In case anyone is interested, I got this to work with code similar to the
following. Note that “usrp_alias” must be fetched from an already constructed
usrp_sink object, for instance using “self.usrp.alias()” in a Python-based
flowgraph.
// gr-my-oot/include/my-oot/clock_manager.h
class MY_OOT_API clock_manager : virtual public gr::block
{
…
public:
static sptr make(const std::string &usrp_alias);
…
}
// gr-my-oot/lib/clock_manager_impl.h
#include <gnuradio/uhd/usrp_sink.h>
class clock_manager_impl : public clock_manager
{
private:
gr::uhd::usrp_sink::sptr d_usrp;
…
}
// gr-my-oot/lib/clock_manager_impl.cc
#include <gnuradio/block_registry.h>
#include <boost/pointer_cast.hpp>
#include <pmt/pmt.h>
clock_manager_impl::clock_manager_impl(const std::string &usrp_alias)
: gr::block(“clock_manager”, …)
{
basic_block_sptr blk;
std::vector<std::string> sensors;
try {
blk = global_block_registry.block_lookup(pmt::intern(usrp_alias));
d_usrp = boost::dynamic_pointer_cast<gr::uhd::usrp_sink>(blk);
} catch(const std::runtime_error& err) {
std::cerr << “Unable to find USRP instance in block registry.” <<
std::endl;
}
if(d_usrp)
{
try {
std::vector<std::string> sensors;
bool found_gpsdo = false;
sensors = d_usrp->get_mboard_sensor_names(0);
for(std::vector<std::string>::const_iterator it = sensors.begin();
it != sensors.end(); it++) {
if(*it == “gps_locked”) {
found_gps = true;
break;
}
}
if(!found_gpsdo)
std::cerr << "USRP device does not have a GPSDO installed." <<
std::endl;
} catch(const std::runtime_error &err) {
std::cerr << “Unable to query a valid USRP device.” << std::endl;
}
} else {
std::cerr << “USRP shared pointer is not valid.” << std::endl;
}
}
From: [email protected]
[mailto:[email protected]] On Behalf
Of Martin Braun
Sent: Friday, January 29, 2016 5:35 AM
To: Marcus Müller <[email protected]>
Cc: [email protected]
Subject: Re: [Discuss-gnuradio] USRP control thread in GR block - how do I pass
a USRP sptr?
Marcus is right, but your approach should technically work as well. I rarely
get C++ polymorphisms and pointers right at first go, but using
dynamic_pointer_cast should work and be safe - ish.
M
On 29 Jan 2016 10:28, "Marcus Müller"
<[email protected]<mailto:[email protected]>> wrote:
Sorry, I just got a friendly reminder that this is a bad idea in many ways; the
recommended way of getting a handle to your USRP block is passing the block
alias around and looking it up in the block registry; that's why we have it
anyway.
Make sure the result of the lookup is valid!
Best regards,
Marcus
Am 29. Januar 2016 09:13:42 MEZ, schrieb "Marcus Müller"
<[email protected]<mailto:[email protected]>>:
Hi Sean,
it's been a while since I did that, but I think that "smart_ptr<A> cannot be
casted to smart_ptr<B>" can be remedied using Boost's pointer_cast[1].
Hope that gives you a start.
Best regards,
Marcus
[1] http://www.boost.org/doc/libs/1_60_0/libs/smart_ptr/pointer_cast.html
On 01/28/2016 08:34 PM, Nowlan, Sean wrote:
I have a USRP with a GPSDO. I am working on a block that will poll a USRP for
PPS changes in an attempt to adjust for clock offset between host and USRP.
Assume I have explicitly set the USRP time-of-day correctly to UTC using PPS
and a set_time_next_pps_call, and GPS is locked.
I would like to pass a USRP sink (or source) shared pointer to this block. It
will have its own internal thread that will loop waiting for PPS edge
transitions, polling with get_time_now, and then measuring offset between
PC/system clock and USRP clock.
Following guidance from a mailing list thread [1], I attempted to pass a
usrp_sink shared pointer as a basic_block_sptr and then dynamic_cast it in the
block xtor. Here’s the error I get:
clock_manager_impl.cc: In constructor
‘gr::mymodule::clock_manager_impl::clock_manager_impl(gr::basic_block_sptr,
double, const string&)’:
clock_manager_impl.cc:50:59: error: cannot dynamic_cast ‘usrp’ (of type
‘gr::basic_block_sptr {aka class boost::shared_ptr<gr::basic_block>}’) to type
‘gr::uhd::usrp_sink::sptr {aka class boost::shared_ptr<gr::uhd::usrp_sink>}’
(target is not pointer or reference)
d_usrp(dynamic_cast<gr::uhd::usrp_sink::sptr>(usrp)),
Any advice on the best way to do this? Is my approach sane?
Thanks,
Sean
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