Practical approach to hardware semaphores

A semaphore is a variable or abstract data type that provides a simple but useful abstraction for controlling access by multiple processes to a common resource in a parallel programming or multi-user environment.

Semaphores are the predominant method in access control in parallel programming and multi-threaded programming environments since their invention in 1965 by the late Edsger Dijkstra, a Dutch computer scientist. Although the semaphore concept was further enhanced from its original principle into many variations, they all serve a similar purpose: to grant access to shared resources without race conditions.

This practical approach to hardware semaphores provides simple semaphore routines that lock, unlock, and reset semaphore gates (flags). These routines are non-blocking and reentrant functions suitable for multi-core application usage. This application note presents each routine with C code, followed by a detailed explanation of its functionality.

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Originally published by Freescale Semiconductor at www.freescale.com as "A Practical Approach to Hardware Semaphores".