掌機 - TRIMUI - Assembly - UART

參考資料：
http://nano.lichee.pro/
https://mangopi.org/mangopi_r

UART1腳位位於PA2、PA3


位址


暫存器


Baudrate計算方式

PLL = 24MHz*N*K/M

0x80041800:
  K = 1
  M = 1
  N = 24

PLL_PERIPH = 24MHz*25 = 600MHz
AHB_CLK = PLL_PERIPH/(AHB_PRE_DIV*AHB_CLK_DIV_RATIO) = 600MHz/(3*1) = 200MHz
APB_CLK = AHB_CLK/APB_CLK_RATIO = 200MHz/2 = 100MHz

0x00003180:
  AHB_PRE_DIV = 3
  APB_CLK_RATIO = 2
  AHB_CLK_DIV_RATIO = 1

Baudrate = APB_CLK/(16*divisor) = 100MHz/(16*54) = 115741 ~= 115200

main.s

    .global _start

    .equiv CCU_BASE,              0x01c20000
    .equiv GPIO_BASE,             0x01c20800
    .equiv UART1_BASE,            0x01c25400

    .equiv PLL_PERIPH_CTRL_REG,   0x0028
    .equiv AHB_APB_HCLKC_CFG_REG, 0x0054
    .equiv BUS_CLK_GATING_REG2,   0x0068
    .equiv BUS_SOFT_RST_REG2,     0x02d0

    .equiv PA,        (0x24 * 0) 
    .equiv PORT_CFG0, 0x00
    .equiv PORT_DATA, 0x10
    .equiv UART_RBR,  0x0000
    .equiv UART_DLL,  0x0000
    .equiv UART_DLH,  0x0004
    .equiv UART_IER,  0x0004
    .equiv UART_IIR,  0x0008
    .equiv UART_LCR,  0x000c
    .equiv UART_MCR,  0x0010
    .equiv UART_USR,  0x007c

    .arm
    .text
_start:
    .long 0xea000016
    .byte 'e', 'G', 'O', 'N', '.', 'B', 'T', '0'
    .long 0, __spl_size
    .byte 'S', 'P', 'L', 2
    .long 0, 0
    .long 0, 0, 0, 0, 0, 0, 0, 0
    .long 0, 0, 0, 0, 0, 0, 0, 0

_vector:
    b reset
    b .
    b .
    b .
    b .
    b .
    b .
    b .

reset:
    ldr r0, =CCU_BASE
    ldr r1, =0x80041800
    str r1, [r0, #PLL_PERIPH_CTRL_REG]
    ldr r1, =0x00003180
    str r1, [r0, #AHB_APB_HCLKC_CFG_REG]

    ldr r0, =GPIO_BASE
    ldr r1, =0x5500
    str r1, [r0, #(PA + PORT_CFG0)]

    ldr r0, =CCU_BASE
    ldr r1, =(1 << 21)
    str r1, [r0, #BUS_CLK_GATING_REG2]
    str r1, [r0, #BUS_SOFT_RST_REG2]

    ldr r0, =UART1_BASE
    ldr r1, =0x00
    str r1, [r0, #UART_IER]
    ldr r1, =0xf7
    str r1, [r0, #UART_IIR]
    ldr r1, =0x00
    str r1, [r0, #UART_MCR]
    ldr r1, [r0, #UART_LCR]
    orr r1, #(1 << 7)
    str r1, [r0, #UART_LCR]
    ldr r1, =54
    str r1, [r0, #UART_DLL]
    ldr r1, =0x00
    str r1, [r0, #UART_DLH]
    ldr r1, [r0, #UART_LCR]
    bic r1, #(1 << 7)
    str r1, [r0, #UART_LCR]
    ldr r1, [r0, #UART_LCR]
    bic r1, #0x1f
    orr r1, #0x03
    str r1, [r0, #UART_LCR]

    ldr r0, =UART1_BASE
    ldr r2, =hello
1:
    ldr r1, [r0, #UART_USR]
    tst r1, #(1 << 1)
    beq 1b
    ldrb r1, [r2]
    strb r1, [r0, #UART_RBR]
    add r2, #1
    cmp r1, #0
    bne 1b

main:
    b main

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

Baudrate 115200bps