Separate kernel code from test code

Eventually I want the kernel to be loaded from the SD card as well, but
it still needs to separate from user programs.

At some point there should be a folder just for the BIOS, which should
read from the boot block of the SD card and start executing, and thats
it.

sw/kernel/devices/uart.s

@@ -0,0 +1,36 @@
+.include "io.inc65"
+
+.importzp sp, sreg
+
+.export _uart_txb, _uart_txb_block
+.export _uart_rxb
+.export _uart_status
+
+.autoimport	on
+
+.code
+
+; @in A: byte to transmit
+; Transmits a byte over the UART
+_uart_txb:
+        sta UART_TXB        ; Just write value, don't wait
+        rts
+
+_uart_txb_block:
+        pha
+        sta UART_TXB        ; Write value
+@1:     lda UART_STATUS     ; Wait for status[0] to be 0
+        bit #$01
+        bne @1
+        pla
+        rts
+
+_uart_rxb:
+        lda UART_RXB        ; Read value
+        ldx #$00
+        rts
+
+_uart_status:
+        lda UART_STATUS
+        ldx #$00
+        rts