CityHub and Technic Motor 46 - Port controller slow to start

[toyotafj40]

I developed some code last year with a CityHub driving a Technic Motor type 46. There were never any issues at startup and the motor was reliable.

Recently I embarked on a new project with the CityHub and now have PORT INIT issues at start-up, but only when NOT connecting to the GATT service.

The new application is a SLAVE hub and is quick to boot up - it just loads from Flash, initialises BLE and then the Ports.

It seems that if I wait 3 blue flashes after hub power-up, then press the hub button again to start the program, then the PORT initialises correctly.

If I press the power-up and start close together, the PORT init can't see motor type 46.

To overcome that, I just keep polling for 5 seconds until the port initialises correctly.

I have attached an extract from the program to demonstrate the issue. (Hub running Pybricks Code v3.0.1 with firmware v4.0.1)

import gc

from pybricks.iodevices     import PUPDevice
from pybricks.parameters    import Direction, Port, Color
from pybricks.pupdevices    import Motor, DCMotor, Light

from pybricks.hubs          import CityHub

from micropython            import const
from pybricks.tools         import wait

gc.collect()
HUB = CityHub()
gc.collect()

#################   CONSTANTS            ##########################################

# ============================================================
# DEVICES
# ============================================================

MOTOR_WEDO              = const (1)
MOTOR_TRAIN             = const (2)
LED_LIGHT               = const (8)
MOTOR_LARGE             = const (46)
MOTOR                   = const (65)


# ============================================================
# COLOURS
# ============================================================

NONE                    = const(0)
RED                     = const(8)
WHITE                   = const(10)

COLORS = (
    Color.NONE,             # 0
    Color.RED,
    Color.WHITE,            # 10
)

#################   GLOBALS              ##########################################

class System_State:

    Configure_Ports = True

    Port_A_Device   = None
    Output_Port_A   = 0
    Motor_PWM       = 0


sys = System_State()


#################   PORT ALLOCATIONS     ##########################################

def _Show_Detect (port, device):

    if device == 1:     text = "Wedo Motor"
    elif device == 2:   text = "Train Motor"
    elif device == 8:   text = "LED Light"
    elif device == 46:  text = "Technic Motor"
    elif device == 65:  text = "Motor - Large"
    else: text = "Unknown"

    print (port," : ", device, " : ", text)


def Configure_PORTS():

    if sys.Port_A_Device is None:

        sys.Port_A_Device = Port_Detect(Port.A)
        _Show_Detect ("Port.A", sys.Port_A_Device)

        sys.Output_Port_A = _Port_Allocate (Port.A, sys.Port_A_Device)

        HUB.light.on(Color.WHITE)
        wait(250)


def _Port_Allocate(port, device):

    output = 0
    gc.collect()

    try:
        if (device) == MOTOR_LARGE:  
            output = Motor(port, Direction.CLOCKWISE)

        if (device) == MOTOR_TRAIN:
            output = DCMotor(port, Direction.CLOCKWISE)

        if (device) == LED_LIGHT:
            output = Light(port)

    except OSError:
        gc.collect()                                                            # No device found on this port.

    return output

def Port_Detect (port):                                                         # Find out what is plugged in

    try:                                                                        
        device = PUPDevice(port)
        value = device.info()['id']

    except OSError:
        HUB.light.on(Color.RED)
        wait(25)
        return None                                                              

    if value == 0 or value == LED_LIGHT:
        return value

    elif value <= MOTOR_TRAIN or value >= MOTOR:                               # Simple DC Motor Types = 1, 2, 65, 75 , 76
        return MOTOR_TRAIN

    return MOTOR_LARGE  

def _Port_OUTPUT (port, device, mode, value, lo = False):       
  
    if mode == MOTOR:
        if device == MOTOR_LARGE or device == MOTOR_TRAIN :

            #print (port, device, mode, value, lo )

            if value == 0 :
                port.stop()
            else:
                port.dc(value)                                  # Duty Cycle output = Speed

            if lo == True:
                port.close()
          
    if mode == LED_LIGHT:
        if device == LED_LIGHT:
            if value != 0:
                port.on(abs(value))
                return

            port.off()

#######################
# START
#######################


Speed = 5
UpDown = 1

while True:
    Configure_PORTS()

    if UpDown : Speed += 5
    if not UpDown : Speed -= 5

    if Speed >= 50: UpDown = 0
    if Speed <= 5: HUB.system.shutdown()     # Shutdown after one loop

    _Port_OUTPUT(                                          # Send received Motor_PWM to Output Port.A                                   
        sys.Output_Port_A,
        sys.Port_A_Device,
        MOTOR,
        Speed,
        False )

    wait (250)

When the HUB is plugged into the Type 46 Technic Motor, and the hub started, the HUB LED flashes RED (50ms) for each retry.

The part I can't quite resolve is the old code is very similar and does work, but I can't work out the difference...

def Port_Allocate (device, port, text, temp, mode, _Bright_A):                  # _Left_ROW, Port.A, _EE_PORT_ROT_A, _EE_SLAVE_ROT_A, _HUB_Mode, _Bright_A
    
    output = 0
    gc.collect()

    if mode == "MASTER":
        spin_direction = Load_Rotation (text)
    else:
        spin_direction = Load_Rotation (temp)
 
    try:
        if (device) == MOTOR_LARGE:  
            output = Motor(port, Rotate_DIR (spin_direction))

        if (device) == MOTOR_TRAIN:
            output = DCMotor(port, Rotate_DIR (spin_direction))

        if (device) == LED_LIGHT:
            output = Light(port)
            Port_OUTPUT (output, device, _LED_LIGHT, _Bright_A, 0)

    except OSError:
        gc.collect()                                                            # No device found on this port.

    return output

def Port_Detect (port):                                                         # Find out what is plugged in

    try:                                                                        
        device = PUPDevice(port)
        value = device.info()['id']
    except OSError:
        return 0                                                                # _Port_A_Device = Port_Detect(port.A)

    if value == 0 or value == LED_LIGHT:
        return value

    elif value <= MOTOR_TRAIN or value >= MOTOR:                           # Simple DC Motor Types = 1, 2, 65, 75 , 76
        return MOTOR_TRAIN

    return MOTOR_LARGE  

[dlech]

We just released a v4.1.0b3 firmware at https://beta.pybricks.com. Does the problem still happen with that firmware version?

[toyotafj40]

Same result with the latest firmware.

Anyway, the workaround is to poll the device for a short time. It usually responds correctly after 2 - 3 seconds.
Fortunately, it is consistent with the standard train motor, which is what most of my trains will run.

[BertLindeman]

Could not confirm the problem with your first program.

Connected to:	city v4.0.1
Hub type:	City Hub
Firmware:	v4.0.1

No red blink seen in 5 tests.

Also tried the same program on a v4.1.0b2 CityHub and that works fine too.

[laurensvalk]

Sometimes the motors do take a few seconds to start up.

We are supposed to gracefully wait in that case, but it sounds like an error is being raised.