ESP8266 firmware implementing an I2C slave with spy, loopback and configurable clock stretch
This ESP8266 project implements an I2C slave with the following features
- spy: echos all traffic to UART
- loop-back: write bytes, read back
- clock stretch injector: can stretch any clock pulse
The firmware implements this as bit bang on two pins, using interrupts. Unfortunately, the ESP8266 has high interrupt latency: on 160MHz, the interrupt latency is ~4.3us. Note that slowest I2C has a clock of 100kHz, so interrupts come every 5us, which is tight. As a result it is recommened to run at e.g. 32kHz.
| REGISTER | ACCESS | MSB/LSB | DESCRIPTION |
|---|---|---|---|
| ENABLE | w/r | 00/01 | Number of transactions clock stretch is enabled |
| PULSE | w/r | 02/03 | The CLK pulse that is stretched (starts with 1) |
| US | w/r | 04/05 | Clock stretch time in us |
| QPULSE | r | 06/07 | Query: Number of CLK pulses in last transaction |
| QUS | r | 08-11 | Query: Number of us of the last transaction |
| RSVD | w/r | 12-15 | Reserved |
| MSG | w/r | 16-31 | Buffer foor loopback message |