[嵌入式]串口uart编程——基于imx6ull

1.main.c

#include "uart.h"

void delay(volatile int d)
{
	while(d--);
}

int main(void)
{
	char c;
	
	uart_init();
	

	while(1)
	{
		c = getchar();
		putchar(c);
		putchar(c+1);
	}

	return 0;
}

2.uart.c

/*
	设置uart的总时钟寄存器：CCM_CSCDR1；地址：20C_4024h；设置的位bit0-5：000000；bit6：0（80m）

	给uart1提供时钟寄存器：CCM_CCGR5；地址：20C_407Ch；设置的位：24-25：设置为11

	配置引脚功能寄存器：SW_MUX_CTL_PAD_UART1_TX_DATA；地址：20E_0084h；设置的位：0-3：设置为0000
						SW_MUX_CTL_PAD_UART1_RX_DATA；地址：20E_0088h；设置的位：0-3：设置为0000

	imx6ull中对uart的特殊要求寄存器：UART1_RX_DATA_SELECT_INPUT；地址：20E_0624h；设置的位：bit0-1:设置为11

	设置波特率寄存器：UARTx_UBIR和UARTx_UBMR；地址：202_00A4和202_00A8；

	设置数据格式寄存器：UART1_UCR2；地址：202_0084

	imx6ull芯片要求必须设置寄存器：UART1_UCR3；地址：202_0088；设置的位：bit2必须是1（很奇怪，既然必须是1，那为什么不直接定死）

	使能uart1寄存器：UARTx_UCR1；地址：201_8080；设置的位：bit0：设置为1	
*/

#include "uart.h"

/*根据IMX6ULL芯片手册<<55.15 UART Memory Map/Register Definition>>的3608页，定义UART的结构体,*/
typedef struct {
  volatile unsigned int  URXD;               /**< UART Receiver Register, offset: 0x0 	           串口接收寄存器，偏移地址0x0     */
  		   unsigned char RESERVED_0[60];		
  volatile unsigned int  UTXD;               /**< UART Transmitter Register, offset: 0x40          串口发送寄存器，偏移地址0x40*/
  		   unsigned char RESERVED_1[60];		
  volatile unsigned int  UCR1;               /**< UART Control Register 1, offset: 0x80 	       串口控制寄存器1，偏移地址0x80*/
  volatile unsigned int  UCR2;               /**< UART Control Register 2, offset: 0x84 	       串口控制寄存器2，偏移地址0x84*/
  volatile unsigned int  UCR3;               /**< UART Control Register 3, offset: 0x88            串口控制寄存器3，偏移地址0x88*/
  volatile unsigned int  UCR4;               /**< UART Control Register 4, offset: 0x8C            串口控制寄存器4，偏移地址0x8C*/
  volatile unsigned int  UFCR;               /**< UART FIFO Control Register, offset: 0x90         串口FIFO控制寄存器，偏移地址0x90*/
  volatile unsigned int  USR1;               /**< UART Status Register 1, offset: 0x94             串口状态寄存器1，偏移地址0x94*/
volatile unsigned int  USR2;               /**< UART Status Register 2, offset: 0x98             串口状态寄存器2，偏移地址0x98*/
  volatile unsigned int  UESC;               /**< UART Escape Character Register, offset: 0x9C     串口转义字符寄存器，偏移地址0x9C*/
  volatile unsigned int  UTIM;               /**< UART Escape Timer Register, offset: 0xA0         串口转义定时器寄存器 偏移地址0xA0*/
  volatile unsigned int  UBIR;               /**< UART BRM Incremental Register, offset: 0xA4      串口二进制倍率增加寄存器 偏移地址0xA4*/
  volatile unsigned int  UBMR;               /**< UART BRM Modulator Register, offset: 0xA8 	   串口二进制倍率调节寄存器 偏移地址0xA8*/
  volatile unsigned int  UBRC;               /**< UART Baud Rate Count Register, offset: 0xAC      串口波特率计数寄存器 偏移地址0xAC*/
  volatile unsigned int  ONEMS;              /**< UART One Millisecond Register, offset: 0xB0      串口一毫秒寄存器 偏移地址0xB0*/
  volatile unsigned int  UTS;                /**< UART Test Register, offset: 0xB4                 串口测试寄存器 偏移地址0xB4*/		
  volatile unsigned int  UMCR;               /**< UART RS-485 Mode Control Register, offset: 0xB8  串口485模式控制寄存器 偏移地址0xB8*/
} UART_Type;


void uart_init(void)
{
	volatile unsigned int *IOMUXC_SW_MUX_CTL_PAD_UART1_TX_DATA ;
	volatile unsigned int *IOMUXC_SW_MUX_CTL_PAD_UART1_RX_DATA	;
	volatile unsigned int *IOMUXC_UART1_RX_DATA_SELECT_INPUT ;
	volatile unsigned int *CCM_CSCDR1;
	volatile unsigned int *CCM_CCGR5;

	UART_Type *uart1 = (UART_Type *)0x02020000;

	IOMUXC_SW_MUX_CTL_PAD_UART1_TX_DATA		= (volatile unsigned int *)(0x20E0084);
	IOMUXC_SW_MUX_CTL_PAD_UART1_RX_DATA		= (volatile unsigned int *)(0x20E0088);
	IOMUXC_UART1_RX_DATA_SELECT_INPUT		= (volatile unsigned int *)(0x20E0624);
	CCM_CSCDR1 = (volatile unsigned int *)(0x020C4024);
	CCM_CCGR5 = (volatile unsigned int *)(0x020C407C);

	/* 设置uart的总时钟 
		UART_CLK_PODF = 80MHZ
	*/
	*CCM_CSCDR1 &= ~((1<<6) | (0x3f));

	/* 给uart1提供时钟 
		uart1_clk_enable
	*/
	*CCM_CCGR5 |= (3<<24);

	/* 配置引脚功能寄存器 */
	*IOMUXC_SW_MUX_CTL_PAD_UART1_TX_DATA &= ~0xf;
	*IOMUXC_SW_MUX_CTL_PAD_UART1_RX_DATA &= ~0xf;

	/* imx6ull中对uart的特殊要求 */
	*IOMUXC_UART1_RX_DATA_SELECT_INPUT |= 3; 

	/* 设置波特率
		115200 = 80M/(16 * (UBMR+1)/(UBIR+1))
		为了方便运算，干脆让UBIR = 15，消掉16
		所以115200 = 80M/(UBMR+1)
		UBMR = 80000000 / 115200 = 694 -1 = 693
?		真正的baudrate = 80000000 / 694 = 115274  ?为啥不是80m的单位不转化为bit	
		先设置UBIR，在设置UBMR
	*/
	uart1->UFCR |= (5<<7); 
	uart1->UBIR = 15;
	uart1->UBMR = 693;

	/* 设置数据格式 */
	uart1->UCR2 |= (1<<14) | (0<<8) | (0<<6) | (1<<5) | (1<<2) | (1<<1);

	/* imx6ull芯片规定的必须设置的 */
	uart1->UCR3 |= (1<<2);

	/* 使能uart1 */
	uart1->UCR1 |= (1<<0);
}

int getchar(void)
{
	UART_Type *uart1 = (UART_Type *)0x02020000;

	while((uart1->USR2 & (1<<0)) == 0);

	return uart1->URXD;
}

char putchar(char c)
{
	UART_Type *uart1 = (UART_Type *)0x02020000;
	
	while((uart1->USR2 & (1<<3)) == 0);
	
	uart1->UTXD = c;

	return c;
}

3.uart.h

/* 有些文件可能会多次包含这个.h文件，包含一次就声明一次，为了避免多次声明 */
#ifndef _UART_H
#define _UART_H
void uart_init(void);
int getchar(void);
char putchar(char c);
#endif

3.Makefile

PREFIX=arm-linux-gnueabihf-
CC=$(PREFIX)gcc
LD=$(PREFIX)ld
AR=$(PREFIX)ar
OBJCOPY=$(PREFIX)objcopy
OBJDUMP=$(PREFIX)objdump

led.img : start.S uart.c main.c
	$(CC) -nostdlib -g -c -o start.o start.S
	$(CC) -nostdlib -g -c -o uart.o uart.c	
	$(CC) -nostdlib -g -c -o main.o main.c	
	
	$(LD) -T imx6ull.lds -g start.o uart.o main.o -o led.elf 
	
	$(OBJCOPY) -O binary -S led.elf  led.bin
	$(OBJDUMP) -D -m arm  led.elf  > led.dis	
	mkimage -n ./tools/imximage.cfg.cfgtmp -T imximage -e 0x80100000 -d led.bin led.imx
	dd if=/dev/zero of=1k.bin bs=1024 count=1
	cat 1k.bin led.imx > led.img

clean:
	rm -f led.dis  led.bin led.elf led.imx led.img *.o

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