SAM4L Datasheet, PDF (845/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
31.6.2
Event Shaper (EVS) Operation
PEVC contains Event Shapers (EVS) for certain types of generators:
• External inputs
• General-purpose waveforms like timer outputs or Generic Clocks
Refer to the Module Configuration section at the end of this chapter for the device-specific con-
figuration of Event Shapers and Input Glitch Filters.
Each Event Shaper is responsible of shaping one input, prior to going through a PEVC channel:
• Optionally apply input-glich-filtering
• Synchronize incoming events
• Request CLK_PEVC when in deeper sleep modes
Write a one to the EN field of the corresponding Event Shaper Register (EVS) to enable
operation.
31.6.2.1
Input Glitch Filter (IGF)
Input Glitch Filtering can be turned on or off by writing to the Input Glitch Filter fields (IGFR and
IGFF) of the corresponding Event Shaper Register (EVS).
When IGF is on, the incoming event is sampled periodically. The sampling clock is divided from
CLK_RCSYS by the value of the Input Glitch Filter Divider Register (IGFDR). IGF will filter out
spikes and propagate only incoming events that respect one of the following two conditions:
• rise event: 2 samples low, followed by 0+ changes, followed by 2 samples high
• fall event: 2 samples high, followed by 0+ changes, followed by 2 samples low
CLK_RCSYS must be enabled to use Input Glitch Filtering.
31.6.3
Event Propagation Latency
Once a channel is setup, incoming peripheral events are relayed by hardware. Event progation
latency is therefore cycle deterministic. However, its value depends on the exact settings that
apply to a given channel.
When the channel multiplexer CHMXi.EVMX selects a generator without Event Shaper, event
propagation latency is 0 cycle. Software event is a particular case of 0 cycle propagation.
When the channel multiplexer CHMXi.EVMX selects a generator with Event Shaper, event prop-
agation latency depends on Input Glitch Filter setting EVSj.IGF and SleepWalking™:
• IGF off: event propagation latency is less or equal to 2 CLK_PEVC cycles
• IGF on: event propagation latency is less or equal to 3 * 2^IGFDR * CLK_RCSYS cycles
• in case of SleepWalking™ operation, an additional delay incurs if the PM needs to revive the
clocks sources. In that particular case of Low-Power operation, propagation latency is longer
and cannot be predicted.
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