[OpenWrt-Devel] Multipurpose pins not locked on WRT3200ACM

Hartmut Knaack knaack.h at gmx.de
Tue Jul 3 06:08:15 EDT 2018

I was curious if there are some GPIOs exposed on the Linksys WRT3200ACM, so
I started exporting them in /sys/class/gpio. I realized, that some are
locked against exporting (those claimed by gpio-leds and gpio-keys, power
regulator), while others exposed more or less problematic side effects.
Less critical are GPIOs 2 and 3, which seem to be used by the I2C bus,
where a LED driver controls some of the front LEDs.
A number of other GPIOs (22, 23, 25, 28, 30, 32, 33, 35, 56, 38, 40, 41,
42) however had an effect on the NAND-flash in the range of just not being
able to access it for the moment up to corrupt firmware partition (with the
need to unbrick from the boot loader) and even to the point, that it
requested bootloader code on the uart. It seems, GPIO 33 does major
corruption and GPIO 36 can be really nasty.
There are two more GPIOs, which are quite interesting: when GPIO 26 is
exported and set to output, setting its value to 1 causes all LAN LEDs to
light up constantly. May it be connected to the switch chip?
GPIO 52, when exported and set to output, also causes the LED driver on I2C
to not respond any more. What is the reason (connected to a reset line?)
The basic conclusion is: those multipurpose pins in use need to be locked,
just like the gpio-leds and gpio-keys modules do.
The question remaining is: which multipurpose pins are already in use by
NAND-flash, I2C bus, UART0, SATA(?), PCIe(?), some ethernet MII(?) or
something else?

@Imre Kaloz: From what I remember, you had a closer relationship to Linksys
and brought in support for this device (family). I hope you can shed some
light on this issue.


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