Hey Sam,
I could get it done with the example code you refered to. Thank you very
much!
Knut
Am 05.03.2020 um 17:39 schrieb Sam Reiter:
Hey Knut,
Reading a GPIO line requires that the GPIO state be sent back to the
host, processed, and then acted upon (in your case, sending a stream
command to the radio). There is going to be a good amount of latency
and jitter built into this.
The alternative, which I would strongly recommend, would be to have
the USRP source the trigger. This can be set up really easily with ATR
- an FPGA functionality that coordinates GPIO states with radio TX/RX
states. I'd expect your TX start and GPIO state change to be
coincident on the order of nanoseconds. Checkout the gpio.cpp shipping
example for more info:
https://github.com/EttusResearch/uhd/blob/UHD-3.15.LTS/host/examples/gpio.cpp
If you need to differ the time between TX beginning and GPIO changing
state, you can use timed commands on both and force the offset.
Sam
On Thu, Mar 5, 2020 at 9:02 AM Knut Stolzenberg via USRP-users
<[email protected] <mailto:[email protected]>> wrote:
Hello,
I have set up a trigger for my X310 using the Pin 2 of the GPIO Front
Panel. The Trigger is a TTL signal fed to the Pin. But we
experience a
jitter of ~100µs between the Trigger and the SDR starting to send
data.Is it possible to reduce this latency/ jittering to <10µs. If
not
is it possible to use e.g. Pin 6 as a trigger output, which
signalises
when the SDR starts to send data? How would I implement this in the
code? This would be interesting to me, since I could then
synchronise my
experiment to the SDR and not vice versa.
The code we use for setting up the trigger is pretty similar to
what is
on the ettus knowledge base. The important bits are these:
...
...
...
//Declarate Pin 2 as Trigger Input -> this is used for the
triggered mode
#define MAN_GPIO_MASK (1 << 2)
#define AMP_GPIO_MASK (1 << 6)
#define ATR_MASKS (AMP_GPIO_MASK | MAN_GPIO_MASK)
// set up our values for ATR control: 1 for ATR, 0 for manual
#define ATR_CONTROL (AMP_GPIO_MASK & ~MAN_GPIO_MASK)
// set up the GPIO directions: 1 for output, 0 for input
#define GPIO_DDR (AMP_GPIO_MASK & ~MAN_GPIO_MASK)
....
....
....
usrp->set_gpio_attr("FP0", "CTRL", 0, ATR_MASKS);
usrp->set_gpio_attr("FP0", "DDR", 0, ATR_MASKS);
while (true)
if (0 != usrp->get_gpio_attr("FP0", "READBACK", 0)) {
/*here should be Pin 6 or "output trigger" high*/
for (int i = 0; i < line; i++) { /*send data
to the
SDR*/
tx_stream->send(
buff_ptrs[i], spb, md
);
}
/*here should be Pin 6 or "output trigger" low
}
}
Sincerely,
Knut
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