19.6 Special Bus Granting Mechanism

The MATRIX provides some speculative bus granting techniques in order to anticipate access requests from hosts. This mechanism reduces latency at first access of a burst, or for a single transfer, as long as the client is free from any other host access. It does not provide any benefit if the client is continuously accessed by more than one host, since arbitration is pipelined and has no negative effect on the client bandwidth or access latency.

This bus granting mechanism sets a different default host for every client.

At the end of the current access, if no other request is pending, the client remains connected to its associated default host. A client can be associated with three kinds of default hosts:

• No default host
• Last access host
• Fixed default host

To change from one type of default host to another, the user interface provides Client Configuration registers (MATRIX_SCFGx), one for every client, which set a default host for each client. MATRIX_SCFGx contains two fields to manage host selection: DEFMSTR_TYPE and FIXED_DEFMSTR. The 2-bit DEFMSTR_TYPE field selects the default host type (no default, last access host, fixed default host), whereas the 4-bit FIXED_DEFMSTR field selects a fixed default host provided that DEFMSTR_TYPE is set to fixed default host. See Bus Matrix Client Configuration Registers.