This library communicates with PWM servos.
Pulse Width Modulation (PWM) is a protocol for receivers to send commands to servos. Each servo is sent a high pulse with the width of the pulse dictating the commanded position. Traditionally, PWM commands are sent at a 50 Hz interval with pulse widths varying between 1000 us and 2000 us. Some servos and Electronic Speed Controllers (ESCs) support higher frequencies, which typically requires a shorter pulse width range. PWM is the most common protocol for sending servo and ESC commands, but they require a PWM capable pin for each servo being controlled.
CMake is used to build this library, which is exported as a library target called pwm. The header is added as:
#include "pwm/pwm.h"
The library can be also be compiled stand-alone using the CMake idiom of creating a build directory and then, from within that directory issuing:
cmake .. -DMCU=MK66FX1M0
make
This will build the library and example executable called pwm_example. The example executable source file is located at examples/pwm_example.cc. Notice that the cmake command includes a define specifying the microcontroller the code is being compiled for. This is required to correctly configure the code, CPU frequency, and compile/linker options. The available MCUs are:
- MK20DX128
- MK20DX256
- MK64FX512
- MK66FX1M0
- MKL26Z64
- IMXRT1062_T40
- IMXRT1062_T41
These are known to work with the same packages used in Teensy products. Also switching the packages is known to work well, as long as it's only a package change.
The pwm_example target creates an executable for communicating with PWM servos. This target also has a _hex for creating the hex file to upload to the microcontroller.
This library is within the namespace bfs
PwmTx This class is templated with the number of PWM pins.
std::array<int8_t, 6> pins = {21, 22, 23, 2, 3, 4};
bfs::PwmTx<pins.size()> pwm;void Init(const std::array<int8_t, N> &pins) Initializes the PWM pins given an array of pin numbers.
pwm.Init(pins);void Write() Sends the PWM commands to the servos.
pwm.Write();static constexpr int8_t NUM_CH Returns the number of PWM channels.
void ch(const std::array<int16_t, N> &ref) Updates the PWM commands.
std::array<int16_t, pwm.NUM_CH> cmd = {1000, 1200, 1300, 1400, 1500, 1600};
pwm.ch(cmd);std::array<int16_t, N> ch() Returns an array of the PWM commands.