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.syntax unified
.cpu cortex-m0plus
.thumb
.equ RESETS_BASE, 0x4000c000
.equ RESET_OFST, 0x0
.equ RESET_DONE_OFST, 0x8
.equ CLOCKS_BASE, 0x40008000
.equ CLK_REF_CTRL_OFST, 0x30
.equ CLK_SYS_CTRL_OFST, 0x3c
.equ CLK_PERI_CTRL_OFST, 0x48
.equ UART0_BASE, 0x40034000
.equ UARTDR_OFST, 0x00
.equ UARTFR_OFST, 0x18
.equ UARTIBRD_OFST, 0x24
.equ UARTFBRD_OFST, 0x28
.equ UARTLCR_H_OFST, 0x2c
.equ UARTCR_OFST, 0x30
.equ ATOMIC_CLEAR, 0x3000
.type setup_uart, %function
.global setup_uart
setup_uart:
// Deassert the reset
ldr r1, =(RESETS_BASE + ATOMIC_CLEAR)
movs r0, 1
lsls r0, 22 // UART0 is bit 22
str r0, [r1, RESET_OFST]
ldr r1, =RESETS_BASE
1:
ldr r2, [r1, RESET_DONE_OFST]
tst r0, r2
beq 1b
// Enable clk_peri
ldr r1, =CLOCKS_BASE
movs r0, 0x80 // use xosc (=0x4 << 5) as clk_ref source
str r0, [r1, CLK_PERI_CTRL_OFST]
// Set the baud rate divisors
movs r0, 6 // integer baud rate = 6
ldr r0, [r1, UARTIBRD_OFST]
movs r0, 33 // fractional baud rate = 33
ldr r0, [r1, UARTFBRD_OFST]
// Enable the FIFOs and set the format
movs r0, 0x70 // word len 8 bits (bits 6:5 = 0b11), bit 4 (FIFO en)
str r0, [r1, UARTLCR_H_OFST]
// Set enable bits in the control register
ldr r1, =UART0_BASE
movs r0, 0x3
lsls r0, 8 // set bits 8 and 9 (TX and RX enable)
adds r0, 0x1 // set bit 0 (UART enable)
str r0, [r1, UARTCR_OFST]
bx lr
uart_send:
ldr r1, =UART0_BASE
poll_TXFF:
ldr r2, [r1, UARTFR_OFST]
movs r3, 0x20 // bit 5 (TX FIFO full)
tst r2, r3
bne poll_TXFF
movs r2, 0xff
ands r0, r2
str r0, [r1, UARTDR_OFST]
bx lr
uart_recv:
ldr r1, =UART0_BASE
poll_RXFE:
ldr r2, [r1, UARTFR_OFST]
movs r3, 0x10 // bit 4 (RX FIFO empty)
tst r2, r3
bne poll_RXFE
ldr r0, [r1, UARTDR_OFST]
bx lr
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