SDIO multiplexing

[joerg at openmoko.org]

Wolfgang Spraul schrieb:
> Hi there,
> we played with a number of ideas on the HW side, one of them was around
> how we can extend the lifetime of gta02, by making some fixes.
> Such as removing the glamo chip. Which would leave no SDIO for the Wi-Fi
> module.
> Do you have any ideas how this could be fixed, i.e. how we could remove
> the glamo on gta02 and still have Wi-Fi?
> Sean and I met Harald at the Open Hardware Summit conference, and he
> suggested this 'hack':
> 
> http://www.altera.com/literature/an/an509.pdf
> http://www.fairchildsemi.com/ds/FS/FSSD06.pdf
> 
> Basically a form of SDIO multiplexing.

Seems to me like threre is little chance (or high effort tricky coding) to 
have the system code on one SD card, and by executing this code accessing the 
other card in the same moment. Basically you had to copy some code stub to 
RAM which is doing the multiplexing, so you can switch your own system code 
out of address space. Strong impact to throughut/bandwidh due to permanent 
switching between the 2 SD-cards.
All this applicable for the idea "Ommit flashrom(NAND, NOR), system resides on 
SD-card" - probably you had to put up with rejecting this concept then.

> Other options would be SPI.
> What do you think of the multiplexing, SPI, or other ways to achieve this?

from: http://en.wikipedia.org/wiki/Serial_Peripheral_Interface_Bus
''The Serial Peripheral Interface Bus or SPI (often pronounced "es-pē-ī" [IPA: 
ɛs pi aɪ] or "spy" [IPA: spaɪ]) bus is a synchronous serial data link 
standard named by Motorola that operates in full duplex mode. Devices 
communicate in master/slave mode where the master device initiates the data 
frame. Multiple slave devices are allowed with individual slave select (chip 
select) lines.''

"Multiplexing" SPI is perfectly feasible :-). No big issue in it anyway I 
think. No idea about the availability of SPI-IF solutions for our SDIO-based 
modules though.

cheers
jOERG