I have a project that runs on a custom LPC1768 board. The project uses Ethernet (with lwip in NO_SYS=1 mode) and UART for debug.
It works well many times. However I noticed a strange relation between UART and Ethernet.
Normally I can communicate with a server (MQTT over TLS). I can see frames/packets out and in and the communication is ok.
When I add some debug output in LPC Ethernet driver (for example in low_level_output() in lpc17xx_40xx_emac.c), Ethernet works differently. It seems some incoming frames that are normally received, aren't received now.
I know it's a very big question, however what could be the relation between UART and Ethernet?