S2_ADDMULTICASTADDRESS S2_MULTICAST S2_DELMULTICASTADDRESS S2_BROADCAST Some hardware supports broadcast and/or multicast. A broadcast is a packet sent to all other machines. A multicast is a packet sent to a set of machines. Drivers for hardware which does not allow broadcast or multicast will return ios2_Error S2ERR_NOT_SUPPORTED as appropriate. To send a broadcast, use S2_BROADCAST instead of CMD_WRITE. Broadcasts are received just like any other packets (using a CMD_READ for the appropriate packet type). To send a multicast, use S2_MULTICAST instead of CMD_WRITE. The device keeps a list of addresses that want to receive multicasts. You add a receiver's address to this list by using S2_ADDMULTICASTADDRESS. The receiver then posts a CMD_READ for the type of packet to be received. Some SANA-II devices which support multicast may have a limit on the number of addresses that can simultaneously wait for packets. Always check for an S2WERR_MULTICAST_FULL error return when adding a multicast address. Note that when the device adds a multicast address, it is usually added for all users of the device, not just the driver user which called S2_ADDMULTICASTADDRESS. In other words, received multicast packets will fill a read request of the appropriate type regardless of whether the requesting driver user is the same one which added the multicast address. In general, driver users should not care how received packets were sent (normally or broadcast/multicast), only that it was received. If a driver user really must know, however, it can check for SANA2IOB_BCAST and/or SANA2IOB_MCAST in the ios2_Flags field. Drivers should keep a count for the number of opens on a multicast address so that they don't actually remove it until it has been S2_DELMULTICASTADDRESS'd as many times as it has been S2_ADDMULTICASTADDRESS'd.
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