Delay above ms not working

iain93

Hi,

I'm trying to program a fastino with a delay. However, I've notice anything above 5ms the system just skips over. Is this correct? The final use case is setting the output to a DC voltage and then after some time (seconds) to turn it off or to a lower voltage. Can this not be done? What is the correct way to do this?

from artiq.experiment import *

class fastio(EnvExperiment):
    """fastio with changing time"""
    def build(self):
        self.setattr_device("core")
        self.setattr_device("fastino0")
        
    def prepare(self):
        self.voltages = [5.0,1.0]

    @kernel
    def run(self):
        self.core.reset()
        self.core.break_realtime()
        self.fastino0.init()
        delay(1*ms)
        self.fastino0.set_leds(0x55)
        delay(1*ms)
        print("Start", self.core.get_rtio_counter_mu())
        for i in range(len(self.voltages)):
            self.fastino0.set_dac(0, self.voltages[i])
            delay(10.0)
            print("Mid",i, self.core.get_rtio_counter_mu())
        self.fastino0.set_leds(0xAA)
        delay(1*ms)
        print("End", self.core.get_rtio_counter_mu())

Output:

INFO:worker(120,fast2.py):print:Start 141306383312
INFO:worker(120,fast2.py):print:Mid 0 141306593616
INFO:worker(120,fast2.py):print:Mid 1 141306713752
INFO:worker(120,fast2.py):print:End 14130690989600000000000000

sb10q

iain93 I've notice anything above 5ms the system just skips over. Is this correct?

No.

Guest

Ok, can you advise what in my logic i am doing wrong? Or which part of the documentation i need to be understanding?

asc

The trick you have to see here is that delay() is moving the rtio pointer, while get get_rtio_counter_mu() is looking at the position of the actual RTIO clock time. When you call delay(), it's not like doing time.sleep() - the function returns immediately and all that happens is you change when in time to schedule the next event. If you look at an oscilloscope, the result is probably what you expect. The relevant bit of documentation is the description of the RTIO system, and how the time pointer works.

Also, be very careful about using print() statements inside quick timing loops. print() uses an RPC, so it takes a fair bit of time to ship the data out to the host computer and wait for a response (potentially a few ms), so this can quickly consume a lot of slack and cause underflow problems.