SoftwareWire
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Testato
Problem with servo's
Hi, I am a happy user of your library. Yesterday I ran into a problem however. I was using a software I2C on pins D12 (SDA) en D13 (SCL). This works fine. When I attached a group of 6 servo's (pin D3-D5-D6-D9-D10-D11)) to the controller the problem occurred. The servo's on D9, D10 and D11) connected to PortB (same Port as SDA-D12 and SCL-D13) these servo's started oscillating. This also happens when the servo-objects are not written to.
When I moved the software I2C to PortC (A0-SDA and A1-SCL) the problem was gone.
Does the timing of SoftwareWire interfere with the servo timing?
Kind Regards, Willem Braat (Netherlands)
Yes, it does interfere. Thank you for reporting this issue and for your clear explanation.
It is the same issue as issue https://github.com/Testato/SoftwareWire/issues/5
The Servo library uses one timer with one interrupt. In the interrupt routine the PWM signals are written to the pins. To do that, the interrupt must run at a high rate. The SoftwareWire library reads a register, changes a bit, and writes the register back. That is not safe.
The OneWire/OneWire.cpp library uses noInterrupt() and interrupt() every time a register is changed. We have to add that as well.
Can you use a different port to avoid it?
Thanks you for the quick response. When I moved the software I2C to PortC (A0-SDA and A1-SCL) the problem was solved!
Regards, Willem
It is not often that one uses all 6 PWM ports. For this design it was necessary. So, the workaround is quite simple: don't run SoftwareWire on a port that drives a servo... :-) Willem