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AvalonMM

The AvalonMM bus fit very well in FPGA. It is very flexible :

• Able to achieve same simplicity as APB

• Can be a better fit than AHB in many applications that need bandwidth because AvalonMM has a mode that decouple read response from commands (reduces read latency impact).

• Has less performance than AXI but uses less area (Read and write commands use the same handshake channel. The master don’t need to store address of pending request to avoid Read/Write hazard)

Characteristics

• ???? REVIEWME

Configuration and instantiation

The AvalonMM Bundle has a construction argument AvalonMMConfig. Because of the flexible nature of the Avalon bus, the AvalonMMConfig as many configuration elements. For more information the Avalon spec could be find here.

case class AvalonMMConfig( addressWidth : Int,
                           dataWidth : Int,
                           burstCountWidth : Int,
                           useByteEnable : Boolean,
                           useDebugAccess : Boolean,
                           useRead : Boolean,
                           useWrite : Boolean,
                           useResponse : Boolean,
                           useLock : Boolean,
                           useWaitRequestn : Boolean,
                           useReadDataValid : Boolean,
                           useBurstCount : Boolean,
                           //useEndOfPacket : Boolean,

                           addressUnits : AddressUnits = symbols,
                           burstCountUnits : AddressUnits = words,
                           burstOnBurstBoundariesOnly : Boolean = false,
                           constantBurstBehavior : Boolean = false,
                           holdTime : Int = 0,
                           linewrapBursts : Boolean = false,
                           maximumPendingReadTransactions : Int = 1,
                           maximumPendingWriteTransactions : Int = 0, // unlimited
                           readLatency : Int = 0,
                           readWaitTime : Int = 0,
                           setupTime : Int = 0,
                           writeWaitTime : Int = 0
                           )

This configuration class has also some functions :

Name	Return	Description
getReadOnlyConfig	AvalonMMConfig	Return a similar configuration but with all write feature disabled
getWriteOnlyConfig	AvalonMMConfig	Return a similar configuration but with all read feature disabled

This configuration companion object has also some functions to provide some AvalonMMConfig templates :

Name	Return	Description
fixed(addressWidth,dataWidth,readLatency)	AvalonMMConfig	Return a simple configuration with fixed read timings
pipelined(addressWidth,dataWidth)	AvalonMMConfig	Return a configuration with variable latency read (readDataValid)
bursted(addressWidth,dataWidth,burstCountWidth)	AvalonMMConfig	Return a configuration with variable latency read and burst capabilities

// Create a write only AvalonMM configuration with burst capabilities and byte enable
val myAvalonConfig =  AvalonMMConfig.bursted(
                        addressWidth = addressWidth,
                        dataWidth = memDataWidth,
                        burstCountWidth = log2Up(burstSize + 1)
                      ).copy(
                        useByteEnable = true,
                        constantBurstBehavior = true,
                        burstOnBurstBoundariesOnly = true
                      ).getWriteOnlyConfig

// Create an instance of the AvalonMM bus by using this configuration
val bus = AvalonMM(myAvalonConfig)