MEC1322 Datasheet, PDF (86/456 Pages) Microchip Technology – Keyboard and Embedded Controller for Notebook PC

MEC1322
The Sample phase for each IRQ/Data follows the low to high transition of the Start Frame pulse by a number of clocks
equal to the IRQ/Data Frame times three, minus one e.g. The IRQ5 Sample clock is the sixth IRQ/Data Frame, then the
sample phase is {(6 x 3) - 1 = 17} the seventeenth clock after the rising edge of the Start Pulse.
TABLE 5-11: SERIRQ SAMPLING PERIODS
SERIRQ Period
Signal Sampled
1
Not Used
2
IRQ1
3
IRQ2
4
IRQ3
5
IRQ4
6
IRQ5
7
IRQ6
8
IRQ7
9
IRQ8
10
IRQ9
11
IRQ10
12
IRQ11
13
IRQ12
14
IRQ13
15
IRQ14
16
IRQ15
# of Clocks Past Start
2
5
8
11
14
17
20
23
26
29
32
35
38
41
44
47
The SIRQ data frame will now support IRQ2 from a logical device; previously SERIRQ Period 3 was reserved for use
by the System Management Interrupt (LSMI#). When using Period 3 for IRQ2, the user should mask off the SMI via the
ESMI Mask Register. Likewise, when using Period 3 for LSMI#, the user should not configure any logical devices as
using IRQ2.
SERIRQ Period 14 is used to transfer IRQ13. Each Logical devices will have IRQ13 as a choice for their primary inter-
rupt.
STOP CYCLE CONTROL
Once all IRQ/Data Frames have completed, the host controller will terminate SERIRQ activity by initiating a Stop Frame.
Only the host controller can initiate the Stop Frame. A Stop Frame is indicated when the SERIRQ is low for two or three
clocks. If the Stop Frame’s low time is two clocks, then the next SERIRQ cycle’s sampled mode is the Quiet mode; and
any SERIRQ device may initiate a Start Frame in the second clock or more after the rising edge of the Stop Frame’s
pulse. If the Stop Frame’s low time is three clocks, then the next SERIRQ cycle’s sampled mode is the continuous mode,
and only the host controller may initiate a Start Frame in the second clock or more after the rising edge of the Stop
Frame’s pulse.
5.8.4.4 Latency
Latency for IRQ/Data updates over the SERIRQ bus in bridge-less systems with the minimum IRQ/Data Frames of 17
will range up to 96 clocks (3.84μS with a 25 MHz LCLK or 2.88μs with a 33 MHz LCLK).
Note:
If one or more PCI to PCI Bridge is added to a system, the latency for IRQ/Data updates from the secondary
or tertiary buses will be a few clocks longer for synchronous buses, and approximately double for asyn-
chronous buses.
5.8.4.5 EOI/ISR Read Latency
Any serialized IRQ scheme has a potential implementation issue related to IRQ latency. IRQ latency could cause an
EOI or ISR Read to precede an IRQ transition that it should have followed. This could cause a system fault. The host
interrupt controller is responsible for ensuring that these latency issues are mitigated. The recommended solution is to
delay EOIs and ISR Reads to the interrupt controller by the same amount as the SERIRQ Cycle latency in order to
ensure that these events do not occur out of order.
DS00001719D-page 86
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