Re: [avr-libc-dev] [task #3693] Add new devices: mega 640-1280-1281-2560-2561

[Paul Schlie]

> From: Bertolt Mildner <address@hidden>
>> Am Tuesday, March 15, 2005 um 12:13:56 PM hast du geschreiben:
>> Follow-up Comment #4, task #3693 (project avr-libc):
> 
>> According to the datasheet, all these devices (not just 256x - 640/128x too!)
>> store a 3-byte PC on stack.  This means they all need GCC changes (new
> 
> Yes, the datasheet can lead to this conclusion, but it would not make
> much sense.
> 
> If the IAR Tools are right then only the 256x uses 3-byte addresses on the
> stack.
> 
> IMHO, the current datasheet does a very very bad job on pointing out
> all the (small but mostly vital) differences between 640/128x and
> 256x!
> 
> Another example is in the "Instruction Set Summary". It says that CALL
> takes 5 clocks, but i would be very surprised if this holds true for
> 640/128x (64 and 128 take 4 clocks per CALL).

- too bad Atmel didn't simply choose simply require function entries be
  aligned on 2-word FLASH memory boundaries for these devices, thereby also
  eliminating the need for extended call and jump instructions as well (as
  it would have kept things both simpler and faster, at the cost of a likely
  very small FLASH utilization inefficiency).