掌機 - GP2X Wiz - Assembly - UART

UART0_TX連接到GPIOA-8
UART0_RX則是有專屬接收腳位(不須配置)


UART架構


暫存器


Baudrate計算


使用UART開機模式時，Clock固定使用PLL1且速度為147.46MHz

UART clock = (PLL clock) / (Uart Clock Divisor)

UARTCLKDIV = 40
UART clock = 147.46MHz / 40 = 3.6864MHz

BDR = (3686400 / (115200 * 16)) - 1 = 1

main.s

    .global _start

    .equiv GPIOC_OUT,      0xc000a080
    .equiv GPIOC_OUTENB,   0xc000a084
    .equiv GPIOC_PAD,      0xc000a098
    .equiv GPIOA_ALTFN0,   0xc000a020
    .equiv UART_LCON0,     0xc0016000
    .equiv UART_UCON0,     0xc0016002
    .equiv UART_FCON0,     0xc0016004
    .equiv UART_MCON0,     0xc0016006
    .equiv UART_TRSTATUS0, 0xc0016008
    .equiv UART_THB0,      0xc0016010
    .equiv UART_BRD0,      0xc0016014
    .equiv UART_CLKENB0,   0xc0016040
    .equiv UART_CLKGEN0,   0xc0016044

    .arm
    .text
_start:
    b reset
    b .
    b .
    b .
    b .
    b .
    b .
    b .
    
reset:
    ldr r0, =GPIOC_OUTENB
    ldr r1, =(1 << 16)
    str r1, [r0]

    ldr r0, =GPIOA_ALTFN0
    ldr r1, =(1 << 16)
    str r1, [r0]

    ldr r0, =UART_CLKENB0
    ldr r1, [r0]
    bic r1, #4
    str r1, [r0]

    ldr r0, =UART_LCON0
    ldr r1, =0x83
    strh r1, [r0]

    ldr r0, =UART_UCON0
    ldr r1, =5
    strh r1, [r0]

    ldr r0, =UART_FCON0
    ldr r1, =6
    strh r1, [r0]

    ldr r0, =UART_MCON0
    ldr r1, =0xc0
    str r1, [r0]

    ldr r0, =UART_BRD0
    ldr r1, =1
    strh r1, [r0]

    ldr r0, =UART_CLKGEN0
    ldr r1, =0x272
    strh r1, [r0]

    ldr r0, =UART_FCON0
    ldr r1, =1
    strh r1, [r0]

    ldr r0, =UART_CLKENB0
    ldr r1, [r0]
    orr r1, #4
    str r1, [r0]

    ldr r0, =GPIOC_OUT
    ldr r1, =(1 << 16)
    str r1, [r0]

    ldr r0, =GPIOC_PAD
0:
    ldr r1, [r0]
    tst r1, #(1 << 5)
    bne 0b

    ldr r0, =GPIOC_OUT
    ldr r1, =~(1 << 16)
    str r1, [r0]

    ldr r0, =UART_THB0
    ldr r2, =hello
    ldr r3, =UART_TRSTATUS0
1:
    ldr r1, [r3]
    tst r1, #(1 << 1)
    beq 1b
    ldrb r1, [r2]
    strb r1, [r0]
    add r2, #1
    cmp r1, #0
    bne 1b

    b .

    .align
hello: .asciz "Hello, world!"
    .end

完成