Avalon® Interface Specifications

ID 683091
Date 9/26/2022
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6.2. Avalon® Streaming Credit Interface Signal Roles

Each signal in an Avalon® Streaming Credit source or sink interface corresponds to one Avalon® Streaming Credit signal role. An Avalon® Streaming Credit interface may contain only one instance of each signal role. All Avalon® Streaming Credit signal roles apply to both sources and sinks and have the same meaning for both.

Table 20.   Avalon® Streaming Credit Interface Signals
Signal Name Direction Width Optional / Required Description

update

Sink to source

1

Required

Sink sends update and source updates the available credit counter. Sink sends update to source when a transaction is popped from its buffer.

Credit counter in source is increased by the value on the credit bus from sink to source.

credit

Sink to source

1-9

Required

Indicates additional credit available at sink when update is asserted.

This bus carries a value as specified by the sink. Width of the credit bus is ceilog2(MAX_CREDIT + 1). Sink sends available credit value on this bus which indicates the number of transactions it can accept. Source captures credit value only if update signal is asserted.

return_credit

Source to sink

1

Required

Asserted by source to return 1 credit back to sink.

Note: For more details, refer to Section 6.2.3 Returning the Credits.

data

Source to sink

1-8192

Required

Data is divided into symbols as per existing Avalon® Streaming definition.

valid

Source to sink

1

Required

Asserted by the source to qualify all other source to sink signals. Source can assert valid only when the credit available to it is greater than 0.

error

Source to sink

1-256

Optional

A bit mask used to mark errors affecting the data being transferred in the current cycle. A single bit in error is used for each of the errors recognized by the component, as defined by the errorDescriptor property.

channel

Source to sink

1-128

Optional

The channel number for data being transferred on the current cycle.

If an interface supports the channel signal, it must also define the maxChannel parameter.

Packet Transfer Signals

startofpacket

Source to sink

1

Optional

Asserted by the source to mark the start of a packet.

endofpacket

Source to sink

1

Optional

Asserted by the source to mark the end of a packet.

empty

Source to sink

ceil(log2(NUM_SYMBOLS))

Optional

Indicates the number of symbols that are empty, that is, do not represent valid data. The empty signal is not used on interfaces where there is one symbol per beat.

User Signals

<Per-Packet User Signals>

Source to sink

1-8192

Optional

Any number of per-packet user signals can be present on source and sink interfaces. Source sets value of this signal when startofpacket is asserted. Source should not change the value of this signal until start of new packet. More details are in the User Signal section.

<Per-Symbol User Signals>

Source to sink

1-8192

Optional

Any number of per-symbol user signals can be present on source and sink. More details are in the User Signal section.