SAM4L Datasheet, PDF (540/1185 Pages) ATMEL Corporation – ATSAM ARM-based Flash MCU

ATSAM4L4/L2
23.6.2.8
tion of 2 CLK_GPIO cycles or more is accepted. For pulse durations between 1 and 2
CLK_GPIO cycles, the pulse may or may not be taken into account, depending on the precise
timing of its occurrence. Thus for a pulse to be guaranteed visible it must exceed 2 CLK_GPIO
cycles, whereas for a glitch to be reliably filtered out, its duration must not exceed 1 CLK_GPIO
cycle. The filter introduces 2 clock cycles latency.
The glitch filters are controlled by the Glitch Filter Enable Register (GFER). When a bit in GFER
is one, the glitch filter on the corresponding pin is enabled. The glitch filter affects only interrupt
inputs. Inputs to peripherals or the value read through PVR are not affected by the glitch filters.
Interrupt Timings
Figure 23-4 shows the timing for rising edge (or pin-change) interrupts when the glitch filter is
disabled. For the pulse to be registered, it must be sampled at the rising edge of the clock. In this
example, this is not the case for the first pulse. The second pulse is sampled on a rising edge
and will trigger an interrupt request.
Figure 23-4. Interrupt Timing with Glitch Filter Disabled
CLK_GPIO
Pin Level
IFR
Figure 23-5 shows the timing for rising edge (or pin-change) interrupts when the glitch filter is
enabled. For the pulse to be registered, it must be sampled on two subsequent rising edges. In
the example, the first pulse is rejected while the second pulse is accepted and causes an inter-
rupt request.
Figure 23-5. Interrupt Timing with Glitch Filter Enabled
CLK_GPIO
Pin Level
IFR
23.6.2.9
CPU Local Bus
The CPU Local Bus can be used for application where low latency read and write access to the
Output Value Register (OVR) and Output Drive Enable Register (ODER) is required. The CPU
Local Bus allows the CPU to configure the mentioned GPIO registers directly, bypassing the
shared Peripheral Bus (PB).
To avoid data loss when using the CPU Local Bus, the CLK_GPIO must run at the same fre-
quency as the CLK_CPU. See Section 23.5.2 for details.
The CPU Local Bus is mapped to a different base address than the GPIO but the OVER and
ODER offsets are the same. See the CPU Local Bus Mapping section in the Memories chapter
for details.
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