freertos_tickless_lpc

Overview

This document explains the freertos_tickless example. It shows how the CPU enters the sleep mode and then it is woken up either by expired time delay using low power timer module or by external interrupt caused by a user defined button.

Prepare the Demo

Connect a serial cable from the debug UART port of the board to the PC. Start Tera Term (http://ttssh2.osdn.jp) and make a connection to the virtual serial port.

  1. Start Tera Term

  2. New connection -> Serial

  3. Set appropriate COMx port (x is port number) in Port context menu. Number is provided by operation system and could be different from computer to computer. Select COM number related to virtual serial port. Confirm selected port by OK button.

  4. Set following connection parameters in menu Setup->Serial port… Baud rate: 115200 Data: 8 Parity: none Stop: 1 Flow control: none

  5. Confirm selected parameters by OK button.

Running the demo

After flashing the example to the board the console will start printing the number of tick count periodically when the CPU is running. To wake up the CPU by external interrupt, press the button, that is specified at the beginning of the example (SWx where x is the number of the user defined button). When the button is pressed, the console prints out the “CPU woken up by external interrupt” message.

Example output:

Tickless Demo example Press SWx to wake up the CPU

Tick count : 0 5000 10000 CPU woken up by external interrupt 15000 20000 25000

Explanation of the example

The example application prints the actual tick count number every time after the specified delay. When the vTaskDelay() is called, the CPU enters the sleep mode for that defined period of time.

While the CPU is in sleep mode and the user defined button is pressed, the CPU is woken up by the external interrupt and continues to sleep after the interrupt is handled. The period of time delay is not changed after the external interrupt occurs.

Supported Boards