Question

I would like to use printf to diplay text on a serial port of an ARM microcontroller. I am unable to do so. Any help is appreciated.

My init_serial looks like this

void init_serial (void)
{
PINSEL0 = 0x00050000; /* Enable RXD1 TxD1 */
U1LCR = 0x00000083; /*8 bits, 1 Stop bit */
U1DLL = 0x000000C2; /*9600 Baud Rate @12MHz VPB Clock */
U1LCR = 0x00000003; /* DLAB=0*/
}

which is obviously wrong.

Answer 1

For microcontollers, you typically have to define your own putc function to send bytes to whichever UART you’re using. print will then call your putc.

Check the documentation for the libraries supplied with your compiler.

Note that this is entirely unrelated to how you intialise your UART. All that matters is which UART you’re using.

(On an unrelated issue, rather than saying:

PINSEL0 = 0x00050000; /* Enable RXD1 TxD1 */
U1LCR   = 0x00000083; /*8 bits, 1 Stop bit */

there are typically #defines for registers which (usually) aid readability, provide a link to the bit names in the documentation, and reduce the need for comments to be added and maintained on every line like these. For example:

PINSEL0 = PICSEL0_RXD1EN | PICSEL0_TXD1EN;
U1LCR   = U1LCR_8BITS | U1LCR_1STOPBIT;

..and so on.)