However, in the case of the Powershot N (as I stated), my tests indicate that the decision about whether to start when USB power is applied or not is controlled by the camera firmware rather than a seperate charge controller chip. CHDK loads and runs (briefly) before something in the firmware decides there is nothing intelligent connected to the D+ & D- pins. This is different that detecting some resistor combination (which my PC USB port does not have BTW). I suppose it's possible that the firmware gets a USB status from a small charger chip but my conclusion remains the same - getting around this requires modifying the boot.c code rather than hardware.My conclusions only ... it would not be the first time I have been wrong.
Quote from: srsa_4c on 29 / September / 2014, 17:37:20The PowerShot N also wakes up on USB connection. Time for some more experiments.
The PowerShot N also wakes up on USB connection.
I don't know how you are concluding that enumeration is taking place in firmware but it doesn't matter how the voltages are supplied or whether enumeration takes place in hardware or in firmware.
All that's important is supplying the correct data voltages. What do you mean by "nothing intelligent connected to the D+ & D- pins"? What intelligence does a computer's USB port supply when it is idly connected to a device like this, other than fixed voltages? Did you measure them and then try applying the voltages you measured to the appropriate data lines? That's all you need to do.
So you still haven't measured the D+/D- voltages your computer is supplying?
What happens when you connect the camera to your PC? Does a dialog pop up? If so, then there is some kind of data exchange going on.
If not, then that is a good case for simple voltage detection going on.
I just remembered that you said that this camera's battery is charged via the USB port so all the more reason to believe it is just looking for voltages since that is the rule rather than the exception for USB charging. Apparently this camera has no fall-back default charging level if no voltages are present on data lines.
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