C-DAQ Hot Module Swap

[jazzleblue]

I have a service which polls every few seconds or so that the chassis is alive, modules present, etc in our c-daq chassis. I have noticed when hot plugging/unplugging a device on a c-daq chassis it will cause the System instance to hang or become unresponsive. I could catch that and restart it but wondered if I needed to handle hot actions in the chassis differently or not at all supported? Didn't want to post as an issue if it is working as intended.

[zhindes]

System instance to hang or become unresponsive

Can you be more specific? Does a method/property call not return? If you shared your code and annotated a bit what happens when it "hangs" that would be useful.

FWIW, for this type of operation it is probably best to use the nisyscfg module (github). That is what is used for things like NI MAX and Hardware Configuration Utility to operate. Something like this will list all modules plugged into a cDAQ chassis (untested):

import nisyscfg
with nisyscfg.Session() as session:
    # Print user aliases for all National Instruments devices in the local system
    filter = session.create_filter()
    filter.is_present = True
    filter.is_ni_product = True
    filter.is_device = True
    filter.connects_to_bus_type = nisyscfg.BusType.COMPACT_DAQ
    for resource in session.find_hardware(filter):
        print(resource.expert_user_alias[0])

The underlying implementation of both nisyscfg and what DAQmx uses for the System instance is similar, though. So what you're doing is probably also fine.

[jazzleblue]

Every five seconds this runs to look for NI stuff:

def _get_chassis(self) -> List[Dict]:
        """Get a list of all NI-DAQ chassis on the network."""
        chassis_list = []
        try:
            device_filter = self.ni_syscfg.create_filter()
            device_filter.is_ni_product = True
            device_filter.is_chassis = True
            devices = self.ni_syscfg.find_hardware(device_filter)
            for device in devices:
                chassis_info = {
                    "name": device.name,
                    "serial_number": device.serial_number,
                    "ip_address": device.tcp_ip_address,
                    "host_name": device.tcp_host_name,
                    "firmware_version": device.firmware_revision,
                    "model": device.product_name,
                }
                chassis_list.append(chassis_info)
        except Exception as e:
            logger.error(f"Error in _get_chassis: {str(e)}")
        return chassis_list

def _get_modules(self, chassis: str) -> List[Dict]:
    """Get a list of all modules for a given chassis."""
    module_list = []
    try:
        device_filter = self.ni_syscfg.create_filter()
        device_filter.is_ni_product = True
        device_filter.is_chassis = False
        device_filter.number_of_slots = False
        device_filter.name = f"*{chassis}*"
        devices = self.ni_syscfg.find_hardware(device_filter)
        for device in devices:
            module_info = {
                "name": device.name,
                "serial_number": device.serial_number,
                "model": device.product_name,
                "slot_number": device.slot_number,
                "chassis": chassis,
            }
            logger.debug(f"Module found: {device.name}")
            if device.name.startswith(chassis):
                module_info["sub_module"] = False
            else:
                module_info["sub_module"] = True
            module_list.append(module_info)
    except Exception as e:
        logger.error(f"Error in _get_modules for chassis {chassis}: {str(e)}")
    return module_list

If I hot plug/unplug a module in the c-daq the find_hardware call will hang. I will be debugging a bit more tomorrow to absolutely make sure that is where the hang is...but if I don't touch the physical modules all is well in the world.

[jazzleblue]

And you may ask a very valid question. Why isn't this posted in nisyscfg? Well this issue has persisted for quite a long time and I just came back to it and forgot I moved all of the polling to the nisyscfg library. The local instance/db is created by calling nidaqmx but nisyscfg is used after that for many things. So probably should move it there and ask Tyler for discussion if it is truly hanging where I think it is. Anywho..thanks for reading!

[zhindes]

FWIW, I don't think Tyler/nisyscfg would have much useful to add. If there is a hang, its probably within the nisyscfg DLL or in a nisyscfg sub-expert misbehaving (probably the DAQ one?). This isn't really the right place for that either since these Python bindings are at a level above all that, but you have my curiosity piqued.

[zhindes]

This code worked for me. The main difference is that I don't have an ethernet chassis, which you seem to have. Anything else I got wrong? Definitely interested in where its hanging specifically from your debugging.

import logging
import nisyscfg
import time

logger = logging.getLogger(__name__)

def get_chassis(session: nisyscfg.Session, ) -> list[dict]:
        """Get a list of all NI-DAQ chassis on the network."""
        chassis_list = []
        try:
            device_filter = session.create_filter()
            device_filter.is_ni_product = True
            device_filter.is_chassis = True
            devices = session.find_hardware(device_filter)
            for device in devices:
                chassis_info = {
                    "name": device.name,
                    "serial_number": device.serial_number,
                    # "ip_address": device.tcp_ip_address,
                    # "host_name": device.tcp_host_name,
                    # "firmware_version": device.firmware_revision,
                    "model": device.product_name,
                    "link_name": device.provides_link_name,
                    "is_present": device.is_present
                }
                chassis_list.append(chassis_info)
        except Exception as e:
            logger.error(f"Error in _get_chassis: {str(e)}")
        return chassis_list

def get_modules(session: nisyscfg.Session, chassis_link_name: str) -> list[dict]:
    """Get a list of all modules for a given chassis."""
    module_list = []
    try:
        device_filter = session.create_filter()
        device_filter.is_ni_product = True
        device_filter.is_chassis = False
        device_filter.connects_to_link_name = chassis_link_name
        
        devices = session.find_hardware(device_filter)
        for device in devices:
            module_info = {
                "name": device.name,
                "serial_number": device.serial_number,
                "model": device.product_name,
                "slot_number": device.slot_number,
                "is_present": device.is_present
            }
            module_list.append(module_info)
    except Exception as e:
        logger.error(f"Error in _get_modules for chassis {chassis}: {str(e)}")
    return module_list

if __name__ == "__main__":
    while True:
        with nisyscfg.Session() as session:
            all_chassis = get_chassis(session)
            for chassis in all_chassis:
                print(f"Found {chassis['model']} (S/N: {chassis['serial_number']}): {chassis['name']} (Present: {chassis['is_present']})")
                for module in get_modules(session, chassis['link_name']):
                    print(f"Found {module['model']} (S/N: {module['serial_number']}): {module['name']} (Present: {module['is_present']})")

        for i in range(5):
            print('.', end='', flush=True)
            time.sleep(1.0)
        print()