4-bit SD Card mode

[Björn König]

Neil wrote:
> 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.

Björn