CDK8920A View Datasheet(PDF) - Cirrus Logic
Part Name
Description
MFG CO.
'CDK8920A' PDF : 144 Pages View PDF
4.11.4 Basic Memory Mode Receive
Memory Mode receive operations occur in the
following order (interrupts used to signal the
presence of a valid receive frame):
1.A frame is received by the CS8920A, trigger-
ing an enabled interrupt.
2.The host reads the Interrupt Status Queue
(memory base + 0120h) and is informed of the
receive frame.
3.The host reads RxStatus (memory base +
0400h) to learn the status of the receive frame.
4.The host reads RxLength (memory base +
0402h) to learn the frame’s length.
5.The host reads the frame data by executing re-
petitive memory-to-memory move instructions
(REP MOVS) from memory base + 0404h to
transfer the entire frame from CS8920A mem-
ory to host memory.
For a more detailed description of receive, see
Section 5.2.
4.11.5 Polling the CS8920A in Memory Mode
If interrupts are not used, the host can poll the
CS8920A to check if receive frames are present
and if memory space is available for transmit.
However, this is beyond the scope of this data
sheet.
4.12 I/O Space Operation
In I/O Mode, PacketPage memory is accessed
through eight 16-bit I/O ports that are mapped
into 16 contiguous I/O locations in the host sys-
tem’s I/O space. I/O Mode is the default
configuration for the CS8920A and is always en-
CS8920A
abled. On power up, the default value of the I/O
base address is set at 300h. (Note that 300h is
typically assigned to LAN peripherals). The I/O
base address may be changed to any available
XXX0h location, either by loading configuration
data from the EEPROM, or during system setup.
Table 4.5 shows the CS8920A I/O Mode map-
ping:
Receive/Transmit Data Ports 0 and 1
These two ports are used when transferring trans-
mit data to the CS8920A and receive data from
the CS8920A. Port 0 is used for 16-bit opera-
tions and Ports 0 and 1 are used for 32-bit
operations (lower-order word in Port 0).
TxCMD Port
The host writes the Transmit Command
(TxCMD) to this port at the start of each trans-
mit operation. The Transmit Command tells the
CS8920A that the host has a frame to be trans-
mitted as well as how that frame should be
transmitted. This port is mapped into PacketPage
base + 0144h. See Register 9 in Section 4.4 for
more information.
TxLength Port
The length of the frame to be transmitted is writ-
ten here immediately after the Transmit
Offset
Type
Description
0000h Read/Write Receive/Transmit Data (Port 0)
0002h Read/Write Receive/Transmit Data (Port 1)
0004h Write-only TxCMD (Transmit Command)
0006h Write-only TxLength (Transmit Length)
0008h Read-only
Interrupt Status Queue
000Ah Read/Write
PacketPage Pointer
000Ch Read/Write PacketPage Data (Port 0)
000Eh Read/Write PacketPage Data (Port 1)
Table 4.5. I/O Mode Mapping
DS238PP2
83
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