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jackhab's avatar
jackhab
Icon for Occasional Contributor rankOccasional Contributor
3 years ago

Reading data from FPGA on HPS with Linux - what's the best way to do it?

I have a Cyclone V with Linux application on ARM.

The application accesses FPGA directly by mapping HW light- and heavy-weight bridges into virtual memory space (without kernel driver).

Currently, I have a working application which does all access via alt_read_word() and alt_write_word().

I recall from NIOS documentation that this is the proper way to access HW memory to avoid caching issues but I couldn't find anything about it with regards to ARM. So I'd like to ask the following:

  1. Should FPGA memory be accessed by HPS only via SoCAL Memory Read/Write Utilities or it can be used as normal HPS RAM including calling memcopy() to move data between FPGA and HPS?
  2. Is there a document for SW developers which describes how HPS should access FPGA memory space?

Thanks.

4 Replies

  • jackhab's avatar
    jackhab
    Icon for Occasional Contributor rankOccasional Contributor
    2 years ago

    Hi Tiwari

    I, indeed, use mmap() to gain access to FPGA memory space. But my question was about what happens during actual read and write.

    Should I read the memory word-by-word using alt_read_word() function or reading big memory chunks using standard memcpy() also OK?

    I am asking it because I'm not sure how ARM's data caching will behave during mempcpy() and I'm afraid caching can cause data corruption.

  • Jeet14's avatar
    Jeet14
    Icon for Frequent Contributor rankFrequent Contributor
    2 years ago

    Hi,


    Cross-compiler vendors generally include a precompiled set of standard class libraries, including a basic implementation of memcpy() . Unfortunately, since this same code must run on hardware with a variety of processors and memory architectures, it can't be optimized for any specific architecture.


    A variety of hardware and software factors might affect your decision about a memcpy() algorithm. These include the speed of your processor, the width of your memory bus, the availability and features of a data cache, and the size and alignment of the memory transfers your application will make.


    An intimate knowledge of your target hardware and memory-transfer needs can help you write a much more efficient implementation of custom memcpy() functions.

    You can also refer below link on memcpy and custom memcpy functions-

    https://www.intel.com/content/www/us/en/developer/articles/technical/performance-optimization-of-memcpy-in-dpdk.html


    I suggest you to use the data reading using driver APIs i.e. alt_read_word();


    Regards

    Jeetesh



  • Jeet14's avatar
    Jeet14
    Icon for Frequent Contributor rankFrequent Contributor
    2 years ago

    Hi,

    If you have any other question on the matter, please let me know.

    Regards

    Jeetesh