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USB CDC-ACM (USB serial) device help | Cypress Semiconductor

USB CDC-ACM (USB serial) device help

Summary: 1 Reply, Latest post by RSKV on 04 Feb 2014 04:21 PM PST
Verified Answers: 0
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user_2208888's picture
38 posts

Hello, I need to have a device that implements CDC-ACM protocol on the USB side and communicate with the onboard UARD on the other side, something very similat with the cyfxusbuart example that comes with the SDK but with a twist:

I need to modify in the FX 3 firmware the data that comes from the USB and then send it to the UART and viceversa, ie. receive data from the UART in memory modify it and send it to the USB, practially like a smart serial cable that does some protocol translation.

Unfortunately the cyfxusbuart example connects the producer and consumer sockets directly and I actually don't know what will be the best way to be interrupted ( event generation ) when characters are coming both from the USB and from the UART so I can intercept them and do the translation.

Also, any advice about what will be the best setting for the buffer size in this situation will be really appreciated.

Many thanks,



rskv's picture
Cypress Employee
1134 posts

 Hi MC,

You need to have two manual DMA channels created for doing data transfers in both directions.

You can play with the data if you are using a manual DMA channel. You can have a callback function where you get the producer events and modify the data and then commit that data to the other side.

If you are looking for the minimum DMA buffer that you can create then that is 16bytes.


Sai Krishna.

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