Hands-On RTOS with Microcontrollers

Comparing direct task notifications  to queues

Compared to queues, task notifications have the following features:

• They always have storage capacity of exactly one 32-bit integer.
• They do not offer a means of waiting to push a notification to a busy task; it will either overwrite an existing notification or return immediately without writing.
• They can only be used with only one receiver (since the notification value is stored inside the receiving task).
• They are faster.

Let's take a look at a real-world example using SystemView to compare the direct notification code we just wrote against the first queue implementation.

The queue implementation from mainQueueSimplePassByValue.c looks like this when performing xQueueSend:

The direct task ...