Current frankenpcb is wired to do MIDI via GPIO13 / GPIO15. Which is still UART0, but after the initialization code calls `Serial.swap()`. Extra modboard is a buffer from a quad NAND for MIDI OUT from GPIO15. GPIO15 needs to be pulled down for esp8266 to boot correctly, but the MIDI OUT circuit pulls it up without the buffer.

This whole set-up is a lot "quieter" on start up. But it still generates a single pulse on MIDI OUT, which gets interpreted as `B0 00 00` by my USB MIDI adapter.