
82801AA and 82801AB Datasheet
5-7
Functional Description
5.2.1.6
SYNC Time-out
There are several error cases that can occur on the LPC Interface.
Table 5-6
indicates the failing
case and the ICH response.
NOTE:
There may be other peripheral failure conditions; however, these are not handled by the ICH.
5.2.1.7
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 ICH was reading data from a peripheral, data is still transferred in the next two nibbles. This
data may be invalid, but it must be transferred by the peripheral. If the ICH was writing data to the
peripheral, the data had already been transferred.
In the case of multiple byte cycles, such as for memory and DMA cycles, an error SYNC
terminates the cycle. Therefore, if the ICH is transferring 4 bytes from a device, if the device
returns the error SYNC in the first byte, the other three bytes are not transferred.
Upon recognizing the SYNC field indicating an error, the ICH treats this the same as IOCHK#
going active on the ISA bus.
5.2.1.8
LFRAME# Usage
Start of Cycle
For Memory, I/O, and DMA cycles, the ICH asserts LFRAME# for 1 clock at the beginning of the
cycle (
Figure 5-5
) During that clock, the ICH drives LAD[3:0] with the proper START field.
Table 5-6. ICH Response to Sync Failures
Possible Sync Failure
ICH Response
ICH 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.
ICH aborts the cycle after
the 4
clock.
ICH drives a Memory, I/O, or DMA cycle, and a peripheral drives more than 8
consecutive valid SYNC to insert wait states using the Short (‘0101b’) encoding
for SYNC. This could occur if the peripheral is not operating properly.
Continues waiting
ICH 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.
ICH aborts the cycle when
the invalid Sync is
recognized.