component estop_latch "Software ESTOP latch";

description """
This component can be used as a part of a simple software ESTOP chain.

It has two states: "OK" and "Faulted".

The initial state is "Faulted".  When faulted, the
.B out-ok
output is false,
the
.B fault-out
output is true, and the
.B watchdog
output is unchanging.

The state changes from "Faulted" to "OK" when
.B all
these conditions are true:
.RS
.IP \\(bu
.B fault-in
is false
.IP \\(bu
.B ok-in
is true
.IP \\(bu
.B reset
changes from false to true
.RE

When "OK", the
.B out-ok
output is true, the
.B fault-out
output is false, and the
.B watchdog
output is toggling.

The state changes from "OK" to "Faulted" when
.B any
of the following are true:
.RS
.IP \\(bu
.B fault-in
is true
.IP \\(bu
.B ok-in
is false
.RE

To facilitate using only a single fault source,
.B ok-in
and
.B fault-en
are both set to the non-fault-causing value when no signal is connected.
For estop-latch to ever be able to signal a fault, at least one of these
inputs must be connected.

Typically, an external fault or estop input is connected to \\fBfault-in\\fR,
\\fBiocontrol.0.user-request-enable\\fR is connected to \\fBreset\\fR,
and \\fBok-out\\fR is connected to \\fBiocontrol.0.emc-enable-in\\fB.

In more complex systems, it may be more appropriate to use classicladder to
manage the software portion of the estop chain.
""";

pin in bit ok_in = true;
pin in bit fault_in = false;
pin in bit reset;
pin out bit ok_out = false;
pin out bit fault_out = true;
pin out bit watchdog;
function _ nofp;
option data estop_data;
license "GPL";
author "John Kasunich";
;;

typedef struct { int old_reset; } estop_data;

FUNCTION(_) {
    /* check inputs */
    if ( ok_in && !fault_in) {
	/* no fault conditions, check for reset edge */
	if ( reset && !data.old_reset ) {
	    /* got a rising edge, indicate "OK" on outputs */
	    ok_out = 1;
	    fault_out = 0;
	}
	if( ok_out ) {
	    /* toggle watchdog */
	    watchdog = !watchdog;
	}
    } else {
	/* fault condition exists, trip */
	ok_out = 0;
	fault_out = 1;
    }
    /* store state of reset input for next pass (for edge detect) */
    data.old_reset = reset;
}