[Hackrf-dev] sample rate USB limitation

[Dominic Spill]

On 31 January 2017 at 17:17, Marc Pàmies Massip <mpamies247 at gmail.com>
wrote:
>
> I am using a HackRF with my laptop (HP Spectre from 2016), but I am not
sure if its USB ports are good enough for this device. You can find
attached the output of "hackrf_transfer -r NUL -s 8000000", and as you can
see the values from the first column are not always the same as in the
second column. I was using the minimum sample rate recommended for the
HackRF (8 MHz), so does it mean that I should use another computer to
obtain reliable results? Is there a way to fix this without changing the
computer or I should just work with sample rates under the minimum
recommended?

This output looks good to me, at 8MHz we expect a pair of bytes 8 million
times per second, which matches the data rate you are seeing - 16MB/s.
Could you try the same with "hackrf_transfer -r /dev/null -s 20000000" to
see what the maximum throughput you can achieve is?  I would expect you to
get an average of 40MB/s with that.  You can even try pushing it higher
than 20MHz, but you will approach the limit of the USB 2.0 connection very
quickly and the throughput will drop.

> PD: I don't know if it has anything to do with this, but according to the
output of "hackrf_info" my firmware version is 2014.08.1. Should I upgrade
it or it's not necessary?

Yes, it is always recommended to run the latest release host code and
firmware.  The current version is 2015.07.2.

Thanks,
  Dominic
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