Question about flash

ellensp

Absolute beginner when it comes to FPGA's here..

On the board is 256Mbit Serial Flash and 16Mbit Serial Flash

Basically nothing seem to have been mentioned these?

As I understand it the FPGA doesn’t need external flash (well thats the impression the over view seems to give), so are these just for storage for projects?
Or is the configuration settings for this FPGA external?

Thanks

Peter

jpiat

Hi,

the logipi only has a 16Mbit serial flash. This flash can be used to retain the FPGA configuration so that is loaded on power-up instead of being loaded from the Raspberry-Pi. This flash could additionally be used to store data for your architecture. We haven't used it so far, because we found out that loading the FPGA from the raspberry-pi was very convenient and could event be done by a script at linux startup. Be sure taht at some point we will propose an application using this external flash.


Regards,

Jonathan Piat

mjones

Hi Peter,

Sorry for the confusion.  I just found that the quickstart guides labeled the parts as you just described, which is incorrect.  I have fixed them in the wiki.

The 2 types of memory on the LOGI board:

•  256Mb of SDRAM which is high speed and high density memory that is typically used for to buffer data that is needed very quickly.  This memory is volatile, loses it state when powered down, is much faster than flash memory, more complex to use than flash.  
  
• 64Mb of Flash memory is non-volatile (keeps state after removed power).  The flash was intended to be an optional method of storing a bitstream that the FPGA can load itself from on bootup.  Or the flash can be used as general purpose flash memory for storage.  

Hope this helps.

Cheers,

Mike

JFrodsham

I can give you a good example of why you might want to use the SPI flash.  You can get the FPGA up and running in milliseconds.  We were running a Microblaze with a Linux kernel and the FPGA could perform its functions autonomously once Linux booted.  If you program from the Pi or BB, you have to wait for the Arm Linux to boot before your FPGA can begin loading.  It really just depends on what your design goals are.

-J