RIOT/tests/bench/periph_gpio_ll

Benchmark for periph/gpio_ll

This application will generate a square wave on two output pins with a phase difference of zero between them using both the periph/gpio API (as reference) and the periph/gpio_ll API. You can use a logic analyzer or scope to verify that the square waves are indeed simultaneous (no phase difference) and their frequency. Note that with the pin based periph/gpio API a phase difference is expected, but not for the port based periph/gpio_ll API.

In addition, a timer is used to measure the average frequency over 50,000 square wave periods. The overhead of the loop is estimated and a compensated frequency (that would be achievable only by unrolling the loop) is calculated. Both frequencies are printed, in addition to the number of CPU cycles per wave period. The optimal value is 2 CPU cycles (signal is 1 cycle high and 1 cycle low).

Configuration

Configure in the Makefile or set via environment variables the number of the GPIO port to use via the PORT_OUT variable. The PIN_OUT_0 and PIN_OUT_1 variables select the pins to use within that GPIO port. If possible, choose a GPIO port that is fully broken out to pins of your board but left unconnected. That way you can connect a scope or a logic analyzer to verify the output.

Note that the test using gpio_ll_write() might cause changes to unrelated pins on the PORT_OUT GPIO port, by restoring their value to what it was at the beginning of the benchmark.

FAQ

Why are 4 functions calls used for periph/gpio, but only 2 for periph/gpio_ll? This isn't fair!

Since in a port based APIs multiple pins can be accessed at once, only two accesses are needed (one for the high and one for the low part of each square wave period). In the pin based periph/gpio API, two accesses are needed per pin. This unfair advantage in speed is one of the reasons we want a low level port based API in RIOT - in addition to a more convenient to use and high level pin based API.