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3.0 Functional Description
3.7 PCI Bus Interface
Bt8230
ATM Segmentation and Reassembly Controller—SAR
N8230DS1F
it reaches the value set in the MAX_BUR_LEN field of the PCI configuration
space, the burst is terminated and a new address phase is begun.
It is possible for the addressed slave to request a disconnect or a retry during a
read or a write transfer, using the defined PCI protocol sequence. In this case, the
bus master logic will terminate the current burst, maintain its bus request, and
restart the transfer at the point of termination. Disconnects and retries are not
regarded as errors.
Five possible sources of error are present during any PCI bus master transac-
tion. If any of the following five errors occur, the bus master logic will perma-
nently terminate the transaction, flag an error, and cease to process any more
commands until either the corresponding status flag in the PCI configuration
space has been cleared or the PCI master has been reset.
1
Target Abort—The PCI transaction will terminate if the addressed target
signals a target abort. In this case, the RTA and MERROR bits in the PCI
Configuration Register space will be set and the PCI_BUS_STATUS[4] bit
in the SYS_STAT register will be set.
2
Master Abort—If the addressed target does not respond with an
HDEVSEL* assertion, then a master abort is flagged. In this case, the
RMA and MERROR bits in the PCI Configuration Register space will be
set and the PCI_BUS_STATUS[3] bit in the SYS_STAT register will be
set.
3
Parity Error—If the data parity checked during read transfers is inconsis-
tent with the state of the HPAR signal, then a parity error is signaled. In
this case, the DPR and MERROR bits in the PCI Configuration Register
space will be set and the PCI_BUS_STATUS[2] bit in the SYS_STAT reg-
ister will be set.
4
Interface Disabled—If the driver or application software on the PCI host
CPU has disabled the Bt8230 PCI bus master logic (using the M_EN bit in
the Command field of the PCI bus configuration registers), then any
attempt to perform a DMA transaction to the PCI bus will result in an
error. In this case, the MERROR and INTF_DIS bits in the PCI configura-
tion space will be set and the PCI_BUS_STATUS[1] bit in the SYS_STAT
register will be set.
5
Internal Failure—Upon a synchronization error between the DMA copro-
cessor and the PCI master logic, an internal failure will be flagged. In this
case, the MERROR and INT_FAIL bits in the PCI configuration space will
be set and the PCI_BUS_STATUS[0] bit in the SYS_STAT register will be
set.
As mentioned above, bus protocol errors can be cleared either by a software
reset of the associated status flag or flags; i.e., RTA, RMA or DPR, or with a reset
of the PCI bus master logic using the HRST* input pin. For example, a master
abort error can be cleared by writing a logic one to the RMA status bit in the PCI
Configuration Register space, causing the status bit to be cleared and the master
to resume normal operation. The MERROR bit in the PCI Configuration Register
drives the PCI_BUS_ERROR interrupt. To clear this interrupt, a logic high must
be written to the MERROR bit location. The MERROR bit can also be cleared by
a logic low on the HRST* input pin.
Several fields are provided in the PCI configuration space to aid in recovering
from a PCI master error. The PCI host software can determine that an error
occurred by checking the MERROR bit. It also can determine if the transaction