Does I_MEM survive reset?

[DL8]

Does I_MEM survive reset? I assume D_MEM doesn't, but I assume I_MEM does. Is that correct?

[amichai-bd]

I_MEM and D_MEM will behave the same in reset.

If its "Worm Reset" Meaning VCC (Power) always is on and only the reset bit is triggered, the D_MEM & I_MEM will maintain their values.

incase of a "cold reset" both D_MEM & I_MEM will have "garbage". (which is expected when we lose power.

[DL8]

Garbage in case of cold reset is acceptable.

As for warm reset, the current behavior is problematic with global data: usually global variables are loaded into memory and usually the application won't explicitly initialize them. In our case, if a global variable was modified, its new value will remain after warm reset instead of the expected initial value.

The easy solution I can think of is to document that all global variables must be explicitly initialized in global setup handler, but that's a bit of a pain. Also, the compiler may decide to add data section and use it as baseline (see the case of a big array, where ".rodata" section is created and data is copied from there).

The more thorough solution I can think of is something like this:

1. Put all initial data (e.g. ".rodata", initialized global variables) in a dedicated read-only place. It could be stolen from I_MEM or a dedicated "data ROM" (read-only by convention, just like I_MEM. I prefer this solution because it's a healthier practice not to mix code and data)
2. Initialization code copies initialization data into global data and user code uses it (insert linker tricks here)