ESP32 Forum

I'm testing ethernet with the ESP32-PICO-KIT + Waveshare LAN8720 module.

I got ethernet working as per https://sautter.com/blog/ethernet-on-es ... g-lan8720/ but I now want to use GPIO0 as clock output instead of input.

To achieve this, I removed R12 and R14 resistors on the waveshare board and jumped between R12 and R14 with one of the 33ohm resistors so that the R_RXCLK pin on the board is connected to the CLKIN pin of the chip through the 33ohm resistor.

I changed one line of the code to read "config.clock_mode = ETH_CLOCK_GPIO0_OUT".

On trying this code i get the error "emac: Timed out waiting for PHY register 0x2 to have value 0x0007(mask 0xffff). Current value 0xffff". On checking with an oscilloscope, i do not see any clock generated on the GPIO0 pin.

What am I doing wrong? Any help is appreciated.

Which esp-idf version do you use?

WiFive wrote: ↑

Sun Jun 16, 2019 2:48 pm

Which esp-idf version do you use?

git master.
$ git describe
v4.0-dev-837-g58df1d93b

Just to be sure, I checked out release/v3.2 and switched the compiler to recommended version (5.2) but the problem is the same.

Does the 50MHz clock have any relation to configuring the lan8720? Why does register setup fail when I disconnect the oscillator? I can see the clock on the scl line.

Is there anyway to debug this? I would like to avoid the extra pin to enable the oscillator and the cost of the oscillator itself. Hence, I would like to use GPIO0_OUT. GPIO16 and GPIO17 are unavailable on PICO-D4.

The lan8720 needs a clock to do anything, not sure why there is no output on gpio0 for you

WiFive wrote: ↑

Tue Jun 18, 2019 8:19 pm

The lan8720 needs a clock to do anything, not sure why there is no output on gpio0 for you

Yes. I can confirm that on the same setup the config fails when I simply disable the 50MHz clock.


I checked again with an oscilloscope with GPIO0 open (disconnected from LAN8720) and i can see that ~50MHz clock does come on GPIO0 when setup with GPIO0_OUT but I noticed that the amplitude of the clock is very small (~0.2V peak to peak) while the same from the oscillator is nearly 2V peak to peak. Could this have anything to do with it?

Is there any way to increase the clock out amplitude as I suspect that to be the problem?