Storing a variable to program memory during run-time

[cbarberis]

I have been having issues with some calibration constants that are stored in internal eeprom, ocassionally getting corrupt, so I though of a secondary method where I could also store the same variable in a high location of program flash rom memory, where I could retreive it in case of eeprom corruption, this of course is just a backup in case the value of the variable that is stored in eeprom gets corrupted. Because I never have tried the CCS routines; write_program_memory() and read_program_memory, I wrote a simple test routine (below) to take a float variable store it in a rom location and then pass the value to another float variable. So far, this does not seem to work as both variables actually get blown away, so I guess that my method is quite flawed. Was wondering if anyone has implemented something similar that works?

*************************************************************

#include <18F6720.h>
#device ICD=TRUE
#device adc=10

#fuses HS,PUT,BROWNOUT,WDT128,NOLVP,NOWRT,DEBUG,STVREN // for ICD
#use delay(clock=10000000,RESTART_WDT)


#define ROMCALOC 0x186A0
#org ROMCALOC,0x186C0 {} // put this here to reserve the loc

void init()
{
setup_psp(PSP_DISABLED);
setup_adc_ports(AN0|VSS_VDD);
setup_adc(ADC_CLOCK_INTERNAL);
setup_wdt(WDT_OFF);
setup_timer_3(T3_DISABLED|T3_DIV_BY_1);
setup_timer_4(T4_DISABLED,0,1);
disable_interrupts(INT_TIMER0);
disable_interrupts(INT_TIMER1);
disable_interrupts(INT_EXT);
disable_interrupts(INT_EXT1);
setup_comparator(NC_NC_NC_NC);
setup_vref(FALSE);
setup_low_volt_detect(FALSE);
setup_oscillator(False);
disable_interrupts(GLOBAL); }


void main()
{
float SpanFactor = 0.0023842; // var to be written to memory
float TestFloatVar =0; // var to read from memory

init();

write_program_memory(ROMCALOC, SpanFactor, sizeof(SpanFactor));
delay_us(1);
read_program_memory(ROMCALOC, TestFloatVar, sizeof(TestFloatVar));
delay_us(1);




do { restart_wdt(); } while(1);
}

[SET]

[Ttelmah]

You need to give the read and write routines, the _addresses_ of the variables. For an _array_, the name of a variable, is it's address, but for a normal variable it isn't. You are writing to an address defined by the bytes making up the value '0.0023842', treated as an integer, and reading from a random address,defined by what just happens to be in 'TestFloatVar'...
Use the '&' function, to get the variable addresses, and it should all start working.

Best Wishes

[cbarberis]

I should have known better; to either use a pointer or the address of such variables. Also I meant to use #org ROMCALOC, 0x186A2 as a write to program memory sets aside 8 consecutive bytes for a write.

Thank you for your help Ttelmah!!

It now works exactly as I wanted it, I am wondering if I really need to have the #org statement, supposedly with it, the compiler will not place anything on that location??

[Ttelmah]

As a completely different way of doing it, just declare a #ROM value at the location. If you declare it as a float, you can even initialise the values in the declaration. This both puts the declared values at this point, and reserves the memory, at the same time.

Best Wishes

[cbarberis]

using something like: #ROM float ROMCALOC = {0xCDE93276} // to store 0.00273
This does not seem to work, actually I get an error during compilation under the float declaration "Expression must evaluate to a constant" If I recall when using the #ROM it defaults to a 16 bit constant on the PCH parts and a byte for the PCM parts, however you can declare a byte for the PCH part as a #ROM int8 address {const value}

Did I missinterpret your previous sugestion?