unfortunately the suggestions above do not work for esp-idf version 4.
Is anyone able to suggest code to run a softAP http server in v4.1?
or perhaps able to port the code?

sorry if this is a noob question :

ESP-ADF says it is open source, yet, I cannot find the implementation of the function esp_equalizer_process(), only its definition in a header file.
Are there parts of the ADF for which the source is not available?

I am happy to report it was indeed a short. The culprit was the sd->eMMC adapter card. The traces are very close together and short where they contact the micro->sd adapter. There is a sweet spot that prevents the short but keeps the connections intact. I am not sure why I didn't think to check for ...

Does cross-talk like this between signal lines point at the same signal integrity issues as before, in your experience? Or does this look like a driver issue?
thanks!

it appears that BIT3 and BIT4 are OR'd,
likewise BIT7 and BIT8 are OR'd

the errors are always in the 3rd,4th,7th or 8th bit ... does this again point at signal integrity on 2 of the 4 lines?

I use 1-line mode to write numbers from 0-255 to the card. I use 4-line mode to read them back, using this code: #define BYTE_TO_BINARY(byte) \ (byte & 0x80 ? '1' : '0'), \ (byte & 0x40 ? '1' : '0'), \ (byte & 0x20 ? '1' : '0'), \ (byte & 0x10 ? '1' : '0'), \ (byte & 0x08 ? '1' : '0'), \ (byte & 0x0...

I will try those ideas out.
Thank you for your help, please let me know your findings!

In the meantime do you have a list of known compatible eMMC module/breakout/adapter boards?

these are the connections I am using, same as suggested in the sd_card example read_me, all with 10k pull-ups.

GPIO14 -> CLK
GPIO15 -> CMD
GPIO2 -> D0
GPIO4 -> D1
GPIO12 -> D2
GPIO13 -> D3

here is an image of the circuit and adapters I am using.