Turning on the radio by default

[microbit-carlos]

For the micro:bit radio to be used example programmes are usually like this:

import radio

radio.on()
radio.send('hello')

from microbit import *
import radio

radio.on()
while True:
    message = radio.receive()
    if message:
        display.scroll(message)

In all cases radio.on() is necessary to start using the radio, otherwise functions like radio.send() or radio.receive() will throw an exception ValueError: radio is not enabled.

The majority of the micro:bit features, specially those that can be turned off like the display, are "on" by default.
The reason this is not the case for radio is because it has a significant impact on power consumption, about 10 mA as measure by Damien from USB, however:

• The majority of programmes turn on the radio immediately after import, so no difference there
• Any power conscious applications would still have the option to turn on and off the radio as needed

If we are to enable the radio by default we have two options:
a) Do it on import
- Disadvantage: If an existing programme runs a lot of code before calling radio.on(), this is time with a larger power consumption
b) Do it on the first call of radio.send()/.receive()/etc
- Disadvantage: In this case the first call of radio.receive() would only turn on the radio, as it cannot receive anything while it's off

We also need to consider if this would be a breaking change, as ideally we'd like to avoid that.

And, of course, we would have to mirror this to the MicroPython for V1 port.

[microbit-carlos]

About this being a breaking change or not, the majority of programmes would behave more or less the same, some of the biggest differences I can think of are:

Larger power consumption
In programmes like this the additional power consumption might be noticeable:

import radio

# A lot of code executed here before sending data

radio.on()
radio.send("hello")

Expected Exceptions might not be thrown
This would not throw an exception and therefore wouldn't print anything:

import radio

while True:
    try:
        radio.send("hello")
    except ValueError:
        print("turning on radio")
        radio.on()

---

Any other examples for consideration are very welcome.

[microbit-carlos]

a) Do it on import

• Disadvantage: If an existing programme runs a lot of code before calling radio.on(), this is time with a larger power consumption
  b) Do it on the first call of radio.send()/.receive()/etc
• Disadvantage: In this case the first call of radio.receive() would only turn on the radio, as it cannot receive anything while it's off

From these two options I think a) is better. This way it works out of the box, no incoming radio messages are missed, and a user can always do radio.off() immediately after import to conserve energy.

[microbit-carlos]

Decided to turn on the radio on import ✅

[dpgeorge]

Done in ca108e7