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Is it possible to increase the MSP430 USB CDC API packet size?

louis liu
Intellectual 445 points


The above two links are the latest and the early MSP430 USB CDC API programmer’s Guide. Both show the packet size is 64 bytes max.  In our device tested, this is true and limit some of our functions.  Such as SCADA protocol BSAP communication with device, firmware field updates, and user defined LCD contents setup.  If TI can help to increase this size up to 255 bytes, it will help us to make BSAP communication on USB works, make field update firmware run faster.  

to find the document reference to packet size as following: 

in link 1, July 2012 document before section 9.5 it states the packets size.

in link 2, July 2009 document before section 5.3; it states the packets size.

  • 0
    TI__Guru**** 219937 points
    Hi Louis,

    There are several locations inside the latest release of the Programmer's Guide (July 2012) mentioning that the packet size is limited to 64 bytes, therefore it seems like the application you are trying to achieve is not possible. However I am currently looping in a MSP430 USB expert to further comment on the matter.

    Regards,
    Ryan
  • 0
    Guru 319070 points

    The USB specification limits full-speed bulk packets to 64 bytes; more is not possible.

    However, the USB packet size is not the same your own buffer size; the CDC functions can work with larger application buffers (which are automatically split into USB packets, and pipelined).

  • 0
    Guru 34773 points

    MSP430 USB module has endpoints with 64 bytes max length (except endpoint 0, that has 8 bytes).  However, it can send CDC / Bulk continuously (at once) data stream up to 1 MByte / s. Don't know about SCADA, but if you are flashing faster than 1 MByte / s, than CDC on MSP430 can be limiting factor. TI will not not increase endpoint size of MSP430 USB module for sure (don't know about MSP432).

  • 0 in reply to zrno soli
    TI__Expert 6760 points
    Both Clemens and Zrno are correct. Packet size is limited to 64 bytes. But your buffer size can be greater than 64 bytes. There are examples of how this can be done included in the MSP430DevelopersPackage for CDC.

    Regards,
    Arthi Bhat

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