395 lines
8.8 KiB
NASM
395 lines
8.8 KiB
NASM
STACK_TOP = 0xFFFF
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DELAY_LOOPS_PER_MS = 40
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BANK_CONTROL_PORT = 0x00
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BOOT_BANK_MAPPING = 0x06 ; ROM on, banking on, upper 16K at C000-FFFF
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ROM_DISABLE_BIT = 0x01
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BANK_SELECT_BIT = 0x02
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BANK_ENABLE_BIT = 0x04
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BANK_MODE_CLEAR_MASK = 0xF9 ; preserve ROM-disable and auxiliary outputs
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.include "bios.inc"
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.globl _main
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.globl _delay_ms
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.globl _io_out
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.globl _io_in
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.globl _enable_interrupts
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.globl _disable_interrupts
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.globl _jump_to
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.globl _bios_putc
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.globl _bios_try_getc
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.globl _bios_getc
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.globl _bios_init
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.globl _bios_bank
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.globl _bios_rom_disable
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.globl _bios_rom_enable
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.globl _bank_control_shadow
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.globl resident_image_end
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.globl s__DATA
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.globl l__DATA
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.globl s__INITIALIZER
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.globl s__INITIALIZED
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.globl l__INITIALIZER
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.area _BOOT (ABS)
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.org 0x00
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jp boot_copy
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.org 0x08
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boot_copy:
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di
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; Keep ROM enabled while mapping the upper physical 16K at C000-FFFF.
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; The resident copy therefore survives either banked mode after boot.
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ld a, #BOOT_BANK_MAPPING
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out (BANK_CONTROL_PORT), a
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ld sp, #STACK_TOP
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ld hl, #RESIDENT_ROM_OFFSET
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ld de, #RESIDENT_RAM_BASE
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ld bc, #(resident_image_end - RESIDENT_RAM_BASE)
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ldir
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jp init
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.area _ITABLE (ABS)
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; The executable vector page is part of the image copied to high RAM.
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.org RESIDENT_RAM_BASE
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jp init
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.org RESIDENT_RAM_BASE + 0x08
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reti
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.org RESIDENT_RAM_BASE + 0x10
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reti
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.org RESIDENT_RAM_BASE + 0x18
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reti
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.org RESIDENT_RAM_BASE + 0x20
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reti
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.org RESIDENT_RAM_BASE + 0x28
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reti
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.org RESIDENT_RAM_BASE + 0x30
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reti
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.org RESIDENT_RAM_BASE + 0x38
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reti
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; IM 2 table: the CTC supplies vectors 40, 42, 44, and 46.
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.org RESIDENT_RAM_BASE + 0x40
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.dw ctc_isr ; CTC channel 0: vector 0x40
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.dw ctc_isr ; CTC channel 1: vector 0x42
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.dw ctc_isr ; CTC channel 2: vector 0x44
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.dw uart_isr ; CTC channel 3: vector 0x46
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; Stable BIOS jump table for ROM-resident applications.
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; C050 putc(A), C053 try_getc(), C056 getc(), C059 io_out(A,L),
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; C05C io_in(A), C05F delay_ms(HL), C062 monitor warm start,
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; C065 bank(A), C068 disable ROM, C06B enable ROM.
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.org BIOS_PUTC
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jp bios_service_putc
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.org BIOS_TRY_GETC
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jp bios_service_try_getc
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.org BIOS_GETC
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jp bios_service_getc
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.org BIOS_IO_OUT
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jp bios_service_io_out
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.org BIOS_IO_IN
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jp bios_service_io_in
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.org BIOS_DELAY_MS
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jp bios_service_delay_ms
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.org BIOS_MONITOR
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jp init
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.org BIOS_BANK
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jp _bios_bank
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.org BIOS_ROM_DISABLE
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jp _bios_rom_disable
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.org BIOS_ROM_ENABLE
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jp _bios_rom_enable
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; Port 00 is write-only. Keep its last BIOS-managed value outside the C data
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; areas so a monitor warm start does not reset it. The bootstrap establishes
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; this same value in the hardware before the resident image is copied.
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.org RESIDENT_RAM_BASE + 0x70
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_bank_control_shadow::
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.db BOOT_BANK_MAPPING
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.area _HOME
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init:
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di
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ld sp, #STACK_TOP
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; A reset may have interrupted a CTC service routine without executing
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; RETI. Release any stale daisy-chain in-service latches before the
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; channels are reinitialized. RETI acts as RET for each CALL while
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; also signalling end-of-interrupt to daisy-chained peripherals.
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call release_daisy_chain
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call release_daisy_chain
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call release_daisy_chain
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call release_daisy_chain
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call gsinit
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; Setup interrupt mode 2
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ld a, #0xC0
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ld i, a
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im 2
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call _bios_init
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call _main
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hang:
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jr hang
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release_daisy_chain:
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reti
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.area _GSINIT
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gsinit:
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ld bc, #l__INITIALIZER
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ld a, b
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or c
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jr z, zero_data
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ld de, #s__INITIALIZED
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ld hl, #s__INITIALIZER
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ldir
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zero_data:
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ld bc, #l__DATA
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ld a, b
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or c
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jr z, gsinit_done
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ld hl, #s__DATA
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xor a
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clear_loop:
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xor a ; BC loop test below changes A
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ld (hl), a
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inc hl
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dec bc
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ld a, b
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or c
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jr nz, clear_loop
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gsinit_done:
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.area _GSFINAL
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ret
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resident_image_end:
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.area _CODE
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; Select a RAM mapping while retaining the shadowed ROM-disable bit.
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; Input: A=0 selects lower 48K + upper 16K; any other value selects upper 64K.
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; Both modes keep banking enabled. A and flags are preserved.
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_bios_bank::
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push af
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or a
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jr z, bios_bank_split
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ld a, (_bank_control_shadow)
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and #BANK_MODE_CLEAR_MASK
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or #BANK_ENABLE_BIT
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jr bios_bank_update
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bios_bank_split:
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ld a, (_bank_control_shadow)
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and #BANK_MODE_CLEAR_MASK
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or #(BANK_ENABLE_BIT | BANK_SELECT_BIT)
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bios_bank_update:
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ld (_bank_control_shadow), a
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out (BANK_CONTROL_PORT), a
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pop af
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ret
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; Hide ROM while preserving the selected RAM mapping.
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; A and flags are preserved.
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_bios_rom_disable::
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push af
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ld a, (_bank_control_shadow)
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or #ROM_DISABLE_BIT
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jr bios_bank_update
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; Make ROM visible again while preserving the selected RAM mapping.
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; A and flags are preserved.
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_bios_rom_enable::
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push af
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ld a, (_bank_control_shadow)
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and #0xFE
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jr bios_bank_update
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; BIOS ABI services preserve registers except documented return values.
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bios_service_putc:
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push af
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push bc
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push de
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push hl
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push ix
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push iy
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call _bios_putc
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pop iy
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pop ix
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pop hl
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pop de
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pop bc
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pop af
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ret
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bios_service_try_getc:
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push bc
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push de
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push hl
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push ix
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push iy
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call _bios_try_getc
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pop iy
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pop ix
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pop hl
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pop de
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pop bc
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ret
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bios_service_getc:
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push bc
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push de
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push hl
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push ix
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push iy
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call _bios_getc
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pop iy
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pop ix
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pop hl
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pop de
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pop bc
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ret
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bios_service_io_out:
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push af
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push bc
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push de
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push hl
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push ix
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push iy
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call _io_out
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pop iy
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pop ix
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pop hl
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pop de
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pop bc
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pop af
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ret
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bios_service_io_in:
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push bc
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push de
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push hl
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push ix
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push iy
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call _io_in
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pop iy
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pop ix
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pop hl
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pop de
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pop bc
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ret
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bios_service_delay_ms:
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push af
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push bc
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push de
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push hl
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push ix
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push iy
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call _delay_ms
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pop iy
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pop ix
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pop hl
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pop de
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pop bc
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pop af
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ret
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.macro MAKE_ISR entry, handler
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.globl handler
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entry:
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push af
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push bc
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push de
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push hl
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push ix
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push iy
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ex af, af'
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push af
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exx
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push bc
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push de
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push hl
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call handler
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pop hl
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pop de
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pop bc
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exx
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pop af
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ex af, af'
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pop iy
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pop ix
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pop hl
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pop de
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pop bc
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pop af
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ei
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reti
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.endm
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MAKE_ISR ctc_isr, _ctc_interrupt
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MAKE_ISR uart_isr, _uart_interrupt
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_enable_interrupts::
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ei
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ret
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_disable_interrupts::
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di
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ret
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; Write a byte to an I/O port.
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; Input: A = port address, L = data byte.
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_io_out::
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ld c, a
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ld a, l
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out (c), a
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ret
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; Read a byte from an I/O port.
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; Input: A = port address.
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; Return: A = data byte.
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_io_in::
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ld c, a
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in a, (c)
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ret
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; Execute code at HL. Because this routine is entered with CALL, a RET in the
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; target returns to the monitor immediately after jump_to().
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_jump_to::
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jp (hl)
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; Approximate millisecond delay.
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; Input: HL = delay in milliseconds.
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_delay_ms::
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ld a, h
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or l
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ret z
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delay_ms_outer$:
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push hl
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ld hl, #DELAY_LOOPS_PER_MS
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delay_ms_inner$:
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dec hl
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ld a, h
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or l
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jr nz, delay_ms_inner$
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pop hl
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dec hl
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ld a, h
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or l
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jr nz, delay_ms_outer$
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ret
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