S5PV210 serial communication programming practice-2

1. GPIO initialization corresponding to serial port Tx and Rx

Assign corresponding values ​​to the corresponding bits of GPA0CON using C language bit operations.

void uart_init( void )

{

//Initialize the GPIO pins corresponding to Tx and Rx

rGPA0CON &= ~( 0xff << 0 ); // Clear all bits 0 to 7 of the register

rGPA0CON |= 0x00000022; //0b0010, Rx, Tx

}

2. Main control registers such as UCON, ULCON, UMCON, and UFCON

Just set it up according to the values ​​analyzed in the previous section.

void uart_init( void )

{

//Initialize the GPIO pins corresponding to Tx and Rx

rGPA0CON &= ~( 0xff << 0 ); // Clear all bits 0 to 7 of the register

rGPA0CON |= 0x00000022; //0b0010, Rx, Tx

//Settings of several key registers

rULCON0 = 0x3;

rUCON0 = 0x5;

rUMCON0 = 0x0;

rUFCON0 = 0x0;

}

//Baud rate setting DIV_VAL = ( PCLK / (bps x 16) ) - 1 DVI_VAL = (66000000 / (115200 X 16 )) -1 = 34.8 remainder 0.8

//PCLK_PSYS uses 66MHz

//rUBRDIV0 = 34

//rUDIVSLOT0 = 0xdfdd;

//PCLK_PSYS uses 66.7MHz

//DVI_VAL = (66700000 / (115200 X 16 )) -1 = 35.18 remainder 0.18

rUBRDIV0 = 35

//(number of 1s in rUDIVSLOT) / 16 = remainder calculated in the previous step = 0.18

(Number of 1s in rUDIVSLOT) = 16 x 0.18 = 2.88 = 3 (3 1s to find the recommendation table)

rUDIVSLOT0 = 0x0888; //3 1s, look up the table to get this number

3. Calculation and setting of baud rate

(1) The first step is to use PCLK_PSYS and the target baud rate to calculate DIV_VAL = (PCLK / (bps x 16)) - 1

(2) In the second step, the integer part of DIV_VAL is written into the UBRDIV0 register.

(3) In the third step, multiply the decimal part by 16 to get the number of 1s, and then look up the table to get the setting value of the uBDIVSLOT0 register.

4. Writing of serial port sending and receiving functions

//Serial port sending program, send 1 character

void uart_putc( char c )

{

//The serial port sends a character, which actually throws a byte into the send buffer (that is, the UTXH0 register).

rUTXH0 = c;

rUTXH0 = a;

//If you send like the above, the CPU is too fast (because there is no interrupt) and the serial port cannot handle it. At this time, you need to read a status register (UTRSTAT0 register)

//Because the speed at which the serial port controller sends 1 byte is much lower than the speed of the CPU, the CPU must confirm that the current buffer of the serial port controller is empty before sending 1 byte (which means that the serial port has sent the previous byte)

//If the buffer is not empty (UTRSTAT0 register) bit 1 is 0, it should loop until (UTRSTAT0 register) bit 1 is 1.

while( !(rUTRSTAT0 & (1 << 1 ) ) ); //Judge whether the buffer is empty

rUTXH0 = c;

}

(1) Write a sending function. Before sending, use a while loop to wait until the sending buffer is empty.

(2) Serial port receiving program, polling mode, receives one byte

char uart_getc( void )

{

while( !(rUTRSTAT0 & ( 1 << 0 )));

return ( rURXH0 & 0x0f );

}

5. Comprehensive debugging

void main( void )

{

uart_init();

while( 1 ) //keep sending character a

{

uart_putc( 'a' );

delay(); //delay function

{

}

6. Extended Exercise - Debug after changing the baud rate

Check the clock diagram to find the clock source:

Baud rate calculation:

Send and receive status register: