Can anyone provide some information or a code snippet to implement a glitch filter for E70 or Cortex-M if possible using ASF ? I see that there are several PIO registers and there is an ASF function pio_set_debounce_filter() but I cannot figure out how to calculate appropriate values to filter noise on the interrupt pin.
EDIT: added debounce filter configuration in working title
I tested glitch and debounce filter configurations and failed to configure a "pure" debounce filter. I have an interrupt service routine which must be triggered with the first edge of a transition and shall ignore following transitions for a couple of microseconds. Checking out the glitch and debounce timings shown in the E70 manual I did not find a signal which matches what I call a debounce filter. The red colored signal behavior is what I need/expected:
If I set up a filter using PIO_IFCSR=1 and PIO_IFSR=0 no filtering seems to apply. If PIO_IFSR=1 is set then the interrupt is delayed and glitches are removed.
I checked out the ASF source of the ioport setup and it seems to me that a pure debounce filter cannot be configured at least using ASF. The code below is executed when calling ioport_set_pin_input_mode().
__always_inline static void arch_ioport_set_port_mode(ioport_port_t port,
ioport_port_mask_t mask, ioport_mode_t mode)
:
if (mode & (IOPORT_MODE_GLITCH_FILTER | IOPORT_MODE_DEBOUNCE)) {
base->PIO_IFER = mask;
} else {
base->PIO_IFDR = mask;
}
:So it seems it is not possible to configure a debounce filter without filtering glitches too and having a significant delay ?
This is the code I use for debounce filter configuration:
#define MAX_FILTER_FREQ 32768/2 #define SLOW_CLOCK_FREQ MAX_FILTER_FREQ #define PIN_NOT_INT_GPIO (PIO_PA3_IDX) #define IOPORT_MODE (IOPORT_MODE_DEBOUNCE) #define PIO_MODE (PIO_DEBOUNCE) #define PIN_NOT_INT_FLAGS (IOPORT_MODE_PULLUP | IOPORT_MODE) #define PIN_NOT_INT_SENSE (IOPORT_SENSE_RISING) #define PIN_NOT_INT_MASK PIO_PA3 #define PIN_NOT_INT_PIO PIOA #define PIN_NOT_INT_ID ID_PIOA ioport_set_pin_input_mode(PIN_NOT_INT_GPIO, PIN_NOT_INT_FLAGS, IOPORT_MODE); pio_set_debounce_filter(PIN_NOT_INT_PIO, PIN_NOT_INT_MASK, SLOW_CLOCK_FREQ); pio_handler_set(PIN_NOT_INT_PIO, PIN_NOT_INT_ID, PIN_NOT_INT_MASK, PIN_NOT_INT_ATTR, PeakIrq); pio_handler_set_priority(PIN_NOT_INT_PIO, (IRQn_Type) PIN_NOT_INT_ID, IRQ_PRIOR_PEAK_CURR); pio_enable_interrupt(PIN_NOT_INT_PIO, PIN_NOT_INT_MASK);
Jack Ganssle wrote a pretty good article about software debouncing here: https://www.embedded.com/electro...
The trick is to shift the edges through a variable of whatever size you want. Use interrupts and a timer to trigger/sample the signal at whatever frequency you want. Once the edges make it all the way through the variable has a bit value of all ones, and the signal is active. All zeros and the signal is inactive. But anything else is a transition state for you to handle however you want.
In your case sample quickly and drop short strings on one's as noise. But accept longer strings of one's as a valid transition. Or go even more complicated and only debounce the first transition, then accept all edges. Again, all done in software.
