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ms-iot / BusProviders

Repository for Windows IoT Core Bus Provider Libraries
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Pi 3 - DmapSupport GetControllerBaseAddress for BCM2844 does not find device??? #44

Closed ghost closed 7 years ago

ghost commented 7 years ago

I've been trying to enable either PWM0 or PWM1 using the proper alternate function calls to the relevant register on the BCM2835. I think I have the pin configured properly but now I need to enable the PWM in the proper register in the BCM2844 chip. I can see the "#define pi2PwmDeviceName" in the DmapSupport.h file but when I try to use the "GetControllerBaseAddress" function using the PWM device name it comes back blank. I've looked in the dmap.inf file on the Pi and I see "%dmap.DeviceDesc%=dmap_Device,*MSFT8001,ACPI\BCM2841,ACPI\BCM2845,ACPI\BCM2838,ACPI\BCM2839" but there's no BCM2844? Was this done on purpose? Can anyone supply any help so I can write to that chips register to get any PWN working?

The software driven PWM isn't dependable enough for my setup...

Help Please (and thanks)

Jim

IoTGirl commented 7 years ago

Hi jamoeder,

I reached out to a member of the IoT Core Team and have the following answer for you:

Is there any reason he isn’t using the lightning driver rather than trying to do this directly to the HW? He says SW PWM isn’t reliable enough, and I agree, but Lightning is HW PWM.

Please try the Lightning solution as it should meet your needs. Sincerely, IoTGirl

ghost commented 7 years ago

Thanks so much for the reply. I really appreciate it.

The HW PWM in the Lightning solution is for a breakout board (PCA9685). Although this is not the preferred solution it will work but I have to buy new hardware which is something I'd like to avoid if possible. Did they run out of time before the current IOT release or was there a specific limitation that stopped them from enabling the BCM2844 registers? Is there any chance you can post the DMAP driver so it can be modified to add support for the chip?

Again, Thanks for the response thus far.

Jim

IoTGirl commented 7 years ago

Hi Jim,

I have the following responses for you

So it’s mostly due to extra HW then… Jesse provides background here https://github.com/ms-iot/lightning/issues/35#issuecomment-218862919 but basically it is because of the underlying design of the Pi PWM controller. While I would still agree with Jesse, if he wants to look through the dmap code it is located here https://github.com/ms-iot/lightning

The hardware PWM on the pi is useful for tone generation and fan speed control, but not servos, steppers or RC signaling. This makes it not compatible with most arduino projects or expectations, so we decided to optimize for an off SOC solution. It could be added, sure, but I worry about it being a bug farm. The DMAP driver isn't need, as the lightning code which is open source could be modified to support it as PWM is same data page which covers gpio

So it was a conscious decision not to enable as the HW would not meet expected performance. Although Microsoft is not going to enable it, you can look at the code yourself and if you are realistic about the perf you could enable it for your own purposes.

I hope that helps! IoTGirl

ghost commented 7 years ago

Great Answer! Thank you (and Jesse) very much for the clarification.

So... For fun and profit, what are the chances you can post the DMAP drivers so I can enable BCM2844 chip and allow access to the PWM registers? If I can get it to work I'd be happy to share?