98 lines
2.7 KiB
ArmAsm
98 lines
2.7 KiB
ArmAsm
; ---------------------------------------------------------------------------
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; interrupt.s
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; ---------------------------------------------------------------------------
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;
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; Interrupt handler.
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;
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; Checks for a BRK instruction and returns from all valid interrupts.
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.import _handle_irq
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.import _cputc, _clrscr
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.export _irq_int, _nmi_int
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.include "io.inc65"
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.segment "CODE"
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.PC02 ; Force 65C02 assembly mode
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; ---------------------------------------------------------------------------
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; Non-maskable interrupt (NMI) service routine
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_nmi_int: RTI ; Return from all NMI interrupts
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; ---------------------------------------------------------------------------
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; Maskable interrupt (IRQ) service routine
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_irq_int: PHX ; Save X register contents to stack
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TSX ; Transfer stack pointer to X
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PHA ; Save accumulator contents to stack
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INX ; Increment X so it points to the status
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INX ; register value saved on the stack
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LDA $100,X ; Load status register contents
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AND #$10 ; Isolate B status bit
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BNE break ; If B = 1, BRK detected
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; ---------------------------------------------------------------------------
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; IRQ detected, return
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irq: PLA ; Restore accumulator contents
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PLX ; Restore X register contents
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jsr _handle_irq ; Handle the IRQ
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RTI ; Return from all IRQ interrupts
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; ---------------------------------------------------------------------------
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; BRK detected, stop
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break:
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bios_table:
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.addr _console_clear
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.addr _console_read_char
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.addr _console_write_char
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_console_clear:
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jsr _clrscr
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rti
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_console_read_char:
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; not supported
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rti
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_console_write_char:
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jsr _cputc
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rti
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; What functions do we need?
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; UART
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; clear
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; write character
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; read character
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; DISK
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; init (or should it just init on boot?)
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; read sector into memory
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; FS
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; init (if disk init succeeds, should it always try?)
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; find add
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; I think that is all we need for now?
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; How do we call the functions?
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; we have to call `brk` to trigger the interrupt
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; in any of the three registers we can have arguments
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; or we could have them pushed to the stack, assuming
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; the stack is in the same location
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; Or you could pass a pointer which points to an array
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; of arguments
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; for things like clear, read/write character, and init you don't
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; need any arguments.
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; jump table index needs to be in x, but also needs to be a multiple
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; of 2.
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