Avalon® Interface Specifications

ID 683091
Date 1/24/2022

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5.4. Avalon® -ST Interface Properties

Table 18.   Avalon® -ST Interface Properties
Property Name Default Value Legal Values Description
associatedClock 1 Clock interface The name of the Avalon® Clock interface to which this Avalon® -ST interface is synchronous.
associatedReset 1 Reset interface The name of the Avalon® Reset interface to which this Avalon® -ST interface is synchronous.
beatsPerCycle 1 1,2,4,8 Specifies the number of beats transferred in a single cycle. This property allows you to transfer 2 separate, but correlated streams using the same start_of_packet, end_of_packet, ready and valid signals.

beatsPerCycle is a rarely used feature of the Avalon® -ST protocol.

dataBitsPerSymbol 8 1 – 512 Defines the number of bits per symbol. For example, byte-oriented interfaces have 8-bit symbols. This value is not restricted to be a power of 2.
emptyWithinPacket false true, false When true, empty is valid for the entire packet.
errorDescriptor 0 List of strings A list of words that describe the error associated with each bit of the error signal. The length of the list must be the same as the number of bits in the error signal. The first word in the list applies to the highest order bit. For example, “crc, overflow" means that bit[1] of error indicates a CRC error. Bit[0] indicates an overflow error.
OrderBits true true, false When true, the first-order symbol is driven to the most significant bits of the data interface. The highest-order symbol is labeled D0 in this specification. When this property is set to false, the first symbol appears on the low bits. D0 appears at data[7:0]. For a 32-bit bus, if true, D0 appears on bits[31:24].
maxChannel 0 0 – 255 Maximum number of channels that a data interface can support.
readyLatency 0 0 – 8

Defines the relationship between the assertion of a ready signal and the assertion of a valid signal. If readyLatency = <n> where n > 0, valid can be asserted only <n> cycles after assertion of ready.

For example, if readyLatency = 1, when the sink asserts ready, the source needs to respond with a valid assertion at least 1 cycle after it sees the ready assertion from the sink.

readyAllowance 1 0 0 – 8

Defines the number of transfers that the sink can capture after ready is deasserted.

When readyAllowance = 0, the sink cannot accept any transfers after ready is deasserted. If readyAllowance = <n> where <n> is greater than 0, the sink can accept up to <n> transfers after ready is deasserted.

Note: If you generate an Avalon® streaming interconnect with Avalon® streaming source/sink BFMs or custom components and these BFMs or custom components have different readyLatency requirements, Platform Designer will insert adapters in the generated interconnect to accommodate the readyLatency difference between the source and sink interfaces. It is expected that your source and sink logic adheres to the properties of the generated interconnect.
  • If readyLatency = 0, readyAllowance can be 0 or greater than 0.
  • If readyLatency > 0, readyAllowance must be equal to or greater than readyLatency.
  • If the source or the sink do not specify a value for readyAllowance then readyAllowance = readyLatency. Designs do not require the addition of readyAllowance unless you want the source or the sink to take advantage of this feature.