Adafruit Ultimate GPS Breakout and Pi 3

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meadowvole
 
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Adafruit Ultimate GPS Breakout and Pi 3

Post by meadowvole »

Hi, I noticed the Adafruit Ultimate GPS HAT for Raspberry Pi A+/B+/Pi 2 - Mini Kit is not currently compatible with the Raspberry Pi 3 but I was wondering if the Adafruit Ultimate GPS Breakout - 66 channel w/10 Hz updates - Version 3 is compatible with Pi 3 since it doesn't say anything either way in its store page description. They seem to use the same basic module.

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adafruit_support_mike
 
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Re: Adafruit Ultimate GPS Breakout and Pi 3

Post by adafruit_support_mike »

The GPS breakout will work with a Pi3 if you connect it through a USB-to-Serial adapter. Getting it to work when connected to the Pi3's GPIO pins is more of a problem.

The trouble traces back to how the microprocessor's UARTs are assigned. Non-Pi3 RasPis route uart0 to the GPIO header because it's stable and fairly easy to work with. The Pi3 assigns uart0 to the onboard BLE hardware for exactly the same reason, and assigns uart1 to the GPIO pins.

The problem is that uart1's clock is derived from the system clock, and the Pi3's system clock changes speeds when the processing load changes.. faster when there's a lot of data to cruch so the system is more responsive, slower when the CPUs are mostly idle to reduce power consumption.

Every time that happens, the baudrate on uart1 changes. That messes up any connection that may have existed, and generally makes the GPIO serial pins harder to work with.

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meadowvole
 
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Re: Adafruit Ultimate GPS Breakout and Pi 3

Post by meadowvole »

Thanks for the thorough reply. I see now why the hat doesn't work with pi3. I'll give it a try with the usb/serial adapter.

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