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Which peripherals are using top 64 MB of HPS DDR?


I am using cyclone V with 1GB DDR. When I try to run a baremetal application from OCRAM to read and write to every possible address of DDR, it always fails on top 64 MB. I tried searching in the HPS manual for any references about this memory being used by peripherals and found this statement under section "Functional Description of HPS-to-FPGA bridge".


"The effective size of the address space is 0x3FFF0000, or 1 gigabyte (GB) minus

the 64 megabytes (MB) occupied by peripherals, lightweight HPS-to-FPGA bridge, on-chip RAM, and

boot ROM in the HPS."


But as I understood, this statement refers to FPGA DDR and not HPS one. Is my understanding correct? Can you give any other reference to what might be the cause of failure of memory test for top 64 MB addresses?

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3 Replies
Honored Contributor III

This is the address map from the processor's point of view, so yes, the top 64 MB is used by the items listed.



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Thanks for your reply but I don't think that is correct. I think the statement in the manual is referring to FPGA DDR address space, starting at 0xC0000000.

FPGA slave region is anyway of size 960 MB (1024 MB - 64MB), which confirms that the top 64 MB of FPGA DDR is being used by the things mentioned above.

Also, there is a typo in that statement, 1024MB - 64 MB = 960 MB, (which in hex is 0x3C000000 and not 0x3FFF0000).


I also made a mistake while posting, my application fails for top 64 KB (starting from 0x3FFF0000). So now the question is, are there any peripherals using top 64 KB of HPS DDR?



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The top 64MB of address space is the HPS peripherals region.


The HPS peripherals region is always allocated to the HPS dedicated peripherals for the Cortex-A9 MPU subsystem.


Regarding the 64 KB on the boot region:

The boot region is 1 MB in size, based at address 0. After power-on, the boot region is occupied by the boot ROM, allowing the Cortex-A9 MPCore to boot.

Though the boot region size is 1 MB, accessing beyond 64 KB are illegal because the boot ROM is only 64 KB.


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