[Hackrf-dev] sample rate USB limitation

[Marc Pàmies Massip]

Oh, I thought that both columns should have the exact same values. Perfect then, I was worried about that. That's the output to the command that you asked:

39.8 MiB / 1.001 sec = 39.8 MiB/second
40.1 MiB / 1.001 sec = 40.1 MiB/second
40.1 MiB / 1.001 sec = 40.1 MiB/second
39.8 MiB / 1.001 sec = 39.8 MiB/second
40.1 MiB / 1.001 sec = 40.1 MiB/second
40.1 MiB / 1.001 sec = 40.1 MiB/second
39.8 MiB / 1.001 sec = 39.8 MiB/second
40.1 MiB / 1.001 sec = 40.1 MiB/second
40.1 MiB / 1.000 sec = 40.1 MiB/second
40.1 MiB / 1.000 sec = 40.1 MiB/second
39.8 MiB / 1.001 sec = 39.8 MiB/second
40.1 MiB / 1.001 sec = 40.1 MiB/second

It means that I could use such a high sample rate without problem?
For higher rates than 20 MHz it prints "couldn't transfer any bytes for one second."

Thanks again,

Marc.

On 01/02/2017 1:46:33, Dominic Spill <dominicgs at gmail.com> wrote:
On 31 January 2017 at 17:17, Marc Pàmies Massip <mpamies247 at gmail.com [mailto: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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