#endif
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// Set DDR on CIA2 for IEC bus, VIC-II banking (see [CM64], $DDOO description on page 193)
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lda #$3F
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sta CIA2_DDRA // $DD02
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// XXX detect TOD clock, see https://codebase64.org/doku.php?id=base:efficient_tod_initialisation
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// XXX how to initialize these timers???
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// stx CIA1_CRB // $DC0F
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// stx CIA2_CRA // $DD0E
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// stx CIA2_CRB // $DD0F
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// Set VIC-II bank - at least the 'Operacja Proboszcz' game needs this within IOINIT
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// Checked on original ROMs, that it sets bit #2 (RS-232 output) high
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ldx #%00000111 // XXX adapt this to IEC idle state, JMP at the end won't be needed
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stx CIA2_PRA // $DD00
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//
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ldy #<16421
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ldx #>16421
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sty CIA1_TIMALO // $DC04
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stx CIA1_TIMAHI // $DC05
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// Enable timer A to run continuously (http://codebase64.org/doku.php?id=base:timerinterrupts)
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ldx #$11
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stx CIA1_CRA // $DC0E
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// Enable timer interrupt
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ldx #$81
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stx CIA1_ICR // $DC0D
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#if CONFIG_IEC
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// Set IEC bus to its initial idle state
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jmp iec_set_idle
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#else
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rts
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#endif
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