For certain combinations of AVR processor variants and memory models, the .xcl file examples by default use external memory for the stack, by having the following line active:
This means that calls to "?C_STARTUP" are redirected to "?RSTACK_IN_EXTERNAL_RAM" which is an alternative entry point in cstartup. The effect is that an SFR is set to use certain ports as external address and data bus.
External RAM is initialized in low_level_init. The activation of this line in the .xcl file is only required if RSTACK is placed in the external RAM.
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