In some ways this example is a bit illogical. The TLS2561 consumes a few hundred micro amps while operating so using it to wake the STM32L031 from sleep doesn’t make a lot of sense. This example may be relevant to those who want to use an external I/O pin to wake the an STM32L031 generally or maybe as part of a larger circuit.
The TLS2561 can generate an interrupt signal when the received on Channel 0 goes outside a user specified certain range. In this example, the range was arbitrarily set to 0x0000 to 0x100. If the received light is equal to or greater than 0x100 then the interrupt signal is driven low which wakes the MCU. If the light is less than or equal to 0 an interrupt is also generated. This isn’t exactly what I wanted (I only wanted an interrupt if the light was bright) so if the circuit is plunged into complete darkness an interrupt will also be generated. This unintended waking could be dealt with by checking the value on Channel 0 and, if zero, going back to sleep again.
Code is available as usual over on github.