SPI-Driver_quick2wire_chip-select

[Peter]

Hi!

I’ve got a question concerning the spi chip-select.

I want to connect more than two spi-modules with the Raspberry Pi.

Is it possible to use normal GPIO-Pins for Chip-Select? Raspberry has got only two...

And if it is possible, how do I have to change the quick2wire-spi driver?

 

Thanks a lot!

 

Greets,

Peter

[Geoff Drake]

Hi Peter

If you want to connect 4 or less devices you could implement a 2-4 decoder, and yes you could use the GPIO lines.

I have not looked at the spi code, so I do not know what changes would need to be made.

Cheers

Geoff

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[Andrew Scheller]

I just had a look at
https://github.com/quick2wire/quick2wire-python-api/blob/master/quick2wire/spi.py
and all the __init__ function does is:
self.fd = posix.open("/dev/spidev%i.%i"%(bus,chip_select), posix.O_RDWR)
so it's the spidev driver that would need to be changed, not the
quick2wire code.

I did a quick google, and this comment confirms that it's the kernel
driver that would need to be modified:
https://projects.drogon.net/understanding-spi-on-the-raspberry-pi/#comment-582

It looks like the kernel SPI driver is in
https://github.com/raspberrypi/linux/blob/rpi-3.6.y/arch/arm/mach-bcm2708/bcm2708.c
with the low-level SPI controller documented in the BCM2835 'datasheet'
http://elinux.org/RPi_Hardware#Components

However (and I don't know very much about SPI here, so I'm just
guessing) maybe you could always write to SPI channel 0, but then
ignore the built-in chip-select lines, and do the multiple
chip-selects you need yourself with regular GPIOs? (You'd obviously
need to ensure that you didn't accidentally enable two different chips
at once)

Andrew

[Peter]

Hi Guys!

 

Thanks for your quick response!

I will continue searching, but nevertheless I now know what I have to search for ;)

 

Peter