Functional Description
5-22
Intel
82801BA ICH2 Datasheet
5.3.1.6
SYNC Time-out
There are several error cases that can occur on the LPC interface.
Table 5-9
indicates the failing
case and the ICH2 response.
NOTE:
There may be other peripheral failure conditions; however, these are not handled by the ICH2.
5.3.1.7
SYNC Error Indication
The SYNC protocol allows the peripheral to report an error via the LAD[3:0] = 1010b encoding.
The intent of this encoding is to give peripherals a method of communicating errors to aid higher
layers with more robust error recovery.
If the ICH2 was reading data from a peripheral, data will still be transferred in the next two nibbles.
This data may be invalid; however, it must be transferred by the peripheral. If the ICH2 was
writing data to the peripheral, the data had already been transferred.
In the case of multiple byte cycles (e.g., for memory and DMA cycles) an error SYNC terminates
the cycle. Therefore, if the ICH2 is transferring 4 bytes from a device and the device returns the
error SYNC in the first byte, the other three bytes are not transferred.
When recognizing the SYNC field indicating an error, the ICH2 treats this the same as IOCHK#
going active on the ISA bus.
5.3.1.8
LFRAME# Usage
Start of Cycle
For Memory, I/O, and DMA cycles, the ICH2 asserts LFRAME# for 1 clock at the beginning of the
cycle (
Figure 5-7
) During that clock, the ICH2 drives LAD[3:0] with the proper START field.
Table 5-9. ICH2 Response to Sync Failures
Possible Sync Failure
ICH2 Response
ICH2 starts a Memory, I/O, or DMA cycle, but no device drives a valid SYNC
after 4 consecutive clocks. This could occur if the processor tries to access an
I/O location to which no device is mapped.
ICH2 aborts the cycle after
the 4
clock.
ICH2 drives a Memory, I/O, or DMA cycle, and a peripheral drives more than 8
consecutive valid SYNC patterns to insert wait states using the Short (‘0101b’)
encoding for SYNC. This could occur if the peripheral is not operating properly.
Continues waiting
ICH2 starts a Memory, I/O, or DMA cycle, and a peripheral drives an invalid
SYNC pattern. This could occur if the peripheral is not operating properly or if
there is excessive noise on the LPC interface.
ICH2 aborts the cycle when
the invalid Sync is
recognized.
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