Why does Flash build not use all of RAM?

(3 posts) (2 voices)

bobc
Member

I'm working on port of libmaple into Arduino 1.5.x IDE environment. This is going quite well, but there is one question I am puzzling over.

Namely, in the link script (e.g. mem-flash.inc), the first part of RAM (0xC00 bytes) is reserved (presumably for the bootloader). I don't see why this is necessary, the bootloader and application will always initialise RAM in their startup code, and as far as I can see there is no communication between bootloader and application via RAM that would need RAM contents to be preserved.

Perhaps there is a reason somewhere I haven't spotted, but I will try changing it to see what happens.

I'd also like to reduce the amount of Flash used by the bootloader, but that is another topic!

Posted 1 year ago #
gbulmer
Moderator

I have a very vague recollection that reserving some RAM allowed the bootloader to be triggered by a reset, without disturbing a program loaded into RAM. So that RAM-resident program could be reentered repeatedly via a reset to the bootloader.

But I can't find any reference that look familiar enough to explain why I think that, so I may be wrong.

Posted 1 year ago #
bobc
Member

Sure, that makes sense for a RAM build, the bootloader must load it into RAM while the bootloader is running.

I can't see why a Flash build would need the same behaviour though.

Posted 1 year ago #

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