ARM Notes: UART Program

UART program:
1. The writing function of head.S file is to start the code

@******************************************************************************

@ File：head.S

@ Function: Initialization, system mode stack

@******************************************************************************       

.extern     main

.text 

.global _start 

_start:

    b   Reset

Reset:                  

    ldr sp, =4096 @ Set the stack pointer. The following are all C functions. You need to set the stack before calling them.

    bl disable_watch_dog @ Disable WATCHDOG, otherwise the CPU will restart continuously

    bl clock_init @ Set up MPLL, change FCLK, HCLK, PCLK

    bl memsetup @ Set up the memory controller to use SDRAM

   bl inituart@ written inituart() serial port initialization function in init.c

    bl copy_steppingstone_to_sdram @ Copy code to SDRAM

    ldr pc, =on_sdram @ Jump to SDRAM and continue execution

on_sdram:

    msr cpsr_c, #0xdf @ Enter system mode

    ldr sp, =0x34000000 @ Set the system mode stack pointer,

    ldr lr, =halt_loop @ Set the return address

    ldr pc, =Main @ Call the main function

halt_loop:

    b   halt_loop

2. init.c file, which declares some functions and implementations that need to be used 

#include "2440addr.h"

void disable_watch_dog(void);

void clock_init(void);

void memsetup(void);

void copy_steppingstone_to_sdram(void);

void inituart(void);

void disable_watch_dog(void)

{

    rWTCON = 0; // Turning off WATCHDOG is very simple, just write 0 to this register

}

#define S3C2410_MPLL_200MHZ     ((0x5c<<12)|(0x04<<4)|(0x00))

#define S3C2440_MPLL_200MHZ     ((0x5c<<12)|(0x01<<4)|(0x02))

void clock_init(void)

{

    // LOCKTIME = 0x00ffffff; // Use the default value

    rCLKDIVN  = 0x03;            // FCLK:HCLK:PCLK=1:2:4, HDIVN=1,PDIVN=1

__asm__(

    "mrc    p15, 0, r1, c1, c0, 0\n"         

    "orr    r1, r1, #0xc0000000\n"          

    "mcr    p15, 0, r1, c1, c0, 0\n"        

    );

    if ((rGSTATUS1 == 0x32410000) || (rGSTATUS1 == 0x32410002))

    {

        rMPLLCON = S3C2410_MPLL_200MHZ;  

    }

    else

    {

        rMPLLCON = S3C2440_MPLL_200MHZ;  

    }       

}

void memsetup(void)

{

    volatile unsigned long *p = (volatile unsigned long *)MEM_CTL_BASE;

    p[0] = 0x22011110;     //BWSCON

    p[1] = 0x00000700; //BANKCON0

    p[2] = 0x00000700; //BANKCON1

    p[3] = 0x00000700; //BANKCON2

    p[4] = 0x00000700; //BANKCON3  

    p[5] = 0x00000700; //BANKCON4

    p[6] = 0x00000700; //BANKCON5

    p[7] = 0x00018005;     //BANKCON6

    p[8] = 0x00018005;     //BANKCON7

    p[9]  = 0x008C04F4;

    p[10] = 0x000000B1;     //BANKSIZE

    p[11] = 0x00000030;     //MRSRB6

    p[12] = 0x00000030;     //MRSRB7

}

void copy_steppingstone_to_sdram(void)

{

    unsigned int *pdwSrc  = (unsigned int *)0;

    unsigned int *pdwDest = (unsigned int *)0x30000000;

    while (pdwSrc < (unsigned int *)4096)

    {

        *pdwDest = *pdwSrc;

        pdwDest++;

        pdwSrc++;

    }

}

void inituart(void)

{

rGPBCON = 0x015551;

rGPBUP  = 0x7ff;

rGPBDAT = 0x1e0;

rGPHCON = 0x00faaa; //Use UART0 function

rGPHUP  = 0x7ff;

rULCON0 = 0x3; //Set UART0 to no parity, one stop bit, 8 data bits

rUCON0 = 0x245; //PCLK is the clock source, receiving and sending data is in query or interrupt mode

rUFCON0 = 0;                     //

rUMCON0 = 0; //

rUBRDIV0 = 26;  

}

3. uart.c This program uses the query method to implement serial communication

#include"2440addr.h"

void Main(void)

{

       char ch;

               //Set the baud rate, PCLK is 50MHz, and the baud rate is 115.2kHz

while(!(rUTRSTAT0 & 0x2)); //Wait and determine whether the send buffer is empty

       rUTXH0 = 0xaa; //If it is empty, send 0xAA byte

while(1)

{

              while(!(rUTRSTAT0 & 0x1)); //Wait and determine whether the receive buffer is ready

 ch = rURXH0; //Receive one byte of data

              while(!(rUTRSTAT0 & 0x2)); //Wait and determine whether the send buffer is empty

              rUTXH0 = ch; //Send one byte of data

switch(ch) //Execute different programs according to the received data

              {

       case 0x11: // Turn off LED

                           rGPBDAT |= 0x1e0;

       break;

                                 case 0x22: //light up the LED

                             rGPBDAT &= 0x1f;

                     break;

       case 0x33: //Buzzer does not sound

                               rGPBDAT &= 0x1e0;

                           break;

                                case 0x44: //Buzzer sounds

                                     rGPBDAT |= 0x1;

                                     break;

                                default: //LED off, buzzer off

                                     rGPBDAT = 0x1e0;

                                     break;

}

}

}

4. The specific function of the uart.lds file is not very clear. I personally feel that it should be used for segment declarations and entry addresses.

SECTIONS {

    . = 0x30000000;

    .text          :   { *(.text) }

    .rodata ALIGN(4) : {*(.rodata)} 

    .data ALIGN(4) : { *(.data) }

    .bss ALIGN(4)  : { *(.bss)  *(COMMON) }

}

5. Makefile 

objs := head.o uart.o init.o

uart.bin: $(objs)

arm-linux-ld -Tuart.lds -o uart_elf $^

arm-linux-objcopy -O binary -S uart_elf $@

arm-linux-objdump -D -m arm uart_elf > uart.dis

%.o:%.c

arm-linux-gcc -Wall -O2 -c -o $@ $<