0. bus arbitration
AHB is not provided for arbitration algorithm arbiter, it can be based on different applications, take a different arbitration mechanism. Such uses fixed priority arbitration (Fixed priority), circulating priority arbitration (Round Robin), random or arbitration (the Random) and competition arbitration priority level (Tournament) and the like.
Robin priority: the priority level of each master no difference, they will in turn get access to the bus, in order to avoid the disadvantage of a low-priority master might be indefinitely latched.
1. Arbitration Process
1.1 Ordinary Arbitration
The desired master acquired the bus arbiter asserting a bus request signal to the arbitration, the arbiter via arbitration according to the arbitration logic, the bus response signal sent HGRANT. Master is sampled on the rising edge of the clock signal HGRANT, when sampled HGRANT effective, and at the same time HREADY is high, indicating that the bus master granted access and may begin transmitting.
1.2 master lock arbitration
If you get access to the bus master does not want to be interrupted during transmission , and want continuous non-interrupted transmission, then the master at the same time issuing a bus request signal (HBUSREQ) can issue bus latch signal HLOCK , soon HLOCK set high.
When the master gains bus access arbiter will send a corresponding response signal HMASTLOCK, so arbiter will not be released to the other bus master, until the master itself HLOCK cancel latch signal is set low, the arbiter will bus arbitration operation, the master can be performed so that other bus operation. Here we assume that burst priority fixed length of transmission are not interrupted.
1.3 SPLIT transmission
Arbitration can also hope to complete the arbitration bus slave SPLIT transmission. When the master arbiter observed claimed SPLIT response is received, the master priority will be shielded to, when bus access is shielded master, the bus master will not be able to get access , even if no other bus master access the same time. Meanwhile, Slave master signal to be recorded in order to inform future restoration priority arbiter of the master . This can be emitted from the HMASTER arbitrator [3: 0] signal Richard. If all the master have received SPLIT response signal, the arbiter bus access will be transferred to the dummy master (one kind only send master IDLE transmission).
When the response to the SPLIT slave processed transmission requirements, will be issued HSPLIT. [15: 0] signals to the master arbiter HSPLIT samples of each rising edge of the clock [15: 0], when it receives HSPLIT [15 : 0], the original will be masked master of bus priority re-opened, so the master priority will revert to the original state and have the opportunity to regain access to the bus.
1.4 RETRY transmission
When RETRY response signal issued by slave, the master priority arbiter does not change. But when there are higher priority bus master issuing a request signal, the bus will get access to a high-priority master, but if you get the original master RETRY response time is the master bus request of highest priority, the or continue to occupy the bus will be, and can not be released to other needy master.