Spring 2010 Prof. Hyesoon Kim• Single clock edge protocolARM Core/CPU On-chip RAM DMA controllerbridgeTest i/f ctrlExternal bus interfaceUARTtimerParallel i/fAHB or ASBAPB• AHB (Advanced High-performance Bus) – New standard – Connect high-performance system – Burst mode data transfer and split transactions – Pipelined • ASB (Advanced System Bus)– Old standard – Connect high-performance system – Pipelined – Multiple systems • APB (Advanced Peripheral Bus)– A simpler interface for low-performance peripherals – Low power– Latched address, simple interfaceMaster 1Master 2Master 3Slave 1Slave 2Slave 3ArbiterDecoderAddrdataRead dataBus grant• A bus transaction is initiated by a bus master which requests access from a central arbiter.• The arbiter decides priorities when there are conflicting requests.• The design of the arbiter is a system specific issue.• The ASB only specifies the protocol:– The master issues a request to the arbiter– When the bus is available, the arbiter issues a grant to the master.wuzwuz.nuigalway.ie/.../SOC_Lecture_02_UCG%20November%2012%202002.ppt• A memory access consists of several cycles (including arbitration)• Since the bus is not used in all cycles, pipelining can be used to increase performance http://www.imit.kth.se/courses/2B1447/Lectures/2B1447_L4_Buses.pdf• A transaction is splitted into a two transactions – Request-transaction – Reply-transaction• Both transactions have to compete for the bus by arbitrationVariable request sizes http://www.imit.kth.se/courses/2B1447/Lectures/2B1447_L4_Buses.pdf• Overheads can be reduced if the requests are sent as a burst • Overheads– Arbitration, Addressing, Acknowledgement• Better efficiency, but be careful with long requests http://www.imit.kth.se/courses/2B1447/Lectures/2B1447_L4_Buses.pdf• Bus bridges are used to separate high-performance devices from low-performance devices• All communication from high-performance bus with the low performance device goes via the bridgehttp://www.imit.kth.se/courses/2B1447/Lectures/2B1447_L4_Buses.pdf• Mali-55: smallest graphics processors • Mali-200 • Mali-400 MP
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