This has worked for me using the standard bcm2709.uart_clock=3000000 clock setting in cmdline.txt with the ttyAMA0 default removed.
It uses mmap to directly set the PL011 registers according to the ARM datasheet.
The datasheet can be found here.
http://infocenter.arm.com/help/topic/co ... p5_trm.pdf
Sections 3.3.5 & 3.3.6 cover the baud rate registers, including the calculation.
I have cut it from a class, so it may want a few more basic includes adding.
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#include <termios.h>
#include <sys/mman.h>
#include <errno.h>
//#define UART_BASE 0x20201000 // PL011 USART -->B+
#define UART_BASE 0x3F201000 // PL011 USART (PI2B+)
int fd = 0;
int mem_fd = 0;
int errsv = 0;
volatile unsigned* uart = NULL;
void* uart_map = NULL;
void* IBRD = NULL;
void* FBRD = NULL;
void* LCRH = NULL;
void* UARTCR = NULL;
void* UARTFR = NULL;
uint32_t brd = 0;
struct termios termios_s; // save for restore
struct termios termios_p;
fd = open( "/dev/ttyAMA0", O_RDWR | O_NOCTTY | O_NONBLOCK );
if( fd > 0 ) // set the configuration for the terminal
{
tcgetattr( fd, &termios_s );
cfmakeraw( &termios_p );
termios_p.c_lflag &= ~ISIG; // no signals
termios_p.c_lflag &= ~ICANON; // no canonical mode
termios_p.c_lflag &= ~ECHO; // no echo input
termios_p.c_lflag &= ~NOFLSH; // no flushing on SIGINT
termios_p.c_lflag &= ~IEXTEN; // no input processing
termios_p.c_cc[VMIN] = 0;
termios_p.c_cc[VTIME] = 0;
tcsetattr( fd, TCSADRAIN, &termios_p );
// enable the mmap
if( ( mem_fd = open( "/dev/mem", O_RDWR | O_SYNC ) ) < 0 )
{
fprintf( stdout, "can't open /dev/mem for mmap(). Did you use 'sudo' ?\n" );
return;
}
uart_map = mmap( NULL, BLOCK_SIZE, PROT_READ | PROT_WRITE, MAP_SHARED, mem_fd, UART_BASE );
close( mem_fd );
if( uart_map == MAP_FAILED )
{
errsv = errno;
fprintf( stdout,"uart mmap failed\n" );
fprintf( stdout, "error %d %s\n", errsv, strerror( errsv ) );
}
else
{
uart = (volatile unsigned*)uart_map;
UARTFR = (void*)( (uint32_t)uart + 0x18 );
IBRD = (void*)( (uint32_t)uart + 0x24 );
FBRD = (void*)( (uint32_t)uart + 0x28 );
LCRH = (void*)( (uint32_t)uart + 0x2C );
UARTCR = (void*)( (uint32_t)uart + 0x30 );
// first, disable the uart and flush the fifos
brd = 0x00;
memcpy( UARTCR, &brd, 4 );
// check for completion of any tx/rx
memcpy( &brd, UARTFR, 4 );
while( brd & 0x08 )
{
usleep( 1 ); // wait a bit
memcpy( &brd, UARTFR, 4 );
}
brd = 6; // 3000000 / ( 16 * 31250 ) = 6.0
memcpy( IBRD, &brd, 4 );
brd = 0;
memcpy( FBRD, &brd, 4 );
brd = 0x70; // 8 bit data, FIFO enabled
memcpy( LCRH, &brd, 4 );
// enable uart, tex, rex etc.
brd = 0x0301;
memcpy( UARTCR, &brd, 4 );
}
}
else
{
errsv = errno;
fprintf( stdout,"/dev/ttyAMA0 access failed\n" );
fprintf( stdout, "error %d %s\n", errsv, strerror( errsv ) );
fd = 0;
}
Then use read and write using fd as the file.
e.g. to read to a buffer called 'data'
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int32_t i = 0;
i = read( fd, data, 128 );
if( i == -1 )
{
errsv = errno;
fprintf( stdout, "serial failed read\n" );
fprintf( stdout, "error %d %s\n", errsv, strerror( errsv ) );
}
'i' will contain the number of bytes read.
Don't forget to tidy up once you have finished.
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if( uart_map ) munmap( uart_map, BLOCK_SIZE ); // close mmap
if( fd )
{
tcsetattr( fd, TCSANOW, &termios_s ); // restore saved settings
close( fd );
}
...
.