an example of a data envelope argument argo in the envelope stores the address in the dual port ram of the envelope 39 s data buffer the size of the buffer is specified at arg1 by specifying address and size of the data buffer in the envelope buffers of variable size and location can be used the crc field ensures correct retrieval of an envelope from the envelope queue to avoid hardware errors and or erroneous overriding of data buffers the dual port rams also enable efficient command protocols between each dsp and the mmi cpu 48 the command protocols are carried out in the cpu interface portion of dual port ram shown in fig7 referring to fig9 as the mmi writes a channel command word into the dual port ram it interrupts the dsp the dsp then reads the command and echoes it back using a command echo message to signal to the mmi cpu readiness for the next command word each command word to the dsp is tagged with an offset so that command is directed to a specific dsp offset pair for example 34 play gsm 3 34 includes the command 34 play gsm 34 and the offset 34 3 34 the dsp writes a status word to the mmi cpu to interrupt the mmi cpu indicating either normal or abnormal operation the envelope queue access protocol ensures that only one.