IPC@CHIP Documentation - SC12 @CHIP-RTOS V1.10

CX
Number of data structures in array at [BX:SI]. Up to this number of device interfaces will be reported.
Return Value
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DX = 0, the user provided array at [BX:SI] contains the current device interface information
AX = Number of entries reported in array at [BX:SI].
Interrupt 0xAC service 0x90: ADD_IGMP_MEMBERSHIP, Install an IP multicast address entry
Parameters
AH
ES:DI
DS:SI
Install an IP multicast address entry to become a member of an IP multicast group.
0x90 (= ADD_IGMP_MEMBERSHIP)
Pointer to multicast IP address of type unsigned long
Pointer to a 6 byte array that contains the corresponded Ethernet address
Return Value
Comments
DX = 0, AX = 0: Success
DX = -1: AX contains error code, invalid class D address, or no free entry in IGMP table available
IP Multicasting is the Internet abstraction of hardware multicasting. It allows transmission of IP datagrams to a
group of hosts that form a single multicast group. Membership in a multicast group is dynamic. Hosts may
join or leave the group at any time. Each multicast group has unique IP multicast address (Class D address).
The first four bits of an IP multicast address must match to binary 1110. IP multicast addresses range from
224.0.0.0 through 239.255.255.255.
For the usage of IP multicasting on an Ethernet interface, IP multicast addresses must be mapped to Ethernet
hardware addresses. The Ethernet device of the IPC@CHIP will be switched into the Ethernet multicast
mode. In this mode it receives any incoming IP packet with the mapped Ethernet multicast address and
forwards it to the TCP/IP layer. Each IP multicast packet will be sent with the mapped Ethernet multicast
address.
Because of the feature, that a multicast IP packet will be received by any member of a multicast group, sending
and receiving of IP multicast packets is only usable with UDP sockets (datagram sockets).
After installing a IP multicast address with this API, the application programmer is able use this address as a
destination address when sending datagrams. A UDP socket is able to receive datagrams at the specified
multicast address.
The maximum number of supported IP multicast addresses in the IPC@CHIP is limited to 15. Before installing
an IP multicast address, you can find out the corresponding Ethernet multicast address with Map IP multicast
address to Ethernet address API.
Using multicast addresses is only possible on the Ethernet interface.
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