Add serial driver and irq support

sw/kernel/devices/serial.s

@@ -0,0 +1,94 @@
+.MACPACK generic
+
+.autoimport
+
+.import _enable_irq, _send_eoi, _uart_txb_block
+
+.importzp tmp1, ptr1
+
+.export _serial_init
+.export _serial_handle_irq
+
+.export _serial_putc, _serial_puts, _serial_getc, _serial_get_nb
+
+.zeropage
+
+last_char: .res 1
+
+
+.code
+
+UART        = $efe6
+UART_TXB    = UART
+UART_RXB    = UART
+UART_STATUS = UART + 1
+
+; Initialize Serial Port
+; No initialization needed, just register irq handler.
+.proc _serial_init
+        lda #<_serial_handle_irq
+        ldx #>_serial_handle_irq
+        jsr pushax
+        lda #$01
+        jsr _register_irq
+        stz last_char
+        rts
+.endproc
+
+; Serial Port IRQ Handler
+; Get the character and store it.
+.proc _serial_handle_irq
+        lda UART_RXB
+        sta last_char
+        ora #$80        ; set msb
+        jsr _send_eoi
+        rti
+.endproc
+
+; Serial Port Get Character
+; If a character has not been received, block until one is.
+.proc _serial_getc
+L1:     lda last_char
+        bpl L1
+        and #$7f
+        sta last_char
+        rts
+.endproc
+
+; Serial Port Get Character Non-Blocking
+; return last character, even if it has already been read.
+; If the character is new, we still clear the new flag.
+.proc _serial_get_nb
+        lda last_char
+        bpl L1
+        and #$7f
+        sta last_char
+L1:     rts
+.endproc
+
+
+; Serial Port Put Character
+; send a single character over the serial port.
+.proc _serial_putc
+        jsr _uart_txb_block
+        cmp #$0a
+        bne @1
+        lda #$0d
+        jsr _uart_txb_block
+@1:     rts
+.endproc
+
+; Send a string over the serial port. Needs stlen
+.proc _serial_puts
+        sta ptr1                ; Store pointer in ptr1
+        stx ptr1+1  
+        ldy #$00                ; initialize y to 0
+L1:     lda (ptr1),y            ; load character from string
+        beq L2                  ; Quit if NULL
+        jsr _uart_txb_block      ; send character (does not change y or ptr1)
+        iny                     ; increment y
+        bne L1                  ; If Y == 0, increment high byte of pointer
+        inc ptr1+1
+        bne L1                  ; if high byte wraps around, give up
+L2:     rts
+.endproc