AW: AW: AW: Serial port interface on frame grabber

[James Cameron]

G'day vk_gst,

So GStreamer worked fine with a serial port that did not lose data?

If so, this is no longer a GStreamer problem per se.

Yes, I'm familiar with that class of wireless serial device.  Data can
be lost, and you have proved it is lost; the most common causes are;

- path fade,

- interfering transmissions from other devices on the shared
  frequency,

- badly configured flow control; if the firmware is configured to use
  XON/XOFF signalling from the host, it may drop all bytes 0x11 or
  0x13; so check for those bytes in the output you captured,

- missing flow control; the firmware has to buffer the data until it
  can be transmitted, and if the host continues to send data when the
  buffer is full, the data is lost; so you may have to add flow
  control lines if the host can take that,

You could work on these problems to improve the transmission test
until the shasum matches.

PPP might not help; I've not used it with lossy links for a very long
time, and I imagine it would become confused.

You could also find another RF serial module which includes delivery
guarantees.  Telemetry usually gives more recent data priority over
older data, and so doesn't need to guarantee delivery in-order.

On Wed, Jun 27, 2018 at 04:18:06AM -0700, vk_gst wrote:
> Hi James,
> 
> Thanks for the update. 
> 
> I have a 433MHz wireless Tx/Rx that connects over serial port. The idea was
> to try and use these wireless devices to stream video data on the PC from
> imx6. This is the device  here
> <https://www.unmannedtechshop.co.uk/100mw-ardupilot-unmanned-telemetry-kit-v2-433mhz/>   
> So this works on 3.3V TTL. 
> 
> With your previous test of sending and receiving the 1MB file, I performed
> it and found that only around 666KB were received at the receiver side. The
> binary comparison of the files revealed a number of random bytes being
> missed at the receiving side.
> 
> I performed the same test, with the usb-serial-serial-usb wired device (a
> small approx. 50cm cable we built long back) with 115200 baud and the file
> was received correctly at the receiver. The 'shasum' also matched in this
> case for the files. 
> 
> So, the H264 decoder at the PC side is just not receiving enough bytes to
> stream a video out of it. I do not know if using PPP here would be useful. I
> can try to use RTP over UDP over serial and then transmitting it wirelessly
> and see if it improves anything. But I am not sure. May be you can shed some
> light on this? 
> 
> 
> 
> 
> --
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-- 
James Cameron
http://quozl.netrek.org/