Add simple USART test program

Signed-off-by: Sergey Kiselev <skiselev@gmail.com>

diff --git a/software/tests/test_usart_echo.asm b/software/tests/test_usart_echo.asm
new file mode 100644 (file)
index 0000000..947eabf
--- /dev/null
+++ b/software/tests/test_usart_echo.asm
@@ -0,0 +1,65 @@
+; USART registers\r
+USART_DATA:    EQU     00h\r
+USART_CMD:     EQU     01h\r
+\r
+START:         LXI     H,0C000h\r
+               SPHL\r
+               CALL    USART_INIT\r
+\r
+; write a banner\r
+               MVI     A,38h   ; '8'\r
+               MOV     C,A\r
+               CALL    USART_OUT\r
+               MVI     A,30h   ; '0'\r
+               MOV     C,A\r
+               CALL    USART_OUT\r
+               MVI     A,38h   ; '8'\r
+               MOV     C,A\r
+               CALL    USART_OUT\r
+               MVI     A,35h   ; '5'\r
+               MOV     C,A\r
+               CALL    USART_OUT\r
+               MVI     A,0Dh   ; CR\r
+               MOV     C,A\r
+               CALL    USART_OUT\r
+               MVI     A,0Ah   ; LF\r
+               MOV     C,A\r
+               CALL USART_OUT\r
+\r
+LOOP:          CALL USART_IN\r
+               MOV C,A\r
+               CALL USART_OUT\r
+               JMP LOOP\r
+\r
+USART_INIT:    MVI A,00h\r
+; Set USART to command mode - configure sync operation, write two dummy sync characters\r
+               OUT USART_CMD\r
+               OUT USART_CMD\r
+               OUT USART_CMD\r
+; Issue reset command\r
+               MVI A,40h\r
+               OUT USART_CMD\r
+; Write mode instruction - 1 stop bit, no parity, 8 bits, divide clock by 16\r
+               MVI A,4Eh\r
+               OUT USART_CMD\r
+; Write command instruction - activate RTS, reset error flags, enable RX, activate DTR, enable TX\r
+               MVI A,37h\r
+               OUT USART_CMD\r
+; Clear the data register\r
+               IN USART_DATA\r
+               RET\r
+\r
+; Read character from USART\r
+USART_IN:      IN      USART_CMD       ; Read USART status\r
+               ANI     02h             ; Test RxRdy bit\r
+               JZ      USART_IN        ; Wait for the data\r
+               IN      USART_DATA      ; Read character\r
+               RET\r
+\r
+; Write character to USART\r
+USART_OUT:     IN      USART_CMD\r
+               ANI     01h             ; Test TxRdy\r
+               JZ      USART_OUT       ; Wait until USART is ready to transmit\r
+               MOV     A,C\r
+               OUT     USART_DATA      ; Write character\r
+               RET\r