mirror of
https://github.com/sehugg/8bitworkshop.git
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93 lines
1.6 KiB
Plaintext
93 lines
1.6 KiB
Plaintext
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.importzp tmp4, ptr3, ptr4
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.import callax
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.export _bankselect
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.export _ramselect
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.export _xramset
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.export _xramwrite
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.export _xramread
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.zeropage
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; current ROM bank index (not used for RAM)
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_currbank: .res 1
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; must be in shared ROM bank
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.code
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;extern void bankselect(char index);
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;#pragma wrapped-call (push, bankselect, 0)
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;#pragma code-name (push, "ROM0")
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;
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; Wrapper function for selecting a ROM bank
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;NOTE: this does not preserve Y
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_bankselect:
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tay
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; save the old bank index
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lda _currbank
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pha
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; select the new bank
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lda tmp4
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sta _currbank
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sta $3F
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tya
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; call the wrapped function
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call_wrapped_and_exit:
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jsr call_wrapped_func
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; restore the previous bank
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pla
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sta _currbank
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sta $3F
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rts
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; Wrapper function for selecting the RAM bank
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; This must be called from a ROM bank, because it
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; will always exit into the last selected ROM bank
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;NOTE: this does not preserve Y
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_ramselect:
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tay
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; save the old bank index
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lda _currbank
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pha
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; select the RAM bank
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lda tmp4
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sta $3E
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lda #0 ; needed for Stella signature?
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tya
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jmp call_wrapped_and_exit
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; Used to do: jsr (ptr4)
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call_wrapped_func:
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jmp (ptr4)
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; Write a byte to address (ptr3) in RAM bank 0
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_xramwrite:
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; select the RAM bank
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ldx #0
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stx $3E
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sta (ptr3,x)
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restore_bank:
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ldx _currbank
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stx $3F
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rts
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; Read a byte to address (ptr4) in RAM bank 0
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_xramread:
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; modify the ptr4
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; select the RAM bank
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ldx #0
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stx $3E
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lda (ptr4,x)
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jmp restore_bank
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; Set the xram read/write address (in ptr3/ptr4)
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_xramset:
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sta ptr4+0
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sta ptr3+0
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stx ptr4+1 ; read
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txa
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ora #%00000100
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sta ptr3+1 ; write
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rts
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