1 files changed, 65 insertions, 0 deletions
diff --git a/assembler/uart.s b/assembler/uart.s
new file mode 100644
index 0000000..b845c8b
--- /dev/null
+++ b/assembler/uart.s
@@ -0,0 +1,65 @@
+.syntax unified
+.cpu cortex-m0plus
+.thumb
+
+.equ UART0_BASE, 0x40034000
+.equ UARTDR_OFST,     0x00
+.equ UARTFR_OFST,     0x18
+
+.type uart_send, %function
+.global uart_send
+
+uart_send:
+  ldr r1, =UART0_BASE
+  movs r3, 0b1 << 5 // TX FIFO full
+1:
+  ldr r2, [r1, UARTFR_OFST]
+  tst r2, r3
+  bne 1b
+  strb r0, [r1, UARTDR_OFST]
+  bx lr
+
+.type uart_recv, %function
+.global uart_recv
+
+uart_recv:
+  ldr r1, =UART0_BASE
+  movs r3, 0b1 << 4 // RX FIFO empty
+1:
+  ldr r2, [r1, UARTFR_OFST]
+  tst r2, r3
+  bne 1b
+  ldrb r0, [r1, UARTDR_OFST]
+  bx lr
+
+.type send_hex, %function
+.global send_hex
+
+send_hex:
+  push {lr}
+  movs r4, r0
+  movs r0, '0
+  bl uart_send
+  movs r0, 'x
+  bl uart_send
+  movs r5, 8 // eight nibbles in a word
+0:
+  movs r0, 28 // rotate left 4
+  rors r4, r0
+  movs r0, 0xF // lowest nibble mask
+  ands r0, r4
+  cmp r0, 0x9 // number or letter?
+  bhi 1f
+  adds r0, '0
+  b 2f
+1:
+  adds r0, ('A - 0xA)
+2:
+  bl uart_send
+  subs r5, 1
+  bne 0b
+  movs r0, '\r
+  bl uart_send
+  movs r0, '\n
+  bl uart_send
+  pop {pc}