Saving a variable in between runs.

[pi_guy578]

Am I mistaken by saying if you initialize a static variable such as static int inBetween and it will store the varaible into the program, instead of the RAM. That is the ANSI C standard AFAIK, I'm not sure if its different on PIC chips... Can someone clarify?

Jake

[colt527]

Originally Posted by pi_guy578

Am I mistaken by saying if you initialize a static variable such as static int inBetween and it will store the varaible into the program, instead of the RAM. That is the ANSI C standard AFAIK, I'm not sure if its different on PIC chips... Can someone clarify?

Jake

Yes this is all well and good if you variable is not going to change in mid run, then use that same value again in the next rounds. This EEPROM is used for people who need to dynamically change variables and use them at a different time.

I'm using it to store p1_x values that a gyro calculated to make it go strait. Then next time I hit forward on the joystick it would start off with the calculated p1_x value instead of default 127. This (hopefully) will eliminate any beggining turning while the gyro is building up error.

[pi_guy578]

Originally Posted by 527Paranoia

Yes this is all well and good if you variable is not going to change in mid run, then use that same value again in the next rounds. This EEPROM is used for people who need to dynamically change variables and use them at a different time.

I'm using it to store p1_x values that a gyro calculated to make it go strait. Then next time I hit forward on the joystick it would start off with the calculated p1_x value instead of default 127. This (hopefully) will eliminate any beggining turning while the gyro is building up error.

As far as I can tell it would make no difference then b/c the program memory is also an EEPROM (or similar, can't remember) except the storing is auto handled instead of doing it manually using the user EEPROM where you can make errors.

[Mark McLeod]

Originally Posted by pi_guy578

Am I mistaken by saying if you initialize a static variable such as static int inBetween and it will store the varaible into the program, instead of the RAM. That is the ANSI C standard AFAIK, I'm not sure if its different on PIC chips... Can someone clarify?

Jake

There are three basic types of storage available to you on the PIC.

1) "static int x;" uses RAM or data space just as "int x;" does. You can change the value of x from within your program while it's executing (e.g. "x=y+2;"), but the value only lasts as long as the RC is on. All data is lost or returns to initialized values when the RC is turned off or reset.

2) "rom const int x=10;" uses ROM or program space. You cannot change the value of x from within your program as it's running (the compiler will reject "x=y+2;" as an error). The value at program load is permanent and unchanging, only by downloading a new program can x be modified. I believe this is what you were thinking of.

3) EEPROM requires special read/write commands to access as noted above. The value can be changed from within the program while it's running and the latest value is still there after the RC has been turned off or reset. This retention of a changable value is the reason people go to so much trouble to use the EEPROM r/w commands.

[pi_guy578]

Originally Posted by Mark McLeod

"static int x;" uses RAM or data space just as "int x;" does. You can change the value of x from within your program while it's executing (e.g. "x=y+2;"), but the value only lasts as long as the RC is on. All data is lost or returns to initialized values when the RC is turned off or reset.

Whoops, my mistake, a static variable stays initialized between function calls but not neccessarily program runs.