How can user logic connect to Avalon bus?

Can you recommend me some examples which has been implemented by others? for example, some hyperlink and thank you very much!

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Yes. Avalon is just like any other bus specification. Its similar to axi (although not identical) and can be made to talk to axi with some minor interface conversion.

https://www.altera.com/content/dam/altera-www/global/en_us/pdfs/literature/manual/mnl_avalon_spec.pdf

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