RM0046 eTimer
Doc ID 16912 Rev 5 725/936
Input Filter Register (FILT)
Input filter considerations
The FILT_PER value should be set such that the sampling period is larger the period of the
expected noise. This way a noise spike will only corrupt one sample. The FILT_CNT value
should be chosen to reduce the probability of noisy samples causing an incorrect transition
to be recognized. The probability of an incorrect transition is defined as the probability of an
incorrect sample raised to the FILT_CNT + 3 power.
The values of FILT_PER and FILT_CNT must also be traded off against the desire for
minimal latency in recognizing input transitions. Turning on the input filter (setting FILT_PER
to a non-zero value) introduces a latency of:
{[(FILT_CNT + 3) × FILT_PER] +2} IPBus
clock periods.
26.6.3 Watchdog timer registers
The base address of the Watchdog Timer registers is equal to the base address of the
eTimer plus an offset of 0x100.
Figure 407. Input Filter register (FILT)
Address:
Base + 0x001E (eTimer0)
Base + 0x003E (eTimer1)
Base + 0x005E (eTimer2)
Base + 0x007E (eTimer3)
Base + 0x009E (eTimer4)
Base + 0x00BE (eTimer5)
Access: User read/write
0123456789101112131415
R00000
FILT_CNT[2:0] FILT_PER[7:0]
W
Reset0000000000000000
Table 381. FILT field descriptions
Field Description
FILT_CNT[2:0]
Input Filter Sample Count
These bits represent the number of consecutive samples that must agree prior to the input filter
accepting an input transition. A value of 0 represents 3 samples. A value of 7 represents 10
samples. The value of FILT_CNT affects the input latency as described in Section , “Input filter
considerations.
FILT_PER[7:0]
Input Filter Sample Period
These bits represent the sampling period (in IPBus clock cycles) of the eTimer input signal. Each
input is sampled multiple times at the rate specified by FILT_PER. If FILT_PER is 0x00 (default),
then the input filter is bypassed. The value of FILT_PER affects the input latency as described in
Section , “Input filter considerations.
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