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Re: [avr-libc-dev] Is there interest in an arm-libc?


From: Szikra István
Subject: Re: [avr-libc-dev] Is there interest in an arm-libc?
Date: Sat, 08 Nov 2014 01:20:52 +0100
User-agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:31.0) Gecko/20100101 Thunderbird/31.2.0

Hi.

I'm also interested.

Maybe I expose my lack of knowledge here, but what is the point of running off 
RAM? Chips I used so far are pretty sparse on RAM, so one couldn't do there 
much, anyways. Would it be an option to simply ignore these paths in gcc, 
letting the user deal with such rare(?) setups? If one really needs this, one 
can always copy into RAM per user code and jump to it, of course.

At a certain frequency flash access time becomes an issue. I don't recall the exact frequency, but the SAM7x datasheet says this about flash:
Single Cycle Access at Up to 30 MHz
STM32F405 has similar data on Maximum Flash memory access frequency with no wait state.

Newer controllers have wide flash access, good prefetch cache, and branch prediction, so this might be less of an issue, but some hotspots can still benefit from running them from RAM.

Current consumption might be another factor.

Bootloaders with flash writing, where flash will be locked probably would need to be run partly from RAM (or using ROM subroutines).

But I think most users will be fine running their application from flash.

I might be wrong about some of this, and missing some other reasons.

Regards,
Steven



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