Datasheet

ACPI Devices
Intel
®
Atom™ Processor E6xx Series Datasheet
228
• Start Frame: SERIRQ line driven low by the interrupt controller to indicate the
start of IRQ transmission
• Data Frames: IRQ information transmitted by peripherals. The interrupt controller
supports 21 data frames.
• Stop Frame: SERIRQ line driven low by the interrupt controller to indicate end of
transmission and next mode of operation.
11.5.2 Start Frame
The serial IRQ protocol has two modes of operation which affect the start frame:
• Continuous Mode: The interrupt controller is solely responsible for generating the
start frame
• Quiet Mode: Peripheral initiates the start frame, and the interrupt controller
completes it.
These modes are entered via the length of the stop frame.
Continuous mode must be entered first, to start the first frame. This start frame width
is 8 LPC clocks. This is a polling mode.
In Quiet mode, the SERIRQ line remains inactive and pulled up between the Stop and
Start Frame until a peripheral drives SERIRQ low. The interrupt controller senses the
line low and drives it low for the remainder of the Start Frame. Since the first LPC clock
of the start frame was driven by the peripheral, the interrupt controller drives SERIRQ
low for 1 LPC clock less than in continuous mode. This mode of operation allows for
lower power operation.
11.5.3 Data Frames
Once the Start frame has been initiated, the SERIRQ peripherals 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, a device drives SERIRQ low if its corresponding
interrupt signal is low. If its corresponding interrupt is high, then the SERIRQ
devices tristate SERIRQ. SERIRQ remains high due to pull-up resistors.
• Recovery Phase: During this phase, a device drives SERIRQ high if it was driven
low during the Sample Phase. If it was not driven during the sample phase, it
remains tristated in this phase.
• Turn-around Phase: The device tristates SERIRQ.
11.5.4 Stop Frame
After the data frames, a Stop Frame will be driven by the interrupt controller. SERIRQ
will be driven low for 2 or 3 LPC clocks. The number of clocks is determined by the
SCNT.MD field in D31:F0 configuration space. The number of clocks determines the
next mode:
Table 332. Serial Interrupt Mode Selection
Stop Frame Width Next Mode
2 LPC clocks Quiet Mode: Any SERIRQ device initiates a Start Frame
3 LPC clocks Continuous Mode: Only the interrupt controller initiates a Start Frame