Watchdog
The watchdog must be petted by LinuxCNC periodically or it will bite. When the watchdog bites, all the board’s I/O pins are pulled low and the stepgen will stop (optionally the stepgen can stop while respecting the acceleration limits, see description). Encoder instances keep counting quadrature pulses.
Resetting the watchdog resumes normal operation of the FPGA.
Configuration
The configuration of the Watchdog consist of an optional Enable-pin. The Enable-pin is active high as long as the watchdog is happy (communications are working, watchdog did not bite). The enable pin can for example be used to disconnect all pins (high-Z) when the watchdog bites; this can ensure a safe-state of the machine when the communications are lost.
...
"watchdog": {
"pin":"ena:0"
},
...
One can opt not to define a Enable-pin, however this is not recommended as there is a risk of the machine staying active after disruption of the communications. Even when the enable pin is not defined, the configuration block is required, however it remains empty.
...
"watchdog": {
},
...
Input pins
Name |
Type |
Description |
|---|---|---|
<board-name>.watchdog.timeout_ns |
integer |
The time out (in ns) after which the watchdog will bite. It is recommended to set the watchdog at least 1.5 times the period of the servo-thread to give some leeway. If set too tight, this will lead to a watchdog which bites as soon as there is a latency excursion. |
Output pins
Name |
Type |
Description |
|---|---|---|
<board-name>.watchdog.has_bitten |
hal_bit (i/o) |
Flag indicating that the watchdog has not been petted on time and that it has bitten. should be set to False or 0 to restart the working of the FPGA |
<board-name>.watchdog.timeout_cycles |
integer |
The number of cycles of the FPGA before the watchdog bites (DEBUG). |
Example
loadrt threads name1=servo-thread period1=10000000
loadrt litexcnc connections="<connnection_string>"
loadrt estop_latch
# Add the functions to the HAL
addf <board-name>.read test-thread
...
addf estop-latch.0 servo-thread
...
addf <board-name>.write test-thread
# Setup the watchdog (assuming servo-thread period of 1000000 ns (1 kHz))
setp EMCO5.watchdog.timeout_ns 1500000
# Tie the watchdog into the E-STOP chain
net estop-loopout iocontrol.0.emc-enable-in <= estop-latch.0.ok-out
net estop-loopin iocontrol.0.user-enable-out => estop-latch.0.ok-in
net estop-reset iocontrol.0.user-request-enable => estop-latch.0.reset
net remote-estop estop-latch.0.fault-in <= <board-name>.watchdog.has_bitten
# More sources for E-stop (such as a GPIO-in) can be added to this E-Stop circuit.