Hello, World (bare, no libs yet)

9 May 2000

      Just an update to my previous post about building StrongARM
tools under linux...

As it turns out the "mysterious" file format the vxWorks boot
loader expects is simply "coff-arm-little."

After rebuilding the tools, I now have a "Hello, World" program
which sends characters out the serial port.  It does not use any
library calls (e.g., printf).

I am now in the process of getting the standard runtime
libraries working.  This way, I can use printf().  I'll let
everyone know when this is working.

In the meantime, in case anyone is interested, here's
what I did to get it working:

1.  Build the tools for arm-unknown-coff.
    I followed the steps in the CrossGCC FAQ online at
    http://www.objsw.com/CrossGCC/ and used GCC 2.95.2,
    binutils 2.9.1, and newlib 1.8.2.  Before building the
    tools, I edited newlib-1.8.2/newlib/configure.host by
    commenting out both ARM_RDP_MONITOR and ARM_RDI_MONITOR.

2.  Here is the program:

*************************************************************************/
/*
**  UART Definitions
*/
#define UART_SR  0x90003400    /* UART Status Register Address      */
#define TXF      0x00000080    /*    Transmit FIFO full bit         */
#define RXR      0x00000010    /*    Receive FIFO ready (not empty) */

#define UART_CR  0x90003800    /* UART Control Register Address     */
#define XIE      0x00000100    /*    Transmit interrupt enable bit  */
#define RIE      0x00000010    /*    Receive interrupt enable bit   */

#define UART_DR  0x90003C00    /* UART Data Register Address        */

/*
**  Forward References
*/
static void noUartInts(void);
static void putchar(int c);
static void puts(char *s);
static int getchar(void);

/*
**  Entry Point
*/
void __main(void)
{
   int c;

   noUartInts();

   puts("Hello, World!\n\r");

   puts("\n\r");

   puts("Enter characters to be echoed:\n\r");

   while(1)
      {
         c = getchar();
         if(c == '\r')
            {
               puts("\n\r");
            }
         else
            {
               putchar(c);
            }
      }
}

/*
**  Disable UART transmit/receive interrupts
*/
static void noUartInts(void)
{
   volatile unsigned long *ptrCR;

   ptrCR = (volatile unsigned long *) UART_CR;

   *ptrCR &= ~(XIE | RIE);
}

/*
**  Send a single character
*/
static void putchar(int c)
{
   volatile unsigned long *ptrSR;
   volatile unsigned long *ptrDR;

   ptrSR = (volatile unsigned long *) UART_SR;

   while((*ptrSR & TXF) != 0)
      ;

   ptrDR = (volatile unsigned long *) UART_DR;

   *ptrDR = (unsigned long) c;
}

/*
**  Send a null terminated string
*/
static void puts(char *s)
{
   int c;

   while((c = *s++) != '\0')
      {
         putchar(c);
      }
}
/*
**  Get a character
*/
static int getchar(void)
{
   volatile unsigned long *ptrSR;
   volatile unsigned long *ptrDR;

   ptrSR = (volatile unsigned long *) UART_SR;

   while((*ptrSR & RXR) == 0)
      ;

   ptrDR = (volatile unsigned long *) UART_DR;

   return (int) *ptrDR;
}

/*************************************************************************/

3.  Here are the commands I used to compile the code:

       arm-unknown-coff-gcc -I. -nostartfiles -nodefaultlibs \
       -fno-builtin -mcpu=strongarm110 -mapcs-32 -mno-sched-prolog \
       -fvolatile -Wall -Wstrict-prototypes -O2 -c hw.c -o hw.o

       arm-unknown-coff-ld -o hw.coff hw.o -X -N -e ___main \
       -Ttext 00001000

-Scott

Hello, World (bare, no libs yet)

Scott C. Karlin