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Re: dma 8 bit peripheral





On Mon, 25 Nov 2002, Steve Jones wrote:

> I am putting a 8 bit wide NAND flash (Samsung) onto the ETRAX MMC chip. 
> These have a data bus but no address bus as such (address is written via
> data bus). I would like to use DMA as these devices have a page mode
> where the internal address auto increments (512 Bytes circular) to
> transfer data to and from it in 512 byte blocks from 16 Bit SDRAM.
> 
> Could I connect as follows
> CE#   CSR0, 
> WE#  WE0|CSR0
> RE#   RD|CSR0
> ALE    Gen IO
> CLE    Gen IO
> D0-D7    D0-D7
> 
> Set access to speed to 50nS etc.
> 
> ETRAX DREQ    to ETRAX General IO pin
> To use DMA use Burst Mode. Set DMA Counter to 512 bytes. Assert IO pin, 
> DMA should continue until counter hits zero where DMA should stop.
> Unassert IO pin to unassert DREQ. Would this work, or could I set DREQ
> to permanently asserted and use DMA counter to start and stop it etc.
> 

It should be possible to set DREQ permanently, and control the external
DMA with only the counter and start/stop bit.

The connection you have proposed will not work, since the CE# to the NAND
flash needs to be low throughout the operation. If you control the CE#
from a general IO instead, I think it will work.

Per Zander