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@SlightlyLoony SlightlyLoony/port.c
Last active Feb 26, 2019

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Raspbian program to set U-Blox GPS to stationary mode, and save configuration
#include <stdio.h>
#include <unistd.h>
#include <fcntl.h>
#include <termios.h>
/*
Simple program that sets stationary mode in U-Blox GPS connected to serial 0 on a Raspberry Pi 3 running Jessie. This
was not tested on any other system. This program assumes the GPS is using its default 9600 baud, 8 data bits, 1 stop bit,
and no parity. I'm using the expansion board from Uputronics.
This program worked for me when I set up my Pi as a stratum 1 NTP server per the directions on this
web page: https://ava.upuaut.net/?p=726&cpage=1
Initially I had problems with the code that page points to in a section titled "Setting Stationary Mode". That program
compiled just fine, but simply hung on the call to open(). As I started to troubleshoot that code, I realized it had more
problems than just the hanging, so I wrote this.
My apologies in advance for the lack of generalization and the generally bad code. My only excuse is that this is the first
C program I've written in about 30 years (I've been working in Java for 20 years, and C++ before that)...
*/
struct ubxMsg {
int size;
unsigned char* msg;
};
unsigned char stationary[] = {
0xB5, 0x62, /* message header */ \
0x06, 0x24, /* message class and ID */ \
0x24, 0x00, /* message body length */ \
0xFF, 0xFF, /* parameters bitmask */ \
0x02, /* dynamic platform model: stationary */ \
0x03, /* position fixing mode: auto 2D/3D */ \
0x00, 0x00, 0x00, 0x00, /* fixed altitude for 2D fix mode: 0 m */ \
0x10, 0x27, 0x00, 0x00, /* fixed altitude variance for 2D fix mode: 1 m^2 */ \
0x05, /* minimum elevation for GNSS satellite: 5 degrees */ \
0x00, /* reserved */ \
0xFA, 0x00, /* position DOP mask: 0x00FA */ \
0xFA, 0x00, /* time DOP mask: 0x00FA */ \
0x64, 0x00, /* position accuracy mask: 100 m */ \
0x2C, 0x01, /* time accuracy mask: 300 m */ \
0x00, /* static hold threshold: 0 cm/s */ \
0x3C, /* DGNSS timeout: 60 seconds */ \
0x00, /* number of satellites required above C/N0 threshold */ \
0x00, /* C/N0 threshold: 0dBHz */ \
0x00, 0x00, /* reserved */ \
0x00, 0x00, /* static hold distance threshold: 0 m */ \
0x00, /* UTC standard: auto */ \
0x00, 0x00, 0x00, 0x00, /* reserved */ \
0x00, /* reserved */ \
0x4E, 0x60 /* checksum */ \
};
unsigned char save[] = {0xB5, 0x62, 0x06, 0x09, 0x0D, 0x00, 0x00, 0x00, 0x00, 0x00, 0xFF, 0xFF, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x03, 0x1D, 0xAB};
struct ubxMsg getStationaryMessage() {
struct ubxMsg result;
result.msg = stationary;
result.size = sizeof( stationary );
return result;
}
struct ubxMsg getSaveConfigurationMessage() {
struct ubxMsg result;
result.msg = save;
result.size = sizeof( save );
return result;
}
int openUART() {
int fd = -1;
fd = open("/dev/serial0", O_RDWR | O_NOCTTY | O_NDELAY); //Open in non blocking read/write mode
if (fd == -1)
{
printf( "Can't open serial0 - possibly it's in use by another application\n" );
}
struct termios options;
tcgetattr(fd, &options);
options.c_cflag = B9600 | CS8 | CLOCAL | CREAD;
options.c_iflag = IGNPAR;
options.c_oflag = 0;
options.c_lflag = 0;
tcflush(fd, TCIFLUSH);
tcsetattr(fd, TCSANOW, &options);
return fd;
}
// returns character if available, otherwise -1
int readUART( int fd ) {
// Read a character from the port, if there is one
unsigned char rx_buffer[1];
int rx_length = read( fd, (void*)rx_buffer, 1 ); //Filestream, buffer to store in, number of bytes to read (max)
if (rx_length < 0)
{
if( rx_length < -1 ) {
printf( "Read error, %d\n", rx_length );
return -2;
}
return -1;
}
else if (rx_length == 0)
{
//No data waiting
return -1;
}
else
{
//Bytes received
return rx_buffer[0];
}
}
// waits up to five seconds for the given string to be read
// returns 0 for failure, 1 for success
int waitForString( int fd, char* str, int size ) {
int attempts = 0;
int gotIt = 0;
int index = 0;
while( (attempts < 5000) && (gotIt == 0) ) {
usleep( 1000 );
int x = readUART( fd );
if( x >= 0 ) {
//printf("%c", x);
if( x == str[index] ) {
index++;
if( index == size ) {
gotIt = 1;
}
}
else {
index = 0;
}
}
attempts++;
}
return gotIt;
}
// return 0 if error, 1 if succeeded
int sendUBXMessage( int fd, struct ubxMsg msg ) {
// first we wait until our receiver is synchronized, by looking for a message
// we know should be happening often ("$GNGGA,")
// we'll wait up to five seconds for this
if( waitForString( fd, "$GNGGA,", 7 ) == 0 )
return 0;
printf( "Synchronized...\n" );
// then we blast the message out...
//printf("message size: %d\n", msg.size);
int c = write( fd, msg.msg, msg.size );
// construct our expected acknowledge message and wait for it
unsigned char expect[] = {0xb5, 0x62, 0x05, 0x01, 0x02, 0x00, 0x00, 0x00, 0x00};
expect[6] = msg.msg[2];
expect[7] = msg.msg[3];
return waitForString( fd, expect, 8 );
}
int main( int argc, char *argv[] ) {
int fd = openUART();
if( fd < 0 )
return 0;
int result = sendUBXMessage( fd, getStationaryMessage() );
if( result == 1 ) {
printf( "Stationary mode successfully set...\n" );
result = sendUBXMessage( fd, getSaveConfigurationMessage() );
if( result == 1 ) {
printf( "Configuration successfully saved...\n" );
}
else {
printf( "Failed to save configuration!\n" );
}
}
else {
printf( "Failed to send stationary message!\n" );
}
close( fd );
}
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