Re: general questions regarding ARMs


Schwob US wrote:
> You can program through serial interface or JTAG or parallel
> programmer, this is not ARM specific but more vendor specific and most
> of all tool specific. Using the high end tools will giove you the most
> headache because they usually do not provide direct download into flash
> software (e.g. Greenhills and ARM). Compilers from IAR and Keil however
> support many ARM devices from different vendors and you can directly
> download your code into the flash. afaik this is possible with Atmel
> flash.

Well I should mention I'm a college student (3rd year EE at UIUC) so I
was hoping to use some of the free tools out there. What options would
that leave me?

> This depends on tyhe memory (Flash) implementation. Wider memory
> intefaces such as the Philips 128-bit wide flash provide much faster
> execution than a 32-bit wide flash as implemented on the newer Atmel
> SAM7S devices and even more so than on the older devices which only
> have a 16-bit bus to the flash.

Right now I'm planning on using a SAM7X.

> In an embedded environment you execute usually from both memories. If
> your flash is slower than the clock rate and narrow, you should limit
> the code executed form there to non realtime critical code. You are
> talking about Linux, then all your code has to be non realtime critical
> ;-)

Oh - everything needs to be realtime for this. I thought there were
some special linux kernels designed to run real time code?

> No way! You need approx 4 MB of RAM to run Linux preferably 16 MB+

Any idea if that much RAM could be added to an Atmel ARM? I skimmed
through the data*** to see if it had any sort of external memory
controller - and I didn't see one, but I might not be looking for the
right thing.

> Basically DMA does in one cycle (get some data from location a and
> store it in location b) what otherwise needs a whole lot more cycles as
> the ARM architecture is a Risc based architecture. That means all data
> transfer goes through registers no memory to memory transfers (that's
> what the DMA is doing).

Got it. Thanks for your help!

-Michael

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