Avalon® Interface Specifications

ID 683091
Date 1/24/2022
Public

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6.3.1. Per-Symbol User Signal

As the name suggests, the data defines a per-symbol user signal (symbol_user) per symbol. Each symbol in the data can have a user signal. For example, if the number of symbols in the data is 8, and symbol_user width is 2 bits, the total width of the symbol_user signal is 16 bits.

Symbol_user is valid only when data is valid. Source can change this signal every cycle when data is valid. Sink can disregard the value of symbol_user bits for empty symbols.

If a source which has this signal is connected to a sink which does not have this signal on its interface, the signal from source remains dangling in the generated interconnect.

If a source which does not have this signal is connected to a sink which has this signal on its interface, the sink’s input user signal ties to 0.

If both source and sink have equal number of symbols in the data, then the user signals for both must have equal widths. Otherwise, they cannot be connected.

If a wide source is connected to a narrow sink, and both have per-symbol user signals, then both must have equal bits of user signal associated with each symbol. For example, if a 16-symbol source has 2 bits of user signal associated with each symbol (for a total of 32 bits of user signal), then a 4-symbol sink must have an 8-bit wide user signal (2 bits associated with each symbol). A data format adapter can convert the 16-symbol source data to 4-symbol sink data, and 32-bit user signal to 8-bit user signal. The data format adapter maintains the association of symbols with corresponding user signal bits.

Similarly, if a narrow source is connected to a wide sink, and both have per-symbol user signals, then both must have equal bits of user signal associated with each symbol. For example, if a 4-symbol source has 2 bits of user signal associated with each symbol (for a total of 8 bits of user signal), then a 16-symbol sink must have a 32-bit wide user signal (2 bits associated with each symbol). A data format adapter can convert the 4-symbol source data to 16-symbol sink data, and 8-bit user signal to 32-bit user signal. The data format adapter maintains the association of symbols with corresponding user signal bits. If the packet is smaller than the ratio of data widths, the data format adapter sets the value of empty accordingly. Sink should disregard the value of user bits associated with empty symbols.