How to extract the elapsed time from a timer object in MATLAB? - matlab

Question

Is there any way to extract the elapsed time from the beginning of each period from a timer object in MATLAB?
Say we have a timer object like this:
t=timer('ExecutionMode', 'fixedRate', ...
'Period', 15, ...
'TimerFcn',#(x,y)disp('Hello World!'))

Answer 1

The y contains the absolute timestamp. Store it when the timer is stated and take the difference:
function my_callback(m,x,y)
persistent starttime
switch m
case 'start'
starttime=y.Data.time;
case 'timer'
disp(datenum(y.Data.time-starttime)*24*60*60);
otherwise
error('unknown argument');
end
end
With a timer:
t=timer('ExecutionMode', 'fixedRate','Period', 15,'StartFcn',#(x,y)my_callback('start',x,y),'TimerFcn',#(x,y)my_callback('timer',x,y))
start(t)
Alternative solution using userdata:
t=timer('ExecutionMode', 'fixedRate','Period', 15,'StartFcn',#(x,y)set(x,'UserData',y.Data.time),'TimerFcn',#(x,y)disp(datenum(y.Data.time-get(x,'UserData'))*24*60*60))

Answer 2

Approach using tic, toc and 'UserData'
There is no direct method on the timer-object to read the elapsed time since its last call. It is possible to use a construct with tic and toc to achieve what you want.
The generic field 'UserData' can be used to add user-data to the timer object. We can write this value with set() and read it with get(). So we set this value with tic in the callback-function and get it back later to compute the time difference using toc.
More specifically, here is the callback-function:
function timerCallback(timerObj,event) %#ok<INUSD>
disp('Hello World!');
set(timerObj,'UserData',tic);
Now we can write a wrapper-function to get the elapsed time:
function retval = getElapsedTime(timerObj)
retval = toc(get(timerObj,'UserData'));
Example usage of proposed approach
To see if this approach works, we use pause to wait in a for loop and read the elapsed time approximately every second. Here is a complete example:
function timer_example
t = timer('ExecutionMode', 'fixedRate', ...
'Period', 5, ...
'TimerFcn', #timerCallback); % create timer
start(t); % start timer
pause on; % make sure pause can be used
for i = 1:10
pause(1); % wait a second
disp(getElapsedTime(t)); % display the elapsed time
end
stop(t); % stop timer
delete(t); % delete timer
function timerCallback(timerObj,event) %#ok<INUSD>
disp('Hello World!');
set(timerObj,'UserData',tic);
function retval = getElapsedTime(timerObj)
retval = toc(get(timerObj,'UserData'));
This gives the following output:
>> timer_example
Hello World!
1.0163
2.0173
3.0235
4.0285
Hello World!
0.0366
1.0390
2.0427
3.0461
4.0470
Hello World!
0.0515

Answer 3

Use tic as StartFcn of your timer and then use toc to elicit elapsed time, so:
timerObj = timer; %create timer object
timerObj.ExecutionMode = 'fixedSpacing';
timerObj.Period = 15;
timerObj.StartFcn = #(~,~)tic; % start ticking when timer starts
timerObj.TimerFcn = #myTimerFunc;
myTimerFunc is:
function [] = myTimerFunc(timerObj,event)
% use toc
disp(toc);
end