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School of Computer Science & Engineering
University of New South Wales
 Advanced Operating Systems 
 COMP9242 2002/S2 

L4 IPC Messages

L4 IPC operations take two kinds of message parameters:

1. snd_reg or rcv_reg: in-register (``short'') part of message
   (first 8 words on MIPS R4k)
2. snd_msg or rcv_msg: in-memory (``long'') part of message

Messages consist of 3 kinds of data:

1. by-value in-line data (directly in registers or message buffer)
2. by-value ``string'' (out-of-line) data (message buffer contains pointer to data)
3. by-reference ``fpages'' (describing mappings)

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