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Espruino/targets/esp32/docs/HardwareTimer.md
jumjum123 6c5e37d6d2 Corrected use of Arduino libs, they are not necessary anymore, since we now have spi and i2c in standard drivers 
Added some categories to tasksInterruptsetc
New docu to give some information about hardware timer
Added description of notification between tasks
2017-01-13 13:46:14 +01:00

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Hardware Timer

Espruino uses Highspeed hardware timer for functions like waveform.

##General## ESP32 supports 2 groups of timer, both having 2 timer. esp-idf supports driver for timer with components/driver/include/driver/timer.h

##Conection to Espruino## An interrupt needs to be defined with IRAM_ATTR. To connect to Espruino, the isr (interrupt service routine) calls jstUtilTimerInterruptHandler.

##Problem## This function is not defined as IRAM_ATTR or something similiar. Due to this, or whatever other reason we get a reset after some calls. There could be many reasons for that like:

  • problems with floating point
  • running out of memory, since isr use their own stack
  • running out of time for isr
  • something else ???

##Solution## As long as we don't know better, the solution is to seperate isr from calling jstUtilTimerInterruptHandler. For that we create a new task, which waits for a notification and after receiving one, calls the function in Espruino. Inside the isr we now have to send the notification. Sending a notification is done with vTaskNotifyGiveFromISR, a function of FREErtos. Waiting for the notification uses ulTaskNotifyTake, another function in FREErtos.

##Status## A first step with a simple waveform on an DAC port (GPIO25/GPIO26) runs without any crashes now. Thats good part of the answer, badly it does not change output :-( We are working on that......