I hope this is an okay group to ask this in, if not I apologise. (and could someone point me to a better location)
I just got my deign up and running using an AVR Mega128. For some odd reason it looks like my stack is disabled. Within AVRStudio the stack monitor has all of the stack entries grayed out and each is labeled "disabled".
It looks like everything is set up correctly. The grayed out fields on in AVRStudio might be that limits are disabled. In any case, when I step through my code everything seems to work, the stack pointer changes correctly but on a return from subroutine I head off into the woods.
I am not using external SRAM and it almost looks like the code is trying to use it.
I am using this asm code to set up the stackpointer. ramend is at 0FFF'h for atmega 103 and 128 reset: ; ************* Stack Pointer Setup Code ldi wl,high(ramend-5) ; Stack Pointer Setup out SPH,wl ; Stack Pointer High Byte ldi wl,low(ramend-5) ; Stack Pointer Setup out SPL,wl ; Stack Pointer Low Byte
It appears that your fuse bits are still in compatibility mode i.e. pretending that you are using an Atmega 103.
...Well, certain odd problems arise out of the situation that the AVR devices as shipped by Atmel often come with a default fuse bit configuration that doesn't match the user's expectations. Here is a list of things to care for:
.... . The ATmega128 ships with the fuse enabled that turns this device into ATmega103 compatibility mode. This means that some ports are not fully usable, and in particular that the internal SRAM is located at lower addresses. Since by default, the stack is located at the top of internal SRAM, a program compiled for an ATmega128 running on such a device will immediately crash upon the first function call (or rather, upon the first function return). .... /Roland