Darian Leung de682a13b1 examples: Update system examples README

The following commit updates the first half of the the system
example README files. Some other changes were also made:

* Updated base_mac_address example
* Moved contents in GCOV README to GCOV docs
* Some *main.c file names updated
* Updated example README template

2019-08-28 16:19:40 +08:00

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FreeRTOS Real Time Stats Example

(See the README.md file in the upper level 'examples' directory for more information about examples.)

FreeRTOS provides the function vTaskGetRunTimeStats() to obtain CPU usage statistics of tasks. However, these statistics are with respect to the entire runtime of FreeRTOS (i.e. run time stats). Furthermore, statistics of vTaskGetRunTimeStats() are only valid whilst the timer for run time statistics has not overflowed.

This example demonstrates how to get CPU usage statistics of tasks with respect to a specified duration (i.e. real time stats) rather than over the entire runtime of FreeRTOS. The print_real_time_stats() function of this example demonstrates how this can be achieved.

How to use example

Hardware Required

This example should be able to run on any commonly available ESP32 development board.

Configure the project

idf.py menuconfig

Select Enable FreeRTOS to collect run time stats under Component Config > FreeRTOS (this should be enabled in the example by default)
Choose the clock source for run time stats configured under Component Config > FreeRTOS. The esp_timer should be selected be default. This option will affect the time unit resolution in which the statistics are measured with respect to.

Build and Flash

Build the project and flash it to the board, then run monitor tool to view serial output:

idf.py -p PORT flash monitor

(Replace PORT with the name of the serial port to use.)

(To exit the serial monitor, type Ctrl-].)

See the Getting Started Guide for full steps to configure and use ESP-IDF to build projects.

Example Output

The example should have the following log output:

...
Getting real time stats over 100 ticks
| Task | Run Time | Percentage
| stats | 1304 | 0%
| IDLE0 | 206251 | 10%
| IDLE1 | 464785 | 23%
| spin2 | 225389 | 11%
| spin0 | 227174 | 11%
| spin4 | 225303 | 11%
| spin1 | 207264 | 10%
| spin3 | 225331 | 11%
| spin5 | 225369 | 11%
| Tmr Svc | 0 | 0%
| esp_timer | 0 | 0%
| ipc1 | 0 | 0%
| ipc0 | 0 | 0%
Real time stats obtained
...

Example Breakdown

Spin tasks

During the examples initialization process, multiple spin tasks are created. These tasks will simply spin a certain number of CPU cycles to consume CPU time, then block for a predetermined period.

Understanding the stats

From the log output, it can be seen that the spin tasks consume nearly an equal amount of time over the specified stats collection period of print_real_time_stats(). The real time stats also display the CPU time consumption of other tasks created by default in ESP-IDF (e.g. IDLE and ipc tasks).

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