Hi Rabeeh,
On 05/04/2015 03:35 PM, Rabeeh Khoury wrote:
On 05/04/2015 07:18 AM, Nikolay Dimitrov wrote:
Hi Fabio,
On 05/04/2015 06:30 AM, Fabio Estevam wrote:
From: Fabio Estevam fabio.estevam@freescale.com
mx6cuboxi sometimes fails to recognize the Ethernet PHY:
Net: Phy 0 not found
The explanation comes from a patch from Rabeeh:
"The LED_ACT pin on the carrier-one boards had a pull down that forces the phy address to 0x0; where on CuBox-i and the production HummingBoard that pin is connected directly to LED that depending on the pull down strength of the LED it might be sampled as '0' or '1' thus the phy address might appear as either address 0x0 or 0x4."
There's no such thing as "LED pull-down". The forward voltage drop of a LED is between 1.65V (red low-power LEDs) to 2.1V (green LEDs) to even more for blue LEDs. Even the lowest Vf doesn't qualify as logic "0" for LVCMOS33, which is around 1V max (Vil). The LED just can't pull-down the voltage level low enough.
This is AR8035 implementation; in reset stage the LED pin is configured as input, and pull up/down does matter. In this case it configures the PHY address.
After reset is deasserted the same LED pin becomes output and then according to the previous pull/up it should be active high/low (i.e. driver or sink).
I know this. This is why I said that the pin is floating and the R+LED can't define a proper logic level during configuration bootstrapping. In such situations there should be an external pull-up/pull-down to make sure things work properly.
Regards, Nikolay