Random Number Generator API

[alexandruCarp]

Fixes #25.
Implemented the API and an example app which asks for some random numbers and prints them.
The app works fine on the microbit.
Added fake driver and tests.

[alexandruradovici]

Please rebase this.

[alexandruradovici]

@alexandruCarp any updates here?

[alexandruCarp]

I don't think it is possible to also check the buffer size for the async generation, so I guess I will leave that with the behavior of the driver (which is to only write buf.len() bytes if more are requested). The sync function now returns SIZE error in this case. Is there anything else I should do?

[alexandruradovici]

What do that two u32 values from the listener mean?

[alexandruCarp]

The first one is always 0, and the second one represents the number of random bytes successfuly written in the buffer.

[alexandruradovici]

Similar to

https://github.com/DanutAldea/libtock-rs/blob/b70eb0cbe1766a37585472235e77f755a7c12786/apis/ambient_light/src/lib.rs#L67-L73

I suggest adding a RandomDataListener, as the user wants to get a function called when data is available.

pub struct RandomDataListener<share etc, F: Fn(&'share [u8])>(pub F);

impl<F: Fn(u32)> Upcall<OneId<DRIVER_NUM, 0>> for IntensityListener<F> {
    fn upcall(&self, _arg0: u32, len: u32, _arg2: u32) {
        // unshare buffer
        f(buffer[0..len]);
        // share buffer back
    }
}

Add an unregister_listener function that returns Result<&'share [u8], ErrorCode> to unshare the buffer earlier.

[alexandruradovici]

I suggest writing a RandomListener similar to:

struct RandomListener<'a> {
    buffer: &'a mut [u8]
}

impl RandomListener {
   pub fn new (buffer: &'a mut [u8]) {...}
}

The generate_random function will get this listener as an argument an share it with the driver.

[alexandruradovici]

Similar to

https://github.com/DanutAldea/libtock-rs/blob/b70eb0cbe1766a37585472235e77f755a7c12786/apis/ambient_light/src/lib.rs#L67-L73

I suggest adding a RandomDataListener, as the user wants to get a function called when data is available.

pub struct RandomDataListener<share etc, F: Fn(&'share [u8])>(pub F);

impl<F: Fn(u32)> Upcall<OneId<DRIVER_NUM, 0>> for IntensityListener<F> {
    fn upcall(&self, _arg0: u32, len: u32, _arg2: u32) {
        // unshare buffer
        f(buffer[0..len]);
        // share buffer back
    }
}

Add an unregister_listener function that returns Result<&'share [u8], ErrorCode> to unshare the buffer earlier.

[alexandruradovici]

Suggested change

	pub fn register_listener<'share>(
	pub fn register_listener<'share>(&'share mut buffer,
	listener: &'share RandomDataListener,

[alexandruCarp]

I tried to implement these changes but I don't know how could that unregister_listener function return the buffer (where would it get it from). I also don't understand how could I share the buffer back from the listener.