Hello, World (bare, no libs yet)

[Scott C. Karlin]

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