Maximum SPI Devices

[GrubbyHalo]

There were rumors of the standard SPI driver being updated to support more than the current limit of two via the use of arbitrary GPIO pins used for CS. Does anyone know if progress has been made ?

Cheers

[mikronauts]

If you want to add your own SPI i/o expanders, see my article

http://www.mikronauts.com/raspberry-pi/ ... and-howto/

which allows eight SPI devices per chip select.

If you want more off-the-shelf SPI based boards (tft etc) even a new driver would not help, as the drivers for those devices would not be set up for additional (or expanded) chip selects.

There were rumors of the standard SPI driver being updated to support more than the current limit of two via the use of arbitrary GPIO pins used for CS. Does anyone know if progress has been made ?

Cheers

[msperl]

Assuming you use the Linux kernel:
If you add

Code: Select all

gpio-cs = <&gpio 8>, <&gpio 7>,<&gpio 22>;

to the devicetree, then gpios 8, 7 and 22 will be used for CS 0,1 and 2. Add more until satisfied...

[joan]

Assuming you use the Linux kernel:
If you add

Code: Select all

gpio-cs = <&gpio 8>, <&gpio 7>,<&gpio 22>;

to the devicetree, then gpios 8, 7 and 22 will be used for CS 0,1 and 2. Add more until satisfied...

Slightly sorry to hijack this question.

@msperl

Could you summarise the capabilities of the current spi_bcm2853 driver (i.e. arbitrary slave selects, interrupt driven, polling, DMA, auxiliary SPI device).

I don't think the auxiliary SPI is currently supported. If not, have you any feel for when it might be supported by the Pi Linux driver?

[GrubbyHalo]

Assuming you use the Linux kernel:
If you add

Code: Select all

gpio-cs = <&gpio 8>, <&gpio 7>,<&gpio 22>;

to the devicetree, then gpios 8, 7 and 22 will be used for CS 0,1 and 2. Add more until satisfied...

Hi Martin. This is what i was looking for. Thank you

[dwelch67]

this is a bare metal forum.

[fsr]

I don't think the auxiliary SPI is currently supported. If not, have you any feel for when it might be supported by the Pi Linux driver?

It was accepted into the next raspbian kernel (4.4.x)
https://github.com/raspberrypi/linux/co ... b239b1fd1f

[joan]

I don't think the auxiliary SPI is currently supported. If not, have you any feel for when it might be supported by the Pi Linux driver?

It was accepted into the next raspbian kernel (4.4.x)
https://github.com/raspberrypi/linux/co ... b239b1fd1f

Thanks.

I'm running 4.4.4-v7+ #850 on a Pi3 so gave it a go.

I just added dtoverlay=spi1-3cs to /boot/config.txt.

Unfortunately it won't boot with that line. Do you know of any gotyas?

[gchirico]

Hi Joan,
I too have the same problem with SPI1 aux on RBPi 3.
If I add "dtoverlay=spi1-3cs" to /boot/config.txt the RBPi3 won't boot.

I'm running 4.5.2-v7+ on a Pi3 so gave it a go.

Are you able to solve the problem ?

Thanks in advance,
Giovanni

[joan]

Hi Joan,
I too have the same problem with SPI1 aux on RBPi 3.
If I add "dtoverlay=spi1-3cs" to /boot/config.txt the RBPi3 won't boot.

I'm running 4.5.2-v7+ on a Pi3 so gave it a go.

Are you able to solve the problem ?

Thanks in advance,
Giovanni

Not directly. My solution is to use my pigpio library which supports both SPI devices. See http://abyz.co.uk/rpi/pigpio/cif.html#spiOpen

[gchirico]

Hi Joan,
thanks for the information.

Best Regards,
Giovanni

[dwelch67]

still a bare metal forum...

[fsr]

Unfortunately it won't boot with that line. Do you know of any gotyas?

Hi Joan,
looks like there is a conflict between the Aux Uart (UART1) and Aux SPI (SPI1) on the PI3 B. Still looking into it but disabling the Bluetooth (and therefore reverting the Uart config back to PI1/2) seems to work around the issue.

viewtopic.php?f=29&t=146291&p=977167#p977167

[joan]

@fsr Thanks.

[Cancelor]

Is the question 'how many chip selects can be defined' a pure numbers question?
There must be an electronic limit to what the SPI bus can drive.
I don't know the right terms but I'm thinking of things like attenuation, jitter, propagation and impedance.

[rzusman]

Fan-out is the term.
It's the number of inputs a single output can drive. For most ICs, it's typically "a handful."
You would also have to worry about signal integrity due to reflections caused by impedance mis-match, but that's not usually a big deal for slow, short-length signaling like SPI.