last question, for my library, the hal also requires an alloc and free function,  any tips on how to handle it and how to give a static evaluated pool size ?
The signature as always is inflexible so no context can be passed...
This is my current super naive impl but the size is fixed:

```rs
static mut MEM: [u8; 42 * 1024] = [0; 42 * 1024];
unsafe extern "C" fn mem_alloc(size: usize) -> *mut c_void {
    let ptr = MEM.as_mut_ptr();
    let mut ptr = ptr.add(size);
    ptr = ptr.offset(-(size as isize));
    ptr as *mut c_void
}

unsafe extern "C" fn mem_free(ptr: *mut c_void) {
    let ptr = ptr as *mut u8;
    let size = MEM.as_mut_ptr().offset_from(ptr) as usize;
    core::ptr::write_bytes(ptr, 0, size);
}
```
any idea ?