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82 Intel 8255x 10/100 Mbps Ethernet Controller Family Open Source Software Developer Manual
Host Software Interface
In the case of a port selective reset, the execution machine maintains configuration registers for the
device. In the case of a port software reset or a hardware reset, the device reverts to the default
values.
6.4.2.4 Multicast Setup (011b)
The multicast setup command is used for loading multicast IDs into the device for filtering
purposes. As previously noted, the filtering done on the multicast IDs is not perfect and some
unwanted frames may be accepted. This command resets the current filter and reloads it with the
specified multicast IDs. The format of the multicast addresses setup command is shown below.
Figure 18. Multicast Setup Command Format
Offset Command Word Bits 31:16 Status Word Bits 15:0
00h EL S I 0000000000 011 C X OK XXXXXXXXXXXXX
04h Link Address (A31:A0)
08h 2nd Byte 1st Byte X X Multicast Count
0Ch Multicast Address List
Nth Byte
Link Address
This is the 32-bit address of the next command block. It is added to the CU base to
obtain the actual address.
EL (Bit 31)
If this bit is set to one, it indicates that this command block is the last one on the CBL.
The CU will go from the active to the idle state after the execution of the CB is finished.
This transition will always cause an interrupt with the CNA/CI bit set in the SCB.
S (Bit 30)
If this bit is set to one, the CU will be suspended after the completion of this CB. A CNA
interrupt will be generated if the device is configured for this. The CU transitions from the
active to the suspended state after the execution of the CB.
I (Bit 29)
If the I bit is set to one, the device generates an interrupt after the execution of the CB is
finished. If I is not set to one, the CX interrupt will not be generated.
Bits 28:19 These bits are reserved and should all be set to 0.
CMD (Bits 18:16) This is the multicast setup command, which has a value of 011b.
C (Bit 15)
This bit indicates the execution status of the command. Software should reset this bit
before issuing the command to the device. Following a command completion, the device
sets it to one.
NOTE: The difference in the definition of the C bit for the transmit command
(Section 6.4.2.5).
OK (Bit 13)
The OK bit indicates that the command was executed without error. If it equals one, no
error occurred (command executed OK). If the OK bit is zero and the C bit is set, then an
error occurred.
NOTE: The difference in the definition of the C bit for the transmit command
(Section 6.4.2.5).
Multicast Count
This 14-bit field indicates the number of bytes in the multicast list field. The multicast
count must be a multiple of 6 bytes; otherwise, the device reduces the multicast count to
the nearest multiple of 6. If the multicast count equals 0, it resets the hash table, which is
equivalent to disabling the multicast filtering mechanism.
Multicast List
This field contains a list of multicast addresses or multiple IAs to be accepted by the
device. The least significant bit of the most significant byte of each multicast address
must equal 1.