AVR Freaks

For the time being I'm not using the external RAM, was hoping I could save the costs of the final design... That and I've never actually used external RAM haha. Probably worth me setting up and using it though, it will prove my theory about running out of internal RAM if nothing else. Thanks for the thought.

A nice idea but if possible I'd like to stick with the ATxmega128A1U as I already have the corresponding Xplained Pro, but using the external RAM I have available as you already mentioned should help me get around this.

Regardless of whether or not I use external RAM that's probably a good idea anyway, however I'll have to modify uGUI's source code to implement this but hopefully that won't be too much of a task.

Thanks for the suggestions, in truth if I start to find that an Xmega isn't quite up to the job of driving a touchscreen GUI then I'll either take it as an excuse to delve into the world of ARM, or I'll use an off-the-shelf item from 4D Systems.

Many thanks for all of your feedback and input!

Ahhh okay, thanks for the heads up. Could you point me in the right direction on how I'd go about invoking a post build step in AS7? It's not something I've ever actually had to do before.

Okay so I found the file and the tag you were referring too, and inside that tag are separate <address-space> tags for the different parts of memory. This is the one relevant for RAM...

<address-space name="data" id="data" start="0x0000" size="0x1000000" endianness="little">
  <memory-segment start="0x0000" size="0x001000" type="io" rw="RW" exec="0" name="IO"/>
  <memory-segment start="0x1000" size="0x000800" type="eeprom" rw="RW" exec="0" name="MAPPED_EEPROM"/>
  <memory-segment start="0x2000" size="0x002000" type="ram" rw="RW" exec="0" name="INTERNAL_SRAM"/>
  <memory-segment start="0x4000" size="0x00BFFF" type="ram" rw="RW" exec="0" name="EXTERNAL_SRAM" external="true"/>
</address-space>

The external SRAM's size entry seems incorrect to me. Given that with the starting offset of 0x4000, a size of 0x00BFFF would equate to 0x7FFF/ 32KB of external SRAM, and given that you can set the the block size for the 4 chip selects, via the ASIZE bits in their corresponding CTRLA registers, up to 16MB, surely the size entry should be much bigger? Even in my case where I'm only using 256KB the size entry doesn't add up. Can I simply change the value to suit or...?

Ah, okay that would explain a few things! So although I've set up the EBI to use 256KB of external SRAM, I can't actually access all of that - something which I did actually notice when debugging, as the memory window displayed everything above 0xBFFF as '??'.

So does that mean that  size="0x00BFFF"  is correct? How come it's not 0xFFFF? Is there something else that limits this?

Once again, thank you for your responses gchapman!

EDIT: Ah, of course the size is correct; 0x4000 + 0xBFFF = 0xFFFF. You'll have to excuse me for missing the painfully obvious there ha!