Microvisor C++ Clock Demo

This rudimentary digital clock sample demonstrates Microvisor application development using C++.

It makes use of a Microvisor Nucleo Development Board and a four-digit seven-segment LED display driven by the Holtek HT16K33 controller. These I²C devices are widely available from electronics suppliers. Interaction with the I² bus is mediated by the STM32U585 HAL (Hardware Abstraction Layer).

Microvisor Configs

The application also makes use of Microvisor's system calls to retrieve a pre-loaded JSON configuration file which is parsed to apply non-default settings to the clock. This shows how you might use cloud-transferred configurations in your own application.

The settings payload is a JSON object:

{ "mode": false,
  "bst": true,
  "brightness": 4,
  "colon": true,
  "flash": false }

The mode value is true for a 24-hour clock, false for a 12-hour AM/PM view. PM time is indicated by ligting the display’s rightmost decimal point.

The value bst is true if you wish the clock to observe daylight savings time when it applies.

Set brightness to a value between 1 and 15 — this is the display brightness.

The values of colon and flash are closely related. The former is true if you would like the display’s center colon to be illuminated. If it is, setting flash to true will cause the colon symbol to turn on and off every second. The board’s user LED will flash in time.

To upload your settings object, use the Microvisor API:

curl -X POST "https://microvisor.twilio.com/v1/Devices/${MV_DEVICE_SID}/Configs" \
    --data-urlencode "Key=prefs" \
    --data-urlencode "Value={\"mode\": false,\"bst\": true,\"brightness\": 4,\"colon\": true,\"flash\": false}" \
    -u ${TWILIO_ACCOUNT_SID}:${TWILIO_AUTH_TOKEN}

Each Config is a key:value pair which your application code can access. The key is prefs. Once uploaed, this Config can be retrieved by the application, which uses the ArdunioJson library to validate and parse the Config’s JSON content.

Working with C++ and the STM32U585 HAL

The STM32U585 HAL is written in C, and to safely receive calls from the HAL, your C++ functions should be declared as external C functions. For example, the sample uses the HAL-defined TIM8 IRQ handler callback TIM8_BRK_IRQHandler(). To ensure this is correctly address by the C++ linker, add a declaration to your .cpp file as follows:

#ifdef __cplusplus
extern "C" void TIM8_BRK_IRQHandler(void);
#endif

Hardware

Adafruit offers an inexpensive HT16K33-based display breakout which you can connect to your Nucleo as follows. CN12 is the right-had GPIO header (with the POWER connector at the top) and CN 11 is on the left (see Nucleo Getting Started Guide for details).

Breakout Pin	Nucleo Pin
SCL	CN12 17
SDA	CN12 5
GND	CN12 71
VCC	CN11 5

Note GND can be connected to any GND pin.

License

This application is © 2024 KORE Wireless and is licensed under the MIT License.

It contains ArduinoJson, which is © 2024 Benoit Blanchon and licensed under the MIT License.