Add basic UART driver

This didn't have a chance to get tested so I hope it works. There is not fancy stuff here, just write to the register and wait till it is done.
2022-03-14 00:24:08 -05:00
parent b48438f6b2
commit 0b5ccf48b8
3 changed files with 46 additions and 1 deletions
--- a/sw/uart.s
+++ b/sw/uart.s
@@ -0,0 +1,29 @@
+.include "io.inc65"
+
+.importzp sp, sreg
+
+.export _uart_txb
+.export _uart_txb_block
+.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:
+        sta UART_TXB        ; Write value
+@1:     lda UART_STATUS     ; Wait for status[0] to be 0
+        bit #$01
+        bne @1
+        rts
+
+_uart_status:
+        lda UART_STATUS
+        ldx #$00
+        rts