Archive for category: By Ridge Solutions

Update: I have written a simple Fire-And-Forget wrapper class for sending datagrams via UDP can be found here. It handles simple transmission use cases while hiding the (sometimes confusing) boost::asio details. However, if you are interested in the details then read on!

Boost.ASIO is great but if you don’t use it everyday it can be hard to remember how to use it to do even the simplest of things. I have included below a sample of simply sending a packet via UDP (ipv4), see the function called send_message(), this example code aims to be as minimal as it can be:

Those spouting software engineering dogma will often tell you to steer well clear of UDP for the usual, well understood reasons, but for a certain type of application where very low latency is important, it just can’t be beat!!

#include 
#include 
using namespace boost::asio;
//
// Send a string via UDP to the specified destination
// ip addresss at the specified port (point-to-point
// not broadcast)
//
bool send_udp_message(const std::string& message, const std::string& destination_ip,
						const unsigned short port) {
	io_service io_service;
	ip::udp::socket socket(io_service);
	// Create the remote endpoint using the destination ip address and
	// the target port number.  This is not a broadcast
	auto remote = ip::udp::endpoint(ip::address::from_string(destination_ip), port);
	try {
	
		// Open the socket, socket's destructor will
		// automatically close it.
		socket.open(boost::asio::ip::udp::v4());
		// And send the string... (synchronous / blocking)
		socket.send_to(buffer(message), remote);
	
	} catch (const boost::system::system_error& ex) {
		// Exception thrown!
		// Examine ex.code() and ex.what() to see what went wrong!
		return false;
	}
	return true;
}

This is the bare-bones code, no error reporting etc. Also it won’t broadcast, to allow for broadcast you need to include the following two lines and supply a broadcast ip address when calling the function. Be careful if broadcasting a lot of data as it can really overload & mess-up network equipment!

socket_base::broadcast option(true);
socket.set_option(option);

echo "my packet data" > /dev/ttyS0

cat /dev/ttyS0

# Run cat in the background
cat /dev/ttyS0&
# Send the command, cat should print the response
echo "my packet data" > /dev/ttyS0

(read -n60 -t20 RESP < /dev/ttyS0; echo $RESP)&
echo "my packet data" > /dev/ttyS0

#!/bin/sh
#
# Send a packet to the specified serial port
# and wait for, and output the response, it is assumed
# that the response will end with an EOL character.
#
# usage: send_tty.sh <data-to-send> <port>
#
# [backgound] Wait for, and read a line from the serial port into RESP,
# max 128 characters, timeout=10s, then output $RESP
#
# (c) 2019 Kevin Godden
#
(read -n128 -t10 RESP < $2; echo $RESP)&
# Hack - use read to pause for 200ms to give previous
# command a chance to get started..
read -p "" -t 0.2
# Send command
printf "$1\r" > $2
# Wait for background read to complete
wait

./send_tty.sh "my-command" /dev/ttyPS0./send_tty.sh "my-command" /dev/ttyPS0

ExifTool can be used to output a specific Exif MakerNote from your images’ metadata by using the following command:

exiftool -u -Unknown_0x0013 image.jpg

This will output makernote Id 0x13, however if the makernote that you are interested is long, then ExifTool may truncate it and output only the start with […] at the end!

Unknown 0x0013                  : {"distortion":{"factory":{"version":"1.0","medium":"air[...]

To have ExifTool output the full makernote, use the -b (binary) option like this:

exiftool -u -b -Unknown_0x0013 image.jpg

As a software engineer (rather than an NTP guru), I find that configuring and debugging an NTP setup can be quite challenging, it is (by its nature) a difficult subject, and a lot of the info out there is quite dense and hard to parse, so I was presently surprised to come across this nice article, called ‘Real Life NTP’ which gives a good overview and describes the use of ntpq -p etc.

https://pthree.org/2013/11/05/real-life-ntp/

Thanks Aaron!