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Accelerator Coherency Port

Shakith Fernando
Note: This was originally posted on 25th January 2013 at http://forums.arm.com

Hi all,

I'm trying to use the AcceleratorCoherency Port of the ARM A9MPCORE in the Xilinx Zynq platform (http://www.xilinx.co...vices/index.htm).

1.[size="2"]  [/size]I have a functionaldesign where DMA in the FPGA region is able read and write data through the ACP.But is there direct way to verify that the data is coming from the cacheitself. Only option is to measure cache hits using the PL310 cache controllerevent registers againist a known data set size. But it's a not exact solution,as there may be cache hits in the L1 cache hits instead of L2.

2. As mentioned here (http://forums.arm.co...pcore-acp-port/),I downloaded the Ds5 tools to get access to the reference design, but there is nospecific target design for the ACP. The startup code that enables MMU, L1 cachesand SCU should be enough to make sure the ACP is getting the data from cache?

3.  Cacheable region setting can be set in the MMU table. Butdoes it guarantee exclusive access to a fixed memory region. Maybe if a linux osis running, then it can cause cache thrashing. Is there way to set priority forthe region?

4. Is there support for linux for this. As I understand the ACP istechnically a hardware thing and should be transparent to software. Only thing isto do would be to expose the memory region from kernel space to user space togive it to the DMA engine.

Thanks in advance.
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  • Note: This was originally posted on 14th February 2013 at http://forums.arm.com

    I got the PMU registers working using inline assembly code for the cp15 registers method.

    I have also enabled ACP coherent read and write requests using[font=Verdana, Tahoma, Arial, Helvetica, sans-serif] this[/font][font=Verdana, Tahoma, Arial, Helvetica, sans-serif] [/font]http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0388e/index.html

    I am able to monitor and verify the exact number of cache read hits for ACP read  (externel DMS reads from the l1 cache) using the ARM PMU event monitors. I get 72 data cache hits. That is 64 + 8. 8 (4*2) is I guess is for X_mWriteReg function calls.


    start_perfmon();
    X_mWriteReg(0x60000000,0x0,0x00005000); //Start DMA

    X_mWriteReg(0x60000000,0x18,0xFFFF8000);  //Src Address

    X_mWriteReg(0x60000000,0x20,0x80000000); //Dst Address

    X_mWriteReg(0x60000000,0x28,0x00000040); //Number of bytes - 64 bytes

        stop_perfmon();

    But for the otherway around is tricky to verify. (ACP writes- Externel DMA writes to the cache). As it looks like a write through policy from above link, it should be writing to the L2 cache all the ACP writes. Therefore P310 L2 Event counters for data writes should be around 64 or something similar. Strangely it shows zero or one. Is it really write through?

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  • Note: This was originally posted on 14th February 2013 at http://forums.arm.com

    I got the PMU registers working using inline assembly code for the cp15 registers method.

    I have also enabled ACP coherent read and write requests using[font=Verdana, Tahoma, Arial, Helvetica, sans-serif] this[/font][font=Verdana, Tahoma, Arial, Helvetica, sans-serif] [/font]http://infocenter.arm.com/help/index.jsp?topic=/com.arm.doc.ddi0388e/index.html

    I am able to monitor and verify the exact number of cache read hits for ACP read  (externel DMS reads from the l1 cache) using the ARM PMU event monitors. I get 72 data cache hits. That is 64 + 8. 8 (4*2) is I guess is for X_mWriteReg function calls.


    start_perfmon();
    X_mWriteReg(0x60000000,0x0,0x00005000); //Start DMA

    X_mWriteReg(0x60000000,0x18,0xFFFF8000);  //Src Address

    X_mWriteReg(0x60000000,0x20,0x80000000); //Dst Address

    X_mWriteReg(0x60000000,0x28,0x00000040); //Number of bytes - 64 bytes

        stop_perfmon();

    But for the otherway around is tricky to verify. (ACP writes- Externel DMA writes to the cache). As it looks like a write through policy from above link, it should be writing to the L2 cache all the ACP writes. Therefore P310 L2 Event counters for data writes should be around 64 or something similar. Strangely it shows zero or one. Is it really write through?

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