Notes, SPI - mhightower83/Arduino-ESP8266-misc GitHub Wiki

SPI Self Study References

SPI RTOS API Reference

SPI Flash I was interested in the "Memory Type" meaning in the JEDEC ID. Unresolved, maybe manufacturer depended. also esp-edf comment. (I could be wrong on this.) I think the device ID field is manufacturer-dependent. However, Devices that support Serial Flash Discoverable Parameter (SFDP), offer the ability to get the details needed in a standard way.

d.av.id.au blog on Wayback Link to a curated version of decommissioned website d.av.id.au's blog post on ESP8266 SPI Registers, He has some good low-level ESP8266 register SPI info also read comments in his about section via Wayback. His signal traces show really high Ringing on the SPI Bus signals. He attributes it to breadboard wiring; however, I had these as well until I added series resistors(not really a termination issue the wire length was too short). I would love to ask him about this; however, he has not accessed Github in 6 years and his blog has gone inactive. Use Wayback to access the post. Strangely, his YouTube account is still active.