Analog Devices ADSP-SC58 Series Hardware Reference Manual page 691

Figure 15-10: Central Processor-Based Model
Figure 15-11: Link Port Full-Duplex Transfer Model
Figure 15-12: Link Port Ring Model
The link port protocol does not include built-in support for multiple masters. However, there can be situations
where multiple devices try to become the bus master at the same time. Multi-master conflicts can be resolved using
token passing. In token passing, the token is a software flag that passes between processors.
At reset, the token is set to reside in the link port of one device, making it the master and the transmitter. When a
receiver (slave) wants to become the master, it can assert its LP_ACK signal to get the attention of the master. The
master knows, through the software protocol, whether to respond with actual data or whether the token is requested.
If the master wishes to give up the token, it can send back a user-defined token release word and thereafter clear its
token flag.
Simultaneously, the slave sets its token and can thereafter transmit. The token release word can be any user-defined
value. Because the transmitter and receiver expect a code word, this word does not need to be exclusive of normal
ADSP-SC58x/ADSP-2158x SHARC+ Processor Hardware Reference
LP0
LP1
CENTRAL
PROCESSOR
LP2
LP3
LPx
PROCESSOR 1
LPy
PROCESSOR 1
LPx
LPx
PROCESSOR 4
LPy
LPx
PROCESSOR 3
PROCESSOR 1
PROCESSOR 2
PROCESSOR 3
PROCESSOR 4
LPx
PROCESSOR 2
LPy
LPy
LPx
PROCESSOR 2
LPy
LPy
Architectural Concepts
15–11