$ halrun
halcmd: loadrt pwmgen output_type=0
halcmd: loadrt threads name1=fast period1=20000 fp1=0 name2=slow period2=1000000 fp1=1
halcmd: addf pwmgen.make-pulses fast
halcmd: addf pwmgen.update slow 
halcmd: setp pwmgen.0.pwm-freq 100
halcmd: setp pwmgen.0.enable 1
halcmd: start
halcmd: loadusr halscope 20000
 
in halscope, select fast thread; set channel 1 to pwmgen.0.pwm; set trigger
source to channel 1 rising; select run mode "normal"