Intel 82558 Manuale Utente

58

 

The format common to all action commands and the algorithms for beginning and completing the 

execution (also common to all action commands) is described below.

The general format of the Command Block (CB) includes the following fields:

An action command can be started by either the CU start or CU resume control command. 
Otherwise, it may follow a previous action command. However, the actual command start may be 

delayed by RU activity.

The following sequence is performed by the CU at the beginning of execution of each action 
command:

1. The device reads 4 Dwords of the CB in one continuous PCI burst (if possible).

2. The device analyzes the contents of the command word to determine the necessary action.

3. The device reads and analyzes the link offset of the next CB and saves it.

4. The device performs specific actions according to the action command specified in the current 

command field.

If the commands are chained, the CU prefetches the next command block by accessing the address 
specified in the link offset field of the current CB. The device reads, analyzes, and saves the 

command word of the next CB (the following fields are saved for later use: EL, S, I and CMD).

Command completion time is asynchronous to the beginning of the command. It is determined by 

the command type, RU activity, CU control commands, bus latency, etc. The CU is always in the 

active state at this time. The EL, S, and I bits determine the next actions.

100

Transmit

One transmit command is used to send a single frame. If more than one frame 
needs to be sent, the host CPU can link multiple transmit commands together.

101

Load Microcode

This command downloads microcode to the device.
Note: Documentation for microcode is beyond the scope of this manual.

110

Dump

This command causes the device to dump its internal registers into memory. 
The registers included are those loaded by the configure and address setup 
commands, plus status and other internal working registers.

111

Diagnose

The diagnose command puts the device CSMA/CD subsystem through a self-
test procedure and reports the result of the internal test.

00h

EL

S

I

0000000000

CMD

C

X

OK XXXXXXXXXXXXX

04h

Link Offset

08h

Optional Address and Data Fields