am79c972b Advanced Micro Devices, am79c972b Datasheet - Page 43

• Manufacturer Part Number: am79c972b
• Description: Pcnet?-fast+ Enhanced 10/100 Mbps Pci Ethernet Controller With Onnow Support
• Manufacturer: Advanced Micro Devices

Whenever the Am79C972 controller is the current bus
master and a data parity error occurs, SINT (CSR5, bit
11) will be set to 1. When SINT is set, INTA is asserted
if the enable bit SINTE (CSR5, bit 10) is set to 1. This
mechanism can be used to inform the driver of the sys-
tem error. The host can read the PCI Status register to
determine the exact cause of the interrupt. The setting
of SINT due to a data parity error is not dependent on
the setting of PERREN (PCI Command register, bit 6).
By default, a data parity error does not affect the state
of the MAC engine. The Am79C972 controller treats the
data in all bus master transfers that have a parity error
as if nothing has happened. All network activity contin-
ues.
Advanced Parity Error Handling
For all DMA cycles, the Am79C972 controller provides
a second, more advanced level of parity error handling.
This mode is enabled by setting APERREN (BCR20, bit
10) to 1. When APERREN is set to 1, the BPE bits
(RMD1 and TMD1, bit 23) are used to indicate parity
error in data transfers to the receive and transmit buff-
ers. Note that since the advanced parity error handling
uses an additional bit in the descriptor, SWSTYLE
(BCR20, bits 7-0) must be set to 2 or 3 to program the
Am79C972 controller to use 32-bit software structures.
The Am79C972 controller will react in the following way
when a data parity error occurs:
n Initialization block read: STOP (CSR0, bit 2) is set to
n Descriptor ring read: Any on-going network activity
n Descriptor ring write: Any on-going network activity
n Transmit buffer read: BPE (TMD1, bit 23) is set in
n Receive buffer write: BPE (RMD1, bit 23) is set in
Terminating on-going network transmission in an or-
derly sequence means that if less than 512 bits have
been transmitted onto the network, the transmission
1 and causes a STOP_RESET of the device.
is terminated in an orderly sequence and then STOP
(CSR0, bit 2) is set to 1 to cause a STOP_RESET
of the device.
is terminated in an orderly sequence and then STOP
(CSR0, bit 2) is set to 1 to cause a STOP_RESET
of the device.
the current transmit descriptor. Any on-going net-
work transmission is terminated in an orderly se-
quence.
the last receive descriptor associated with the frame.
Am79C972
will be terminated immediately, generating a runt
packet.
If 512 bits or more have been transmitted, the message
will have the current FCS inverted and appended at the
next byte boundary to guarantee an FCS error is de-
tected at the receiving station.
APERREN does not affect the reporting of address
parity errors or data parity errors that occur when the
Am79C972 controller is the target of the transfer.
Initialization Block DMA Transfers
During execution of the Am79C972 controller bus mas-
ter initialization procedure, the Am79C972 microcode
will repeatedly request DMA transfers from the BIU.
During each of these initialization block DMA transfers,
the BIU will perform two data transfer cycles reading
one DWord per transfer and then it will relinquish the
bus. When SSIZE32 (BCR20, bit 8) is set to 1 (i.e., the
initialization block is organized as 32-bit software struc-
tures), there are seven DWords to transfer during the
bus master initialization procedure, so four bus master-
ship periods are needed in order to complete the initial-
ization sequence. Note that the last DWord transfer of
the last bus mastership period of the initialization se-
quence accesses an unneeded location. Data from this
transfer is discarded internally. When SSIZE32 is
cleared to 0 (i.e., the initialization block is organized as
16-bit software structures), then three bus mastership
periods are needed to complete the initialization se-
quence.
The Am79C972 supports two transfer modes for read-
ing the initialization block: non-burst and burst mode,
with burst mode being the preferred mode when the
Am79C972 controller is used in a PCI bus application.
See Figure 23 and Figure 24.
When BREADE is cleared to 0 (BCR18, bit 6), all initial-
ization block read transfers will be executed in non-
burst mode. There is a new address phase for every
data phase. FRAME will be dropped between the two
transfers. The two phases within a bus mastership pe-
riod will have addresses of ascending contiguous or-
der.
When BREADE is set to 1 (BCR18, bit 6), all initializa-
tion block read transfers will be executed in burst mode.
AD[1:0] will be 0 during the address phase indicating a
linear burst order.
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