z80code/echo.asm at master · andreasjarliden/z80code · GitHub

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.eq PIO_A_DATA 00h
.eq PIO_A_CONTROL 02h
.eq PIO_B_CONTROL 03h
.eq PIO_COMMAND_SET_BIDIRECTIONAL_MODE 8fh
.eq PIO_COMMAND_SET_BIT_MODE 0cfh
.eq INTERRUPT_TABLE F000h
.eq INTERRUPT_VECTOR_0 0F000h
.eq INTERRUPT_VECTOR_2 0F002h
.eq INTERRUPT_VECTOR_4 0F004h
.eq INTERRUPT_TABLE_HIGH 0F0h ; High byte of INTERRUPT_TABLE address
.eq LOAD_ADDRESS 8000h

	ld a, PIO_COMMAND_SET_BIDIRECTIONAL_MODE
	out (PIO_A_CONTROL)

	; Interrupt vector 2 for Output (PIO A)
	ld a, 2
	out (PIO_A_CONTROL)
	; Interrupt vector 4 for Input (PIO B)
	ld a, 4
	out (PIO_B_CONTROL)

; Set PIO Port A in bidirectional mode. Before doing that, Port B
; must be set to bit mode.
	ld a, PIO_COMMAND_SET_BIT_MODE	; Send 11xx (mode 3) | 1111 (set mode) to PIO Control A (IO addr 02h)
	out (PIO_B_CONTROL)
	ld a, 00h		; Next byte to PIO configures Input/Output. Set as all outputs.
	out (PIO_B_CONTROL)

	ld a, 77h		; Disable int, HIGH, AND, Mask follows
	out (PIO_B_CONTROL)
	ld a, 0ffh		; Mask all bits
	out (PIO_B_CONTROL)
	ld a, 83h		; Enable interrupts PIO B (Actually bidir input on port A)
	out (PIO_B_CONTROL)

	ld a, 83h		; Enable interrupts PIO A
	out (PIO_A_CONTROL)

	; Install inputInt and outputInt for interupts 2 and 4
	ld hl, outputInt
	ld (INTERRUPT_VECTOR_2), hl
	ld hl, inputInt	; TODO would like outputInt + LOAD_ADDRESS
	ld (INTERRUPT_VECTOR_4), hl

	; Enable vectored interrupts
	ld a, INTERRUPT_TABLE_HIGH
	ld i, a
	im 2	; Interupt mode 2: vectored interrupts
	ei

	; Read from PIO_A_DATA to activate BRDY to signal that we are ready to read
	in (PIO_A_DATA)
loop:
	halt
	jr loop

; TODO: This needs to be absolute or determined at runtime!
inputInt:
	in (PIO_A_DATA)
	out (PIO_A_DATA)
	ei
	reti

outputInt:
	; TODO on output
	ei
	reti