I2C hang with very slow I2C slave (pic12f1840@500khz)

[miky2k]

----------------------------- Remove above -----------------------------

Basic Infos

Hardware

Hardware: ESP-07
Core Version: 2.2.0

Description

On very slow device i2c hang SDA low and give strange results 01111001 instead 00111100 .

Settings in IDE

Module: Generic ESP8266 Module
Flash Size: 512K/64K
CPU Frequency: 80Mhz
Flash Mode: qio
Flash Frequency: 40Mhz?
Upload Using: SERIAL?
Reset Method: ck

Sketch

Wire.begin(12,13); //I2C pin
Wire.setClockStretchLimit(2000);

In my software(l is not important) :
Wire.beginTransmission(Addr);
Wire.write(0b00111100);
Serial.println("I2C write---"+String(l));
Serial.println(Wire.endTransmission(1));

Serial Output:

I2C write---4
3

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[me-no-dev]

any particular reason why your slave does not release SDA?

[miky2k]

I disconnect physically only sda from device but bus remain low(esp8266 take bus low),
i know that my device may have bad beauvoir but hang sda is quite strange from a master.

Ok the problem is quite complex (or simple now i found it).
Semms that some libraries initialize Wire with Wire.begin() in costructor resetting clockStretch value ,it is difficult to debug because twi_byte_write not report any protocol error (only ack!).
My propose is to accept only greater timeout than current in twi_setClockStretchLimit ,
not difficult to implement i suppose .
And add -1 to twi_byte_write if protocol error occur (stretch limit occur).

[devyte]

@igrr this has milestone 2.4.0. However, I don't fully understand the issue, let alone what needs to be fixed in Wire.
Is the issue still relevant?

[miky2k]

If you need different clock stretch timings on devices is relevant!

Ad is very simple to implement as i described.

[enjoyneering]

check this - https://github.com/enjoyneering/ESP8266-I2C-Driver

[d-a-v]

For reference (link)
I will make a PR for that

unless @enjoyneering you wish to make it with your changes ?