4-bit SD Card mode

Neil Bradley nb at synthcom.com
Thu Jun 7 09:39:13 UTC 2007

>> I've done SD drivers, both 1 and 4 bit, DMA and programmed I/O, on the
>> PXA270, Atmel SAM7, Atmel SAM9, and Freescale MX31 CPUs. How may I be of
>> assistance?
> Actually the driver does the whole status and error handling using an
> interrupt service routine. This is unsuitable in 4-bit mode because in
> this mode the interrupt line is shared with a data line. So to get 4-bit
> mode working it is necessary to know the complete definition of the
> "interrupt period" - the period where it is allowed to enable the
> interrupt during 4-bit mode.

Hm... I haven't ever heard of nor needed to consider such a thing in any 
of my implementations. The controllers I've encountered all have a "1 
bit/4 bit" mode setting, and as long as you tell the card to go in to 4 
bit mode and set it in the hardware as well, the SD controller handles 
everything for you.

What is the CPU in question?


C. Neil Bradley - KE7IXP - The one eyed man in the land of the blind is not
                            king. He's a prisoner.

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