15.uboot study serial port initialization

About the serial

For developers of embedded devices, the beginning of a lot of equipment are not available, unable to get the program running, the debugger takes a lot of time and effort, so the role of the serial port for debugging embedded programs is obvious, when the serial port can not be used, may only a slight indication of the program running with the light off to led after with serial port, you can get more debugging information. S3C6410 serial port and other equipment used are similar, the initial configuration after the serial port can send and receive the data. First, look at the serial block diagram of the chip Manual:

uart
serial transmission data signal lines, the TXDn signal lines, data signal lines receiving RXDn, as shown above, these two signal lines are connected to the transmit shift register and a receive shift register, serial addition further comprising a FIFO module is used to send and receive data 64Bytes two. In addition to a control unit in addition to generating module and the baud rate, corresponding parts are connected to the upper peripheral bus system.

Serial register

First look at the relevant register:
uart1
S3C6410 has UART0,1,2,3 four serial ports, above only lists the relevant register in serial-0, several other serial register descriptions and this, like, let's say in detail below:

###### ULCONx: serial data formatting data length, the stop bit length, parity bits
ulcon

UCONx: serial control clock source selection register, transmit and receive mode

ucon
ucon

UFCONx: FIFO Control Register Set Enable FIFO trigger level

ufcon

UTRSTATx: transmitting and receiving status register

utrstat

UERSTATx: frame error status register error, parity errors

uerstat

UFSTATx: FIFO Status Register

UFSTAT

UTXx: transmit data register data to be transmitted it threw

utx

URXx: receiving data register to obtain the data received from the register

urx

UBRDIV: baud rate divisor value register

ubrdiv

UDIVSLOT: baud rate divisor value fractional part (I'm from the name ...)

slot

Serial port initialization

Serial port initialization tasks to be done mainly in the following:

Configuring GPIO pin function is related to the serial port functions
Provided ULCONx serial data format to set the register, the data bit length, stop bit length, parity bits, etc.
Set the serial port control register UCONx, serial clock source select, send and receive data modes: an interrupt, polling, interrupts the DMA
Set the baud rate frequency division number register and fractional part of the division value of the baud rate register
FIFO control register set, whether the FIFO is enabled and the like

###### baud rate is set
BAUD
baud rate divisor value:
DIV_VAL = (the PCLK / (bps 16)) -. 1
EG:
the PCLK = 66.5M = 66.5 million
bps baud rate = 115200
DIV_VAL = (66500000/115200 16) -1 = 35.078
UBRDIVn = 35
fractional part of 0.078
UDIVSLOTn 1 divided by the number of = 0.078 16
UDIVSLOTn the number of 1s = 1 = 1.248
according to the table, so that a value of 0x0080 UDIVSLOTn;

Code


#define UCON0      (*((volatile unsigned long *)0x7F005004))
#define UFCON0     (*((volatile unsigned long *)0x7F005008))
#define UMCON0     (*((volatile unsigned long *)0x7F00500C))
#define UTRSTAT0   (*((volatile unsigned long *)0x7F005010))
#define UFSTAT0    (*((volatile unsigned long *)0x7F005018))
#define UTXH0      (*((volatile unsigned char *)0x7F005020))
#大专栏  15.uboot study 串口初始化eta-keyword">define URXH0      (*((volatile unsigned char *)0x7F005024))
#define UBRDIV0    (*((volatile unsigned short *)0x7F005028))
#define UDIVSLOT0  (*((volatile unsigned short *)0x7F00502C))
#define GPACON     (*((volatile unsigned long *)0x7F008000))
#define PCLK 66500000
#define BOUD 115200

void uart_init(void)
{
    GPACON &= ~0xff;
    GPACON |= 0x22;

    
    ULCON0 = 0x3;  /* 数据位:8, 无较验, 停止位: 1, 8n1 */
    UCON0  = 0x5;  /* 使能UART发送、接收 */
    UFCON0 = 0x01; /* FIFO ENABLE */

    UMCON0 = 0;

    /* 波特率 */
    /* DIV_VAL = (PCLK / (bps x 16 ) ) - 1 
     * bps = 115200
     * DIV_VAL = (66000000 / (115200 x 16 ) ) - 1 
     *         = 35.08
     */
    UBRDIV0 = (int)(PCLK/(BOUD*16)-1);

    /* x/16 = 0.08
     * x = 1
     */
    UDIVSLOT0 = 0x1;

}

void putc(unsigned char c)
{
    while (UFSTAT0 & (1<<14)); /* 如果TX FIFO满，等待 */
    UTXH0 = c;                         /* 写数据 */
}


unsigned char getc(void)
{
    unsigned char ret;
    while ((UFSTAT0 & 0x7f) == 0);  /* 如果RX FIFO空，等待 */
    ret = URXH0;                   /* 取数据 */
    if((ret == 0x0d) || (ret == 0x0a))
    {
        putc(0x0d);
        putc(0x0a);
    }
    else
    {
        putc(ret);
    }

        return ret;
}


void uart_send_string(char *str)
{
    while(*str)
    {
        putc(*str++);    
    }
    putc(0x0d);
    putc(0x0a);    
}

Reprint please indicate the original content Chai Kun-yan and the source http://ykzhai.top/2016/08/15/ Development / Embedded / s3c6410 / 15-uboot-study- serial port initialization /

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