Re: [avr-gcc-list] Save RAMPZ register in interrupt handler routines

[Dmitry K.]

Hi.

Alas, there is a circumstance which does preservation of register RAMPZ
obligatory. At least, obligatory by default. The 128KB-flash crystal has
semidocumented feature (IMHO, bug): at performance of reading from memory
the command 'LD R,Z+' modifies the RAMPZ register in case of wrapping. The
same is for other 3 combinations (ST, -Z). I have checked up it on the
AT90CAN128.  Thus, absolutely harmless pure C code, like
       while (*dst++ = *src++);
where both of a file are located in the SRAM, can destroy the RAMPZ if
one of arrays is located with edge.

Strictly speaking, absence of preservation of the RAMPZ (by default)
is a mistake which should be corrected in all Avr-gcc versions.

Let's notice, that in all known crystals the RAMPZ does not influence 
in any way operations from the RAM.

Dmitry.