variable pulse detection

[digi001]

I am looking to write verilog to detect either a 20us or 40us pulse (with some tolerance) and do 2 different actions accordingly.

What would be a good way to approach this? State machine?

State 0:
Idle

State 1:
Start Count on Rising Edge of Pulse
If Count > 19uS : State 2
If Pulse Falling Edge :State 0
else :State 1

State 2:
If Pulse Faling Edge within 2us then take action 1
else State 3

State 3:
If Count > 39uS : State 4
else If Pulse Falling edge State 0

State 4:
If Pulse Faling Edge within 2us then take action 2
else State 0


Something like this?

 

[HTA]

This would be one approach if you like sequential logic design. Another one is taking a fast microcontroller or DSP with onboard window timer. Key question is what tolerance you want to achieve(1us or less?).

Enjoy your design work!

 

[ads_ee]

I would try something like this

psuedo code for 20 us pulse detection:

if ( (count > 19 us || count < 21 us) && pulse_falling_edge_detect ) state <= do_action_1
else if (count > 21 us) state <= check_4_40us_pulse
else state <= stay_in_this_state

This would wait for a falling edge pulse during the state in a 2 us window and would exit the state when the count exceeds the window without a falling edge pulse. You could use something similar at the 40 us pulse count.