To learn more about C and .comp, I tried to add comments (the "// ...
bits") to edge.comp. I am still a bit fuzzy on how edge works so I would
appreciate any improvements to my comments below. Thanks.
------- edge.comp -------
component edge "Edge detector and single pulse generator.";
pin in bit in "Signal with edges to detect";
pin out bit out "Goes high when the desired edge is seen on
'in'";
pin out bit out_invert "Goes low when the desired edge is seen on
'in'";
param rw bit in_edge=TRUE "Selects the desired edge: TRUE means falling,
FALSE means rising";
param rw signed out_width_ns=0 "Time in nanoseconds of the output pulse";
param r signed time_left_ns "Time left in this output pulse";
param r bit last_in "Previous input value";
function _ nofp "Produce output pulses from input edges";
license "GPL";
;;
FUNCTION(_){
int new_in = in; // make a copy of the current in value
if(in_edge) new_in = ! new_in; // If checking for a falling edge,
invert new-in to adjust it to a rising edge, otherwise go to next line
if(new_in && new_in != last_in) { // If new_in is non-zero and
different than last_in, edge is detected?
time_left_ns = out_width_ns; // then reset time_left_ns to the
selected pulse width value
out = 1; out_invert = 0; // and set the outputs to reflect the
edge detection
} else if(time_left_ns > 0) { // otherwise, if there is still some
time left
time_left_ns -= period; // then decrement time_left_ns by the
value of period (the period length of the home thread?)
out = 1; out_invert = 0; // set the outputs to reflect that
the pulse is continuing
} else { // otherwise, the pulse is done
time_left_ns = 0; // reset time left
out = 0; out_invert = 1; // reset outputs to get ready for
next edge detection
}
last_in = new_in; // Save a copy of the current edge
adjusted input to use for the next pass
}
------- edge.comp -------
I would have tended to have made the read only param's as variables, but
I found that variables won't show up in halscope, so I am assuming that
param's were used for this reason? I also would have declared new_in up
in the param section as a variable or param, but I guess "int new_in =
in" kills the declaration and the value assignment with one stone? The
statement "if(new_in && new_in != last_in)" kind of baffles me. "foo &&
foo" seems to be a programming trick called a short circuit? I also
haven't figured out the true meaning of life.
--
Kirk Wallace
http://www.wallacecompany.com/machine_shop/
http://www.wallacecompany.com/E45/index.html
California, USA
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