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Add source code of the ROM

Pawel Jablonski authored on 14/12/2022 19:10:08
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rom/src/io.asm
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+; Author: Pawel Jablonski
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+; E-mail: pj@xirx.net
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+; WWW: xirx.net
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+; GIT: git.xirx.net
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+;
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+; License: You can use this code however you like
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+; but leave information about the original author.
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+; Code is free for non-commercial and commercial use.
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+
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+; No arguments
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+; No return
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+global .xIOInit:
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+	push A
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+	push B
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+	push X
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+	; Set counter
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+	mov 0, A
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+	; Set last clock value
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+	mov 0, B
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+	; Wait until IO board is not started
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+.xIOInit_wait:
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+	in X
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+	and 0x10, X
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+	cmp B, X
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+	je .xIOInit_wait
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+	mov X, B
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+	inc A
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+	; Wait until 8 edges are detected
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+	cmp 8, A
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+	jne .xIOInit_wait
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+	pop X
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+	pop B
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+	pop A
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+	ret
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+
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+; Arguments:
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+; 	A - register address
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+; No return
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+global .xIOSetRegister:
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+	push X
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+	push A
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+	; Get bus status bit
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+	in X
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+	and 0x80, X
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+	; Send register address
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+	out 0x00
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+	and 0x0f, A
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+	or 0b11000000, A
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+	out A
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+	; Wait for status change
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+.xIOSetRegister_wait:
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+	in A
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+	and 0x80, A
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+	cmp A, X
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+	je .xIOSetRegister_wait
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+	pop A
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+	pop X
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+	ret
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+
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+; Arguments:
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+; 	A - data to transmit
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+; No return
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+global .xIOWriteLowHalf:
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+	push X
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+	push A
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+	; Get bus status bit
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+	in X
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+	and 0x80, X
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+	; Send low half
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+	out 0x00
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+	and 0x0f, A
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+	or 0b11100000, A
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+	out A
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+	; Wait for status change
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+.xIOWriteLowHalf_wait:
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+	in A
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+	and 0x80, A
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+	cmp A, X
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+	je .xIOWriteLowHalf_wait
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+	pop A
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+	pop X
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+	ret
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+
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+; Arguments:
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+; 	A - data to transmit
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+; No return
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+global .xIOWriteHighHalf:
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+	push X
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+	push A
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+	; Get bus status bit
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+	in X
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+	and 0x80, X
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+	; Send high half
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+	out 0x00
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+	swap A
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+	and 0x0f, A
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+	or 0b11110000, A
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+	out A
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+	; Wait for status change
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+.xIOWriteHighHalf_wait:
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+	in A
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+	and 0x80, A
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+	cmp A, X
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+	je .xIOWriteLowHalf_wait
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+	pop A
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+	pop X
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+	ret
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+
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+; No arguments
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+; No return
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+global .xIOWrite:
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+	call .xIOWriteLowHalf
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+	call .xIOWriteHighHalf
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+	ret
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+
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+; No arguments
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+; Return:
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+; 	A - received data
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+global .xIOReadLowHalf:
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+	; Push registers to stack
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+	push X
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+	push B
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+	push A
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+	in X
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+	and 0x80, X
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+	; Read low half
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+	out 0x00
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+	and 0x0f, A
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+	or 0b10100000, A
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+	out A
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+	; Wait for status change
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+.xIOReadLowHalf_wait:
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+	; Get bus status bit
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+	in A
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+	mov A, B
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+	and 0x80, A
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+	; Wait until status bit is not toggled
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+	cmp A, X
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+	je .xIOReadLowHalf_wait
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+	; Set low half to return
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+	and 0x0f, B
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+	pop A
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+	and 0xf0, A
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+	or B, A
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+	pop B
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+	pop X
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+	ret
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+
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+; No arguments
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+; Return:
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+; 	A - received data
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+global .xIOReadHighHalf:
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+	push X
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+	push B
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+	push A
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+	; Get bus status bit
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+	in X
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+	and 0x80, X
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+	; Read high half
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+	out 0x00
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+	and 0x0f, A
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+	or 0b10110000, A
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+	out A
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+	; Wait for status change
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+.xIOReadHighHalf_wait:
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+	; Get bus status bit
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+	in A
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+	mov A, B
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+	and 0x80, A
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+	; Wait until status bit is not toggled
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+	cmp A, X
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+	je .xIOReadHighHalf_wait
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+	; Set high half to return
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+	swap B
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+	and 0xf0, B
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+	pop A
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+	and 0x0f, A
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+	or B, A
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+	pop B
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+	pop X
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+	ret
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+
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+; No arguments
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+; No return
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+global .xIORead:
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+	call .xIOReadLowHalf
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+	call .xIOReadHighHalf
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+	ret
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+