Re: Building a custom UART interface for gpsd

[Gary E. Miller]

Yo Aleks!

On Thu, 12 Sep 2024 17:36:45 +0000
Aleks Pop Stefanija <alekspop@mit.edu> wrote:

> I was hoping someone could direct me to more information about the
> "Magic Macx mod" referenced at the bottom of this document:
> https://gpsd.gitlab.io/gpsd/hardware.html

Nothing magic about it.  Just opening up the GNSS receiver and
connecting the PPS line to  DCD.

> I am currently trying to build a custom UART interface for gpsd using
> a ublox ZED-F9T GNSS receiver and Raspberry Pi RP2040.

Something wrong with the standard serial interface?

> The PPS output
> from the ublox is tied directly to the DCD# line of a custom USB UART
> interface. The TX/RX lines of this interface actually come from the
> RP2040.

Lost me.  If you use the TX/RX lines from the Pi, what exactly are
you adding?  Got a diagram of your "custom  UART"?

BTW, the TX/RX lines on the on the Pi are nothing close to a UART.

> This is so the RP2040 can package NMEA messages from the
> ublox (via the ublox UART1 serial port) together with measurements
> from auxiliary instruments (i.e., a magnetometer and IMU).

Odd combination.  Th F9T is designed for fixed use, so no measurement
for the IMU to measure.

> The RP2040
> is running a CircuitPy and is able to read serial messages from the
> ublox UART1 port. Now comes the part of relaying those messages over
> the custom UART interface in a format, together with PPS, that can be
> interpreted by gpsd.

Lost me, how do you intend to multiplex?  How would the Linux kernel
understand your PPS??

> It seems to me like the Magic Macx mod could be
> related to this problem.

Macx is a mod to a crippled receiver to restore normal behavior.  Nothing
at all like what I think you are describing.

RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        gem@rellim.com  Tel:+1 541 382 8588

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