Deprecation note!

Please note: this repository is deprecated and is no longer actively maintained.

Mbed 3 utilities library

Implementation of various generic data structures and algorithms used in mbed.

Configuration

Some parameters of the core-util library can be configured in yotta. Currently, core-util supports configuring two things: the argument storage size of FunctionPointerBind and whether or not FunctionPointer checks its arguments before calling

Configuring the storage size for FunctionPointerBind's bound arguments

In some cases it may be necessary to increase FunctionPointerBind's argument size. In others, for memory optimization, it may be necessary to decrease the size of FunctionPointerBind's bound arguments. If either of these are necessary, adding a new key with yotta config will allow this configuration: "util": {"functionPointer":{"arg-storage" : <bytes>}}.

Configuring whether or not FunctionPointer checks its arguments before calling

For debug purposes, it is possible to have FunctionPointer check its arguments before being called. If it checks its arguments, it will use a CORE_UTIL_ASSERT. Checks can be disabled with: "util": {"functionPointer":{"disable-null-check" : true}}

Atomic operations

This module provides three atomic primitives:

• atomic_cas
• atomic_incr
• atomic_decr

The most versatile API is atomic_cas which provides the facility to implement any other atomic API. The base versions of atomic_incr and atomic_decr are implemented using atomic_cas.

Writing atomic operations

It is possible to implement all atomic operations using atomic_cas and this API is portable across platforms. When writing a new atomic operation, best practice is to implement it using existing atomic operations, which are cross-platform. If an optimization is needed, then it should be a specialization of the portable implementation, which compiles for a specific target.

Example of writing an atomic operation

To illustrate how to write an atomic operation, consider atomic_add. The signature of atomic_add will be:

/**
 * atomic_add
 * Add a non-atomic value to an atomic variable and store the result back to the atomic variable.
 * @param[in,out] ptr The atomic variable
 * @param[in] val The non-atomic value
 *
 * @return the value of the atomic variable after the addition
 */
template <typename T>
T atomic_add(T * ptr, T val);

The first implementation for this API is the generic, portable implementation:

template <typename T>
T atomic_add(T * ptr, T val)
{
    T oldValue = *ptr;
    T newValue;
    do {
        newValue = oldValue + val;
    //This compares oldValue to *ptr, and updates oldValue if *ptr has changed
    } while (!atomic_cas(ptr, &oldValue, newValue));
    return newValue;
}

If a more optimized version is required, the next step is to provide a template specialization which is conditionally selected, based on the processor. The specialization must be declared in the atomic_ops.h header, and the implementation must be defined in the atomic_ops.cpp source file.

Here is an example implementation:

#if (__CORTEX_M >= 0x03)
template<>
uint32_t atomic_add(uint32_t * ptr, uint32_t val)
{
    uint32_t newValue;
    do {
        newValue = __LDREXW(ptr) + val;
    } while (__STREXW(newValue, ptr));
    return newValue;
}
#endif