Use of memory in c++

Question

I'm not sure how to pose this question, but here it goes:

1. When programming on my Atmel MCU's in c++ I tend to mix the 'program'-variables and the 'user'-variables in the same datamemory. Which in time is a hassle because I want to make a few presets that can be loaded or saved. And I do not want the 'program'-variables saved because the program will generate the correct values based on the 'user'-values. Is it common practice to split that in memoryplaces? Eg. timercounter in PGM-Memory, thresholdByUser in DATA-memory?

2. In my program i've made several different functions which all have their own set of uservariables. Eg: settings has 5 uservariables, generator has 6 uservariables etc... Would you make 1 big array and then make #define settingsgeneratorSpeed 1, #define settingsBacklight 2 as places, so you could call them as such: Array[generatorSpeed], Array[settingsBacklight] or would you still split it up and collect them by using a struct orso?

Working on atmelstudio 4.0 with a ATMEGA644 on STK500.

Thanks for all the help you can give!

Answer 1

For question 2, I'd use const int& settingX = array[Xoffset] instead of a define. But that assumes there's some need to iterate though the array, else I'd just define separate variables.

Answer 2

Assuming you are using AT(X)Mega, when referring to Atmel MCU's: IIRC it depends which compiler suite you are using. With gcc, if you have something like a static int, it will go to PGM and it copied to RAM when the program runs. Hence, if you want your variables not to be in PGM memory, you must make them stack or heap variables. Constants and statics will always reside in both. If you wan't to have PGM constants only, you can specifiy that, but this requires special read operations.