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m1geo
Joined: 31 Dec 2008
Posts: 5
Location: London, England, UK
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| GPS 18F458 Hardware UART Problems |
 Posted: Wed Dec 31, 2008 12:39 am |
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Hello, and thank you for reading this post.
I have a problem with a project I'm starting out with. I am attempting to write a GPS logger to SD-card. I know its been done before many-a-time, but I am to improve on this at a later stage.
The PIC is running at 16MHz (no PLL), and displays the screen to the hitachi LCD no problem via (unmodified) LCD.C CCS driver. However, the PIC then locks/hangs/crashes in the delay following the splash screen.
By commenting out the "#use rs232(...)" statement, the program does not hang. This is only a very simple test program, and has no real use. I was intending for the code above to show how the RDA interrupt worked. I wasn't sure if it interrupted on a null character, line feed, carriage return, or for each character. This is what i aimed to find out. The other interrupt just gives approx 1s pulses. Both ISRs just increment a variable and the main routine updates the screen with the data.
As i touched on before, the program works fine without the "#use rs232(...)" statement, but dies with any mention of it.
I have never used the Hardware UART before, and so I may have completely gone around this the wrong way.
I also searched the CCS forums too, and found nothing detailing my problem (closest match; http://www.ccsinfo.com/forum/viewtopic.php?t=36875). I am really stumped by this. My initial thought was about the clock frequency. I am, as I say, unsure.
Any help would be greatly appreciated.
Kind Regards and Happy New Year to all!
George Smart, M1GEO
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This is the header file, Att1.h:
| Code: |
#include <18F458.h>
#device ICD=TRUE
#device adc=8
#FUSES NOWDT //No Watch Dog Timer
#FUSES WDT128 //Watch Dog Timer uses 1:128 Postscale
#FUSES HS //High speed Osc (> 4mhz for PCM/PCH) (>10mhz for PCD)
#FUSES NOPROTECT //Code not protected from reading
#FUSES NOOSCSEN //Oscillator switching is disabled, main oscillator is source
#FUSES NOBROWNOUT //No brownout reset
#FUSES BORV20 //Brownout reset at 2.0V
#FUSES PUT //Power Up Timer
#FUSES NOCPD //No EE protection
#FUSES STVREN //Stack full/underflow will cause reset
#FUSES DEBUG //Debug mode for use with ICD
#FUSES NOLVP //No Low Voltage Programming
#FUSES NOWRT //Program memory not write protected
#FUSES NOWRTD //Data EEPROM not write protected
#FUSES NOWRTB //Boot block not write protected
#FUSES NOCPB //No Boot Block code protection
#FUSES NOWRTC //configuration not registers write protected
#FUSES NOEBTR //Memory not protected from table reads
#FUSES NOEBTRB //Boot block not protected from table reads
#use delay(clock=16000000)
#use rs232(baud=4800,parity=N,xmit=PIN_C6,rcv=PIN_C7,bits=8)
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This is the main program file, Att1.c
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#include "Z:\Electronics\GPS\Att1.h" // file/code posted above
#include <LCD.C>
#ZERO_RAM
int times;
int rda;
#int_RTCC // every 1 second
void RTCC_isr(void) {
times++;
}
#int_RDA // receive data available
void RDA_isr(void) {
rda++;
}
void main() {
setup_adc_ports(NO_ANALOGS);
setup_adc(ADC_OFF);
setup_psp(PSP_DISABLED);
setup_spi(SPI_SS_DISABLED);
setup_wdt(WDT_OFF);
setup_timer_0(RTCC_INTERNAL|RTCC_DIV_64);
setup_timer_1(T1_DISABLED);
setup_timer_2(T2_DISABLED,0,1);
setup_timer_3(T3_DISABLED|T3_DIV_BY_1);
setup_comparator(NC_NC_NC_NC);
setup_vref(FALSE);
lcd_init();
enable_interrupts(INT_RTCC);
enable_interrupts(INT_RDA);
enable_interrupts(INT_LOWVOLT);
enable_interrupts(GLOBAL);
output_high(PIN_D3); // turns on the LCD backlight
lcd_putc('\f'); // clear screen
delay_ms(5);
printf(lcd_putc, " GPS Logger \n Attempt 1.00 ");
delay_ms(2000);
while(true) {
printf(lcd_putc, "\fRDA: %u\nTIME: %u", rda, times);
delay_ms(250);
}
}
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_________________
George Smart
Student in Electronic & Electrical Engineering
University College London |
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PCM programmer
Joined: 06 Sep 2003
Posts: 21708
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| Posted: Wed Dec 31, 2008 1:04 am |
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| Quote: |
#int_RDA // receive data available
void RDA_isr(void) {
rda++;
}
By commenting out the "#use rs232(...)" statement, the program does not hang. |
You need to read the character from the UART to clear the interrupt
condition. Use getc() to do this, inside the isr. |
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m1geo
Joined: 31 Dec 2008
Posts: 5
Location: London, England, UK
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| GPS/NMEA String Handling |
| Posted: Wed Dec 31, 2008 10:20 am |
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PCM programmer, thanks for your reply. Guess that kinda answers the other questions too 
One other quick question, as i wish to read NMEA data, which is terminated by "<CR><LF>". Is it possible to get the data using the gets(), as opposed to your suggestion of getc().
For example
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struct {
char data[128]; // uart data dumped in here, to work on
int element; // position in the array
int1 new; // flag for new raw data
} gpsraw;
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Then using this
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#int_RDA // receive data available
void RDA_isr(void) {
gets(gpsraw.data);
}
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Will this handle the reading in of a string, rather than char-by-char?
Any help, greatly appreciated!
_________________
George Smart
Student in Electronic & Electrical Engineering
University College London |
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FvM
Joined: 27 Aug 2008
Posts: 2337
Location: Germany
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| Posted: Wed Dec 31, 2008 10:42 am |
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| gets() can't be used in a receiver interrupt in a meaningful way. You can use it e. g. with a user defined stream, that get it's receive buffer filled in an ISR. Simple CCS examples are using gets() with a polled UART, in applications, that have nothing to do but waiting for UART input. |
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m1geo
Joined: 31 Dec 2008
Posts: 5
Location: London, England, UK
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| Posted: Wed Dec 31, 2008 11:59 am |
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FvM, many thanks for your reply.
I kind of realized this by looking at the source code, but thanks for the confirmation. I have basically just implemented a char array where I read data into it whenever the RDA ISR is run. This then also checks for the CR/LF ending, and sets a new-data flag.
| Code: |
#int_RDA // receive data available
void RDA_isr(void) {
char c;
c = getc();
if (c != 13) { // if the char is not a CR
if (c != 10) { // if the char is not a LF
gpsraw.data[gpsraw.element] = c; // put in the array
gpsraw.element++; // next element in the array
}
} else { // if the char is a CR
gpsraw.new = TRUE; // thats the end of what we expect, new data available
gpsraw.element=0; // get back to the beginning.
}
}
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Here, the gpsraw structure is as before, in my previous posts.
Many thanks both for your help. It was greatly appreciated
Happy New Year.
_________________
George Smart
Student in Electronic & Electrical Engineering
University College London |
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