free GPIOs in the schematic?

Official Hardware Classic Yún
1

I saw the schematic http://arduino.cc/en/uploads/Main/arduino-Yun-schematic.pdf

There are free GPIOs shown, connected to a pin header. Where exactly are these pins on the board? Is there more information available?

It would really be useful for me, as I really need another serial interface on the linux side. (The 32u4 is to slowly, as I need 1 Mbit/s). If I could use linux side GPIOs, I could attach an extra UART hardware.

Thanks for any input,
Thomas

2

Highly unlike we could use GPIOs at Yun.

Yun's CPU AR9331 has only one UART, if you need more than one UART then different CPU is needed.

3

Please see this at http://arduino.cc/en/Main/ArduinoBoardYun

"The SPI pins are also connected to the AR9331 gpio pins, where it has been implemented in software the SPI interface. This means that the ATMega32u4 and the AR9331 can also communicate using the SPI protocol."

And just above: "Note that the SPI pins are [...] only available on the ICSP connector. "

If I understand this right, there are some AR9331 gpio pins available at the ICSP connector. This is an interesting finding, isn't it? Now, if we find an interrupt line from the AR9331 accessible, we can attach an external UART directly to the linux side.

4

Thomas33:
"The SPI pins are also connected to the AR9331 gpio pins, where it has been implemented in software the SPI interface. This means that the ATMega32u4 and the AR9331 can also communicate using the SPI protocol."
...

for my understanding after upgrade ( downgrade) Yun OS (kernel 3.3.8 from older one kernel 3.8.3) , above statement is no longer true.

Thomas33:
...
And just above: "Note that the SPI pins are [...] only available on the ICSP connector. "
...

It is hardwired with ATMega32u4 via ICSP, can't access directly.

Thomas33:
...
If I understand this right, there are some AR9331 gpio pins available at the ICSP connector. This is an interesting finding, isn't it? Now, if we find an interrupt line from the AR9331 accessible, we can attach an external UART directly to the linux side.

AR9331 has only one UART and hardwired with ATMega32u4. if we need more than one UART, we use CPU which has more than one UART. such like MT7620A.

5

for my understanding after upgrade ( downgrade) Yun OS (kernel 3.3.8 from older one kernel 3.8.3) , above statement is no longer true

I was not addressing the SW part of the statement, but the HW part. This won't change with a SW update.

It is hardwired with ATMega32u4 via ICSP, can't access directly.

Are you are sure to have read the quotings and understood the impact? It says "The SPI pins are also connected to the AR9331 gpio pins" and "the SPI pins are [...] available on the ICSP connector". I don't understand why you are trying to ignore these statements.

AR9331 has only one UART and hardwired with ATMega32u4. if we need more than one UART, we use CPU which has more than one UART. such like MT7620A

So you suggest to ripp away the AR9331 and plug in a MT7620A to the yun board?

6

You can use SPI to communicate between the Atheros and the 32u4.
It's something I'm working on porting from the current Linino to OpenWRT-Yun.

Linino has the SPI_TTY driver that you can use with the StreamSPI Arduino library. It requires you build OpenWRT-Yun yourself since you need to define the pins to use for SPI on the Atheros side and then compile the kernel module for the driver which creates an SPI device in /dev.

When the Yun was using Linino it had this by default in the image. I never got it to work properly then, but do now with my own setup.

The GPIO pins are somewhat available directly on the ICSP header, but more trouble than it's worth.

I needed GPIOs, extra USB and an Arduino with more memory so I ended up building a custom shield.

linux_shield.jpg