Dram; Expander Buses; Pci Buses; Agp - Intel 460GX Software Developer’s Manual

Data Integrity and Error Handling
6.1.2

DRAM

•
The 460GX chipset provides ECC generation on all writes into the DRAM, and ECC checking
on all reads from the DRAM. Single-bit errors are corrected. Multi-bit errors will return
poisoned data. Both types of errors are logged, with the address and ECC bits for the data
being recorded. The row which failed, as well as the bit for single-bit errors, can be identified
by software.
•
The first instance of a single-bit error is logged. After the first error, additional status flags
indicate subsequent errors occurred. The first multi-bit error is logged, with a status bit
indicating there were more uncorrectable errors. In both cases, software can clear the error
register and reset the error capture logic.
•
Single-bit errors are corrected as they are received.
•
To facilitate component debug and diagnostics, the ECC code generated on writes into the
DRAM can be forced incorrect. A configuration bit, when set, will force the ECC bits that are
written into memory to be XOR'ed with the correct value. This will allow either single or
double bit failures to be generated in memory. When the data is read, the system should correct
the data and report the error for single-bit errors, or report the error for double bit errors while
passing bad ECC to the processor.
6.1.3

Expander Buses

•
Parity bits are generated and checked independently for each Expander bus. For error behavior
see Table
•
Hard Fail responses are supported.
•
A mechanism for elevating fatal errors to BINIT# (XBINIT#) and non-fatal errors to BERR#
(XBERR#) is provided.
6.1.4

PCI Buses

•
Parity bits are generated and checked independently for each PCI bus.
•
Standard PCI checking for aborts, PERR# and SERR# are also done.
6.1.5

AGP

•
There is no parity on the bus between the graphics card and the GXB when using AGP
protocol. Transactions using PCI protocol have parity as defined for the standard PCI bus.
•
The GXB checks for illegal or unknown operations, Expander bus parity errors, or internal
parity errors.
•
There is parity on the GART table.
6.1.6

Private Bus between SAC and SDC

•
There will be parity on the 64 bit data bus. Errors on data into the SDC will poison the data in
the DB. Errors on data into the SAC will always be passed on without correction, with an
option to BINIT#.
•
The command bus and ITID bus are parity protected. Parity errors on this bus cause a BINIT#.
6-2
6-1.
Intel® 460GX Chipset Software Developer's Manual