/* 手冊定好的計算方式，不需要問為什么，直接套公式即可。DIV_VAL = (40000000/(115200 x 16))  –  1= 21.7 – 1= 20.7UBRDIVn = 20 (integer part of DIV_VAL)UFRACVALn/16 = 0.7 So, UFRACVALn = 11*/50000000 / (115200 * 16) - 1 = 27.13 - 1 = 26.13 = 26 【==UBRDIV0】0.13 * 16 = 2.08 = 2 【==UFRACVAL0】【匯總】S5P6818UART相關寄存器1) UART行控制器ULCONn - 設置數據格式2) UART模式控制寄存器UCONn - 用來選擇時鐘源，發送/接收數據可選輪詢3) UART FIFO控制寄存器UFCONn4) UART MODEM控制寄存器UMCONn5) 發送寄存器UTXH、接收寄存器URXH6) 波特率分頻寄存器UBRDIV，UFRACVAL7) GPIO相關寄存器8) 中斷相關寄存器9) 時鐘、電源控制寄存器4. 編碼
/** 代碼演示 - main.c **/#include "uart.h"void main (void) {    // 8N1 115200 non-FIFO polling    uart_init ( );    while (1) {        uart_puts ("/n hello,world!");    }   }
/** 代碼演示 - uart.c **/#define UART0CLKENB     *((volatile unsigned int*)0xc00a9000)#define UART0CLKGEN0L   *((volatile unsigned int*)0xc00a9004)#define GPIOD_ALTFN0    *((volatile unsigned int*)0xc001d020)#define GPIOD_ALTFN1    *((volatile unsigned int*)0xc001d024)#define GPIOD_PULLENB   *((volatile unsigned int*)0xc001d060)#define ULCON0          *((volatile unsigned int*)0xc00a1000)#define UCON0           *((volatile unsigned int*)0xc00a1004)#define UFCON0          *((volatile unsigned int*)0xc00a1008)#define UTRSTAT0        *((volatile unsigned int*)0xc00a1010)#define UTXH0           *((volatile unsigned int*)0xc00a1020)#define URXH0           *((volatile unsigned int*)0xc00a1024)#define UBRDIV0         *((volatile unsigned int*)0xc00a1028)#define UFRACVAL0       *((volatile unsigned int*)0xc00a102c)void uart_init (void) {    /* uart0 clk disable */    UART0CLKENB &= ~(1 << 2);    // GPIOD18(Tx 接收管腳) GPIOD14(Rx 發送管腳) 配置功能Function1    GPIOD_ALTFN0 &= ~(3 << 28); // GPIOD14    GPIOD_ALTFN0 |= (1 << 28);    GPIOD_ALTFN1 &= ~(3 << 4); // GPIOD18    GPIOD_ALTFN1 |= (1 << 4);    // 時鐘配置：選擇PLL[1] 800MHz    UART0CLKGEN0L &= ~(7 << 2);    UART0CLKGEN0L |= (1 << 2);    // 分頻設置 800/(0x0f+1)=50MHz    UART0CLKGEN0L &= ~(0xff << 5); // [12:5] 8個位    UART0CLKGEN0L |= (0xf << 5); // [12:5] 4個位設置為1111    // UART控制器設置    ULCON0  = 0x03; // 8N1    UCON0   = 0x05; // 0101 == 0x05 polling    UFCON0 &= ~(1 << 0); // non-FIFO disable    UBRDIV0 = 26; // 50000000/(115200*16) - 1 == 26.13    UFRACVAL0 = 2; // 0.13*16 == 2.08    /* uart0 clk enable */    UART0CLKENB |= (1 << 2);}void uart_putc (char c) {    // UTRSTAT0 bit[1] == 1, 緩存寄存器為empty    // 輪詢是否為空    while (! (UTRSTAT0 & 0x02)); // !(空) 什么都不干。    UTXH0 = c;    if (c == '/n')        uart_putc ('/r');}void uart_puts (char* str) {    if (! str)        return ;    while (*str) {        uart_putc (*str);        str++;    }}
/** 代碼演示 - uart.h **/#ifndef _UART_H_#define _UART_H_extern void uart_init (void);extern void uart_puts (char*);#endif //_UART_H_
5. 編譯
$:' arm-cortex_a9-linux-gnueabi-gcc -c -nostdlib main.c -o main.o$:' arm-cortex_a9-linux-gnueabi-gcc -c -nostdlib uart.c -o uart.o$:' arm-cortex_a9-linux-gnueabi-ld -nostdlib -nostartfiles -Ttext=48000000 -emain main.o uart.o -o uart      // 注意.o文件順序$:' arm-cortex_a9-linux-gnueabi-objcopy -O binary uart uart.bin6. 運行$:' sudo cp uart.bin /tftpboot/X6818#:' tftp 48000000 uart.binX6818#:' go 48000000