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28 Intel 8255x 10/100 Mbps Ethernet Controller Family Open Source Software Developer Manual
Host Software Interface
The CBL consists of a linked list of individual action commands in structures called Command
Blocks (CBs). The CBs contain command parameters and status of the action commands. Action
commands are categorized as follows:
• Non-transmit (non-Tx) commands: This category includes commands such as no operation
(NOP), Configure, IA Setup, Multicast Setup, Dump and Diagnose.
• Transmit (Tx) command: This includes Transmit Command Blocks (TxCB).
The Receive Frame Area (RFA) consists of a list of Receive Frame Descriptors (RFDs) and a list of
user-prepared or NOS provided buffers. The receive architecture supports the simplified memory
model similar to the way it is supported by the transmit command. In the simplified memory
model, the data buffer immediately follows the RFD. The receive structures format and receive
code flow is described in Section 6.4.3.1, “Receive Frame Area” and Section 6.4.3.4, “No Buffer
Performance Improvements (82558 and 82559)”.
The LAN controller also provides read and write access to an external EEPROM and the
Management Data Interface (MDI) registers. This is achieved through the EEPROM Control
Register and the MDI Control Register, respectively. These registers occupy offsets 0Ch through
14h of the CSR.
Figure 8. 8255x Memory Architecture
10/100 Mbps Device (8255x) Registers
System Control
Block (SCB)
Buffer Descriptor Buffer Descriptor
Frame DescriptorFrame DescriptorFrame Descriptor
Control BlockControl BlockControl Block
Buffer Descriptor
Receive Data
Buffer
Receive Data
Buffer
Receive Data
Buffer
Command Block List (System Memory)
Receive Frame Area (System Memory)