mbed OS Functions and Usages
26 March 2021
Writer: Gökhan Koçmarlı
CSE2037 | Marmara University
This document is a API referance.Some of the text are copied from the original mbed OS API documentation. I have declare no rights in any of texts.
Digital I/O
| Mode | Description | |
|---|---|---|
| DigitalIn varName(pinNumber) | Digital | For declaring a pin as a digital input source. |
| DigitalOut varName(pinNumber) | Digital | For declaring a pin as a digital output source. |
| varName.read() | Digital | To read the digital value of the varName's pin. (0 || 1) |
| varName.write(value) | Digital | To write value to the varName's pin. |
Analog I/O
| Mode | Description | |
|---|---|---|
| AnalogIn varName(pinNumber) | Analog | For declaring a pin as a analog input source. |
| AnalogOut varName(pinNumber) | Analog | For declaring a pin as an analog output source. |
| varName.read() | Analog | To read the voltage value of the varName's pin [0.0-1.0]. |
| varName.read_u16() | Analog | To read the voltage value as an unsigned short in the range [0x0-0xFFFF]. |
| varName.read_voltage() | Analog | To read the voltage as in units of volts. Doesn't work in Simulator. |
| varName.write(value) | Analog | Set the output voltage with specifing as a percentage value (float). |
| varName.write_u16(value) | Anlog | Set the output voltage represented as a unsigned short in range [0x0, 0xFFFF] |
Interrupts
| Mode | Description | |
|---|---|---|
| InterruptIn varName(pinNumber) | Interrupt | For declaring a pin as an GPIO interrupt source. |
- No blocking code in ISR: avoid any call to wait, infinite while loop or blocking calls in general.
- No printf, malloc or new in ISR: avoid any call to bulky library functions. In particular, certain library functions (such as printf, malloc and new) are non re-entrant, and their behavior could be corrupted when called from an ISR.
- For
printfsfrom interrupt context, use Event instead.
Timers
| Mode | Description | |
|---|---|---|
| Timer varName | Timer | To initalize a timer which is stopwatch-like timer for measuring precise times. |
| varName.start() | Timer | Start counting the time. |
| varName.stop() | Timer | Stop counting the time. |
| varName.read() | Timer (float) | Read the value of time as sec. Deprectated since 6.0 |
| varName.read_ms() | Timer (int) | Read the value of time as miliseconds. Deprectated since 6.0 |
| varName.read_us() | Timer (int) | Read the value of time as microseconds. Deprectated since 6.0 |
| varName.read_high_resolution_us() | Timer (us_timestamp_t) | 64bit microseconds value. Deprectated since 6.0 |
| Ticker varName | Ticker | To set up a recurring interrupt; it calls a function repeatedly and at a specified rate. |
| varName.attach() | Ticker | Attach a function to be called by the Ticker, specifying the interval in seconds. |
| varName.attach_us() | Ticker | Attach a function to be called by the Ticker, specifying the interval in microseconds. |
| varName.detach() | Ticker | To detach the ISR. |
| Timeout varName | Timeout | To set up an interrupt to call a function after a specified delay. |
| varName.attach() | Timeout | Attach a function to be called by the Ticker, specifying the interval in seconds. |
| varName.attach_us() | Timeout | Attach a function to be called by the Ticker, specifying the interval in microseconds. |
| varName.detach() | Timeout | To detach the ISR. |
You can also use LowPowerTimer, LowPowerTicker, and LowPowerTimout for better power management. You must consider that LowPower*s has worse precision than the normal ones but the normals can not enter the deep sleep mode. Their methods are the same.
- Timers are based on 64-bit signed microsecond counters, giving a range of over 250,000 years.
- No printf, malloc or new in ISR: avoid any call to bulky library functions. In particular, certain library functions (such as printf, malloc and new) are not re-entrant, and their behavior could be corrupted when called from an ISR.
- While a Timer is running, deep sleep is blocked to maintain accurate timing. If you don't need microsecond precision, consider using the LowPowerTimer or Kernel::Clock classes instead because these do not block deep sleep mode.
- While an event is attached to a Ticker, deep sleep is blocked to maintain accurate timing. If you don't need microsecond precision, consider using the LowPowerTicker class instead because that does not block deep sleep mode.
| Mode | Description | |
|---|---|---|
| Watchdog &varName = Watchdog::get_instance() | Watchdog | Initalizing the watchdog timer. |
| varName.start(TIMEOUT_IN_MS) | Watchdog | Starting the watchdog timer. |
| varName.stop() | Watchdog | Stopping the watchdog timer. |
| Watchdog::get_instance().kick() | Watchdog | Refreshing the timer. |
| varName.is_running() | Watchdog | Checking if it's already running. |
- There is only one instance in the system. Use Watchdog::get_instance() to obtain a reference.
- The maximum amount of time you can set as the Watchdog timeout varies depending on the target hardware. You can check the maximum value by calling Watchdog::get_instance().get_max_timeout().
Pulse Witdh Modulation
| Mode | Description | |
|---|---|---|
| PwmOut varName(pinNumber) | PWM | For declaring a pin as a PWM output source. |
| varName.write(value) | PWM | Setting the duty cycle in range (0.0-1.0) |
| varName.write(value) | PWM | Read the current duty cycle. |
| varName.period(value) varName.period_ms(value) varName.period_us(value) |
PWM | Setting the PWM's period as seconds (float), milli-seconds (int) and micro-seconds (int). |
| varName.pulsewidth(value) varName.pulsewidth_ms(value) varName.pulsewidth_us(value) |
PWM | Setting the PWM's pulsewidth as seconds (float), milli-seconds (int) and micro-seconds (int) and keeping the period the same. |
| varName.suspend() | PWM | Suspending the PWM signal |
| varName.resume() | PWM | Resuming the PWM signal |
- Set the cycle time first, and then set the duty cycle using either a relative time period via the write() function or an absolute time period using the pulsewidth() function.
- The default period is 0.020s, and the default pulse width is 0.