2 Overview of HAL drivers The HAL drivers were designed to offer a rich set of APIs and to interact easily with the application upper layers. Each driver consists of a set of functions covering the most common peripheral features. The development of each driver is driven by a common API which standardizes the driver structure， the functions and the parameter names. The HAL drivers consist of a set of driver modules， each module being linked to a standalone peripheral. However， in some cases， the module is linked to a peripheral functional mode. As an example， several modules exist for the USART peripheral： UART driver module， USART driver module， SMARTCARD driver module and IRDA driver module. The HAL main features are the following： ? Cross-family portable set of APIs covering the common peripheral features as well as extension APIs in case of specific peripheral features. ? Three API programming models： polling， interrupt and DMA. ? APIs are RTOS compliant： ? Fully reentrant APIs ? Systematic usage of timeouts in polling mode. ? Peripheral multi-instance support allowing concurrent API calls for multiple instances of a given peripheral （USART1， USART2.。。） ? All HAL APIs implement user-callback functions mechanism： ? Peripheral Init/DeInit HAL APIs can call user-callback functions to perform peripheral system level Initialization/De-Initialization （clock， GPIOs， interrupt， DMA） ? Peripherals interrupt events ? Error events. ? Object locking mechanism： safe hardware access to prevent multiple spurious accesses to shared resources. ? Timeout used for all blocking processes： the timeout can be a simple counter or a timebase