Colibri iMX6ULL

Description: Due to the Microchip KSZ8041NL Ethernet PHY errata, the Ethernet can become unusable after exiting the power save mode. The Ethernet PHY is powering down the PLL during the software power down, which can create problems. The issues only appear under certain circumstances and in certain temperature ranges. The issue cannot be reproduced with all modules.

Workaround: Microchip is recommending not using the software power-down of the Ethernet PHY. This means the Ethernet PHY should be left running even in the module's power save (suspend) mode. However, this increases the module's power consumption in the power save state.

Description: The Microchip KSZ8041 Ethernet PHY has an errata: https://ww1.microchip.com/downloads/en/DeviceDoc/80000700A.pdf. According to the second item in the document, a small percentage (less than 1%) of the devices can potentially fail to properly read the strapping pins and set the intended configuration if the 3.3V supply rail rises too fast. On the Colibri iMX6ULL SoM, the 3.3V power rail for the Ethernet rises faster than the required 250us. Therefore, on rare occasions, a small amount of Colibri iMX6ULL SoMs may fail to communicate with the Ethernet PHY after power-up. If the strapping of the PHY configuration fails, the system cannot communicate with the PHY over the MDIO interface. The Ethernet port is not working in this case. According to our tests, the issue mainly appears on the affected modules if the power is enabled at extremely low temperatures (below -30°C). The pull-up resistors of the Ethernet LEDs on the carrier board can backfeed to the 3.3V Ethernet power rail on the module. This backfeeding actually reduces the risk of strapping failures.

Workaround: There is currently no permanent workaround. If the Ethernet PHY is not accessible, try to power cycle the Ethernet PHY or the complete Colibri SoM. Disabling the RMII clock turns off the Ethernet power rails. Try waiting at least 1 second before reenabling the RMII clock and initializing the Ethernet PHY.