Re: [Paparazzi-devel] Futaba SBUS through R/C connector on Umarim

[Gautier Hattenberger]

Hi,

Le 14/06/2015 15:00, Joseph Muhlhausen a écrit :

Hi Gautier Thanks this is very useful. I had not thought about the interrupts.

I did a little bit more research:

- There is a SBUS to CPPM from Frsky which I tested. It works well but it becomes an anagogic signal and the SBUS SIGNAL_LOST bit is not carried through.

It all depends on the behavior of the converter when the signal is lost. If it keep sending a "failsafe" value, you'll not be able to tell if it is lost, but if the signal becomes null, you'll have the info.

A hack we did some time ago for lpc21 is to use the led signal of the receiver (if the color is changed/tuned off when the signal is lost) and put this to a GPIO input. Then you need to define some stuff to turn this into RC_LOST signal.

See sw/airborne/arch/lpc21/subsystems/radio_control/ppm_arch.h:54
And for the airframe (for pin P0.17):

    <subsystem name="radio_control" type="ppm">
      <define name="USE_PPM_RSSI_GPIO"/>
      <define name="PPM_RSSI_IOPIN" value="IO0PIN"/>
      <define name="PPM_RSSI_PIN" value="17"/>
      <define name="PPM_RSSI_VALID_LEVEL" value="0"/>
    </subsystem>

- I can use a Lisa M2 (easier to find) with an inverter.

I guess it should work, but I don't use Lisa boards

- I could write a SBUS serial driver for I2C? (I am not sure about this one).

I don't think it works

How difficult would it be to write and SPI driver for xbee?

I never tried, probably a bit annoying....


Gautier

Joseph

On Sun, Jun 14, 2015 at 4:23 AM, Gautier Hattenberger <address@hidden> wrote:

Hi,

If plan to use an UART input for SBUS, you'll also need to invert the signal (the SBUS signal is not a standard serial: different idle level, unusual baud rate), and as you figured it, there is only two UART on Umarim board. An no easy solution:
- fix the gps-i2c driver if you are using an ublox gps.
- implement gpio based (probably better use the input capture pin (PPM)) to read the signal by hand (benefit is that you don't need the inverter, but it will generate a lot of interrupts).
- write an spi driver for XBee.
- use an Apogee board (unfortunately a bit difficult to find these days... ).

Gautier

Le 13/06/2015 23:58, Joseph Muhlhausen a écrit :

According to the data sheet for NXP LPC2148 there are only two UART available. I wonder if there is a way to connect it via SPI or IC2.

On Thu, Jun 11, 2015 at 2:09 PM, Joseph Muhlhausen <address@hidden> wrote:

I am switching to a futaba sbus system and it looks like both UART port are occupied by an xbee and a GPS on Umarim lite 2.0. 

Can I read the sbus signal via the PPM pin on Umarim?

Or can I use a GPIO pin instead?

Thanks,

Joseph

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