ESP8266: I2C transmission rate stays at 100kHz

[KarateBrot]

Adafruit_SSD1306.cpp, line 461 - 464

#ifdef TWBR
  uint8_t twbrbackup = TWBR;
  TWBR = 12; // upgrade to 400KHz!
#endif

When using ESP boards these lines seem to get ignored so the I2C rate stays at 100 kHz.

The problem here is that Adafruit_SSD1306::display takes way too long to transmit data with 100 kHz and therefore yielding only ~10 fps on my display which is way too slow. You can actually see every frame building up. 🐌

I tried this on a WeMos D1 Mini (4MB) and on a NodeMCU.

---

• How I fixed it

In void setup(){} I inserted Wire.setClock(400000L); to successfully get 400 kHz on my ESP boards and ~30 fps on my display.

void setup()
{
  Wire.setClock(400000L);
}

• Possible solution

Add code to Adafruit_SSD1306.cpp, line 465:

#ifdef TWBR
  uint8_t twbrbackup = TWBR;
  TWBR = 12; // upgrade to 400KHz!
#endif
 
#ifdef ESP8266
  Wire.setClock(400000L);
#endif

---

Additionally:

In this case an 800 kHz transmission rate seems to be the maximum. By calling Wire.setClock(800000L); ~60 fps can be achieved on SSD1306 OLEDs using an ESP8266. That's nearly a sixfold increase in drawing speed! compared to what's possible out of the box right now.

[guru-florida]

As suggested above, adding this to Adafruit_SSD1306 worked for me. My drawing went from 112ms to 30ms...9fps to 30fps! Thanks @KarateBrot !! Now my ECG heart monitor is graphing my heartbeat smoothly!

#ifdef ESP8266
  Wire.setClock(800000L);
#endif

Trying to set in setup() didnt work. The Adafruit lib (or Wire) resets it back to 100k.

[KarateBrot]

Trying to set in setup() didnt work. The Adafruit lib (or Wire) resets it back to 100k.

It only worked for me if I put the function call at the end of the Setup() routine.
This way Wire.setClock() ultimately overrides the Wire settings no matter what.

[PaintYourDragon]

Library v1.2 incorporates faster I2C transfers.