Hands-On RTOS with Microcontrollers

Pros and cons of a polled driver

Here are some of the advantages of using a polled driver:

• It is easy to program.
• Any task has immediate access to data in the queue.

At the same time, there are many issues with this approach:

• It must be one of the highest priority tasks in the system.
• There is a high chance of data loss when not executing at high priority.
• It is extremely wasteful of CPU cycles.

In this example, we're only transferring data at 9,600 baud. Granted, most of the time was spent spinning on the RXNE bit, but transferring every byte as it is received in a queue is also fairly expensive (when compared to pushing bytes into a simple array-based buffer). To put this into perspective, USART2 on STM32F767 running at 216 MHz has ...