Data Frames; Stop Frame; Specific Interrupts Not Supported Using Serirq; Stop Frame Explanation - Intel 6 SERIES CHIPSET - DATASHEET 01-2011 Datasheet

Functional Description
5.10.2

Data Frames

Once the Start frame has been initiated, all of the SERIRQ peripherals must start
counting frames based on the rising edge of SERIRQ. Each of the IRQ/DATA frames has
exactly 3 phases of 1 clock each:
• Sample Phase. During this phase, the SERIRQ device drives SERIRQ low if the
corresponding interrupt signal is low. If the corresponding interrupt is high, then
the SERIRQ devices tri-state the SERIRQ signal. The SERIRQ line remains high due
to pull-up resistors (there is no internal pull-up resistor on this signal, an external
pull-up resistor is required). A low level during the IRQ0–1 and IRQ2–15 frames
indicates that an active-high ISA interrupt is not being requested, but a low level
during the PCI INT[A:D], SMI#, and IOCHK# frame indicates that an active-low
interrupt is being requested.
• Recovery Phase. During this phase, the device drives the SERIRQ line high if in
the Sample Phase it was driven low. If it was not driven in the sample phase, it is
tri-stated in this phase.
• Turn-around Phase. The device tri-states the SERIRQ line
5.10.3

Stop Frame

After all data frames, a Stop Frame is driven by the PCH. The SERIRQ signal is driven
low by the PCH for 2 or 3 PCI clocks. The number of clocks is determined by the
SERIRQ configuration register. The number of clocks determines the next mode.
Table 5-19. Stop Frame Explanation
Stop Frame Width
2 PCI clocks
3 PCI clocks
5.10.4

Specific Interrupts Not Supported Using SERIRQ

There are three interrupts seen through the serial stream that are not supported by the
PCH. These interrupts are generated internally, and are not sharable with other devices
within the system. These interrupts are:
• IRQ0. Heartbeat interrupt generated off of the internal 8254 counter 0.
• IRQ8#. RTC interrupt can only be generated internally.
• IRQ13. Floating point error interrupt generated off of the processor assertion of
FERR#.
The PCH ignores the state of these interrupts in the serial stream, and does not adjust
their level based on the level seen in the serial stream.
Datasheet
Quiet Mode. Any SERIRQ device may initiate a Start Frame
Continuous Mode. Only the host (the PCH) may initiate a Start Frame
Next Mode
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