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AndrewS
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Compute Module GPIO pins & functions

Wed Jun 25, 2014 2:28 pm

I've now updated http://elinux.org/RPi_BCM2835_GPIOs to show how the BCM2835 pins are connected on both the Compute Module and the Compute Module IO Board :D :geek:

seulater
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Re: Compute Module GPIO pins & functions

Tue Aug 05, 2014 2:18 am

I am using the SPI pins on the CM kit.
The way i read your table for the SPI0 pins are

SPI0_CE0_N = J5-17
SPI0_MISO= J5-19
SPI0_MOSI= J5-21
SPI0_SCLK= J5-23

Yet i got nothing on those pins.
Took the scope out and found the pins that work for SPI0 are:
SPI0_CE0_N = J5-8
SPI0_MISO= J5-9
SPI0_MOSI= J5-10
SPI0_SCLK= J5-11

Am i just reading you page wrong, or is there a mistake there.

[EDIT] I was reading this wrong.
Just in case others made my mistake, the labels in the column called "CM IO Board connection" are not what is printed on the silk screen (the white labels) for J5, but rather the actual pin numbers of J5.
Last edited by seulater on Tue Aug 05, 2014 2:56 am, edited 1 time in total.


svrsig
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Re: Compute Module GPIO pins & functions

Tue Aug 05, 2014 11:10 am

Does that mean that the EMMC lines CLK CMD D0 D1 D2 D3 are GPIO 48 to 53 so that software that controls an SD card on model B+ using GPIO 48 to 53 should just work 'out of the box' on the Compute module? Or is there some subtlety required?

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AndrewS
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Re: Compute Module GPIO pins & functions

Tue Aug 05, 2014 12:32 pm

svrsig wrote:Does that mean that the EMMC lines CLK CMD D0 D1 D2 D3 are GPIO 48 to 53 so that software that controls an SD card on model B+ using GPIO 48 to 53 should just work 'out of the box' on the Compute module?
Exactly :)
Or is there some subtlety required?
I believe it works 'out of the box' on Linux (since the kernel includes both SD and eMMC drivers), but it appears there's some subtle difference between SD and eMMC when it comes to RISC OS? :? http://www.raspberrypi.org/forums/viewt ... 04#p589404
(oh, didn't realise that was you too!)

I'm afraid I dunno what those 'subtle differences' are myself.

svrsig
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Re: Compute Module GPIO pins & functions

Tue Aug 05, 2014 3:48 pm

I'm sure the differences are minor it is just difficult to see how to change the source code when it should 'just work'. The source has already been updated to allow for the fact that the card detect line has gone (model B+ and CM) which lost hardware detection of card removal (now done in software). Not sure whether the 'pull up' arrangements have changed now that the connection to the emmc is direct soldered rather than via the PCB to an SD card holder.

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AndrewS
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Re: Compute Module GPIO pins & functions

Tue Aug 05, 2014 4:14 pm

No idea if it'll be helpful or not, but did you already try looking through https://www.google.co.uk/search?q=diffe ... d+and+emmc :?:

Comparing http://www.raspberrypi.org/documentatio ... /README.md and http://www.raspberrypi.org/documentatio ... ematics.md indeed shows that the pull-up arrangements are different (and it looks like the eMMC runs at 1V8 vs the SD card which runs at 3V3), but I suspect that these hardware differences are irrelevant, and there's probably some kind of initialisation sequence which is different between the two. But I'm clearly just guessing...

svrsig
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Re: Compute Module GPIO pins & functions

Tue Aug 05, 2014 8:23 pm

and there's probably some kind of initialisation sequence which is different between the two
How does one find out what that is please?

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