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Basics: C programming for ARM - AHB transfers

joewu joewu
Note: This was originally posted on 18th September 2007 at http://forums.arm.com

Hello,
Would someone please help me about the next basic things?
I have programed microcontrollers in the past but now I need to work with ARM processors and need some basic pieces to connect the puzzle.
I wil write a C/C++ code for ARM966 but I don't know what to do in the code to communicate to an AHB peripheral. It should be memory mapped but I don't know at what location and if I need to do the memory initalisation at the start of the code or I can read it from somewhere - I have not been able so far to find a clear document about that.
Also, I expect that is enough for me to write to that location in the memory and to read from it and the compiler 'armcc' will take care of generating AHB transaction data that will go to ARM AHB interface ports. I am right or there are specific C functions for AHB transfers in both directions?
I expect to have a library of the C functions that I can use in the code but also somehow I couldn't find the place where it is explained.
I have been digging over RealView 3.0 (Unix) directories in the search for that and I see several header files (like rt_heap.h, rt_memory.h and so on) but I don't have any single C project example where I can see their usage.
I would really apreciate if someone can give me some examples or point me to a location where I can read about that.
The same questions go for the tightly coupled memory (TCM) - where is it in the memory map and so on.
Any help is appreciated.
Thank you very much,
joewu
Parents
  • 0 Arm Employee Badge
    Note: This was originally posted on 20th September 2007 at http://forums.arm.com

    I understand what you are saying but still don't see when the memory map is configured and who decides at what location AHB peripheral will be mapped and how I can know that now in the early development phases.


    All that the ARM966 TRM states is the mapping to the AHB interface.

    Everything *outside* of the core will be defined by the hardware manufacturer - not by the ARM core, so I can't help you here. What peripherals / RAM / memory controllers sit at what address on the AHB bus depends on how the bus is configured by the ASIC manufacturer.

    If you are working with a silicon chip that has already been manufactured then refer to the actual ASIC TRM for the hardware map, if you are working for a company actually designing the ASIC, then go and talk with your hardware guys =)

    The mapping will be fixed for a particular ASIC - so there is not normally a need to set up any mapping using software at boot time.

    I would expect to have a separate address for AHB HRDATA[31:0] bus - is my assumption correct here or it is also taken care of automatically?


    Automatic - hard defined by the ASIC bus implementation normally =)

    These are all the simple basic questions and I believe after a little example it would all click in place for me.


    I think you are trying to make this more difficult than it really is - my example C code above is *all* that you need to do to talk to a peripheral on the ARM966. There is nothing else to turn into an example.

    You just need to read the ASIC TRM from the hardware mfr. to find out the constant that defines YOUR_PERIPHERAL_BASE_ADDRESS.
Reply
  • 0 Arm Employee Badge
    Note: This was originally posted on 20th September 2007 at http://forums.arm.com

    I understand what you are saying but still don't see when the memory map is configured and who decides at what location AHB peripheral will be mapped and how I can know that now in the early development phases.


    All that the ARM966 TRM states is the mapping to the AHB interface.

    Everything *outside* of the core will be defined by the hardware manufacturer - not by the ARM core, so I can't help you here. What peripherals / RAM / memory controllers sit at what address on the AHB bus depends on how the bus is configured by the ASIC manufacturer.

    If you are working with a silicon chip that has already been manufactured then refer to the actual ASIC TRM for the hardware map, if you are working for a company actually designing the ASIC, then go and talk with your hardware guys =)

    The mapping will be fixed for a particular ASIC - so there is not normally a need to set up any mapping using software at boot time.

    I would expect to have a separate address for AHB HRDATA[31:0] bus - is my assumption correct here or it is also taken care of automatically?


    Automatic - hard defined by the ASIC bus implementation normally =)

    These are all the simple basic questions and I believe after a little example it would all click in place for me.


    I think you are trying to make this more difficult than it really is - my example C code above is *all* that you need to do to talk to a peripheral on the ARM966. There is nothing else to turn into an example.

    You just need to read the ASIC TRM from the hardware mfr. to find out the constant that defines YOUR_PERIPHERAL_BASE_ADDRESS.
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