User Manual
BCM1250/BCM1125/BCM1125H
10/21/02
B r o a d c o m C o r p o r a t i o n
Document
1250_1125-UM100CB-R
Section 3: System Overview
Page
25
If an error is signalled during a data transfer the system takes care to maintain the error condition. If bad data
is sent to the L2 cache or memory controller an uncorrectable ECC pattern is written with the data, so that
subsequent reads will also see an error and bad data will not be used in processing. This can lead to a cascade
of errors during the period between the initial detection of an error and software recovery code running (the
SCD error log will record the first problem).
The D_MOD signal is asserted if the data being transferred is dirty (i.e. differs from L2/memory). In this case
the L2 cache or memory controller will take a copy of the data, so that the new owner receives it clean.
The memory controller and L2 cache work together to supply data for any of the memory regions of the address
space.
shows the decision process that is used on reads and writes to the memory region to
determine which agent supplies the data and which accepts write data. It also shows which of the memory or
L2 will write back data when dirty data is supplied by an exclusive owner.
100
Bus error. A CPU will take a bus error exception
if it receives this error.
I/O bridge0: PCI parity error, master or target
abort. HyperTransport NxA or error return.
I/O bridge1: Generic bus error (no chip select for
the address, time-out during an access or I/O bus
parity error).
Memory Controller: No chip select decoded for
the address.
SCD: The SCD will return this error with
UNPREDICTABLE data if the bus watcher
detects an illegal address.
101
Fatal bus error. The ownership of the block is
unclear. This can be caused by a CPU tag parity
error, or because software used a CACHEOP to
invalidate an exclusive line and the CPU had
committed to supply the line in the window while
the operation executed. A CPU will take a bus
error exception if it receives this error.
Memory Controller: The memory controller
returns UNPREDICTABLE data with this error
code if an agent asserts both R_SHD and
R_EXC.
I/O bridge1: This error code is returned with
UNPREDICTABLE data and the io_coh_err bit
will be set if some agent asserts both R_SHD and
R_EXC during a coherent generic bus access.
110
Uncorrectable ECC error in the tag. A CPU will
take a cache error exception if it receives this
error.
CPU: Tag parity error.
L2 Cache: Tag ECC error.
111
Uncorrectable ECC error in the data (L2 cache
or memory controller). A CPU will take a cache
error exception if it receives this error.
CPU: Data cache had uncorrectable data ECC
error.
Memory Controller: Data ECC error.
L2 Cache: Data ECC error
I/O bridge: Write of a Read-modify-write
operation that received an uncorrectable data
error during the read.
Table 6: ZBbus Data Status Codes
(Cont.)
D_CODE[2:0]
Status of Data on D_DA
Sources of Error