SD card example in 4 line mode

[ESP_igrr]

Good to know that the issue has been resolved. Once you transition to the design on a PCB, you may also double the speed by going from 20MHz to 40MHz clock, if you haven't already (https://docs.espressif.com/projects/esp ... -frequency) Increasing buffer size (especially for write operations), and bypassing buffering at stdio level (using read(fileno(f),...)) can help increase the speed even further.