xilinx_zynq_zc702 vs. xilinx_zynq_zc706 memory map

[Sebastian Huber]

On 24/10/2019 03:41, Jonathan Brandmeyer wrote:
> On Wed, Oct 23, 2019 at 6:04 AM Thomas Doerfler
> <thomas.doerfler at embedded-brains.de> wrote:
>>
>> Hi,
>>
>> most likely the RAM areas have been mapped to the lowest-possible
>> non-NULL address, and they can be mapped to an address boundary matching
>> the RAM size. zc702 has a 1MByte ram, mapped to the 1MByte boundary,
>> zc706 has a 4MByte RAM mapped to the 4MByte boundary.
> 
> I don't know what the actual rationale is, but this definitely isn't
> it.  The DDR physical address mapping is fixed.  The lower 256k can be
> mapped to DRAM or on-chip SRAM depending on system settings.  The
> range from 256k - 1M is either inaccessible or mapped to DRAM.  The
> range from 1M - 4M is always mapped to DRAM.  Its an
> application-profile processor, which is why the typical sizes are 512M
> or 1024M (SoC maximum) for DRAM.
> 
> See also Xilinx UG585, section 4.1.
> 
> The chip's reset defaults are for 192 kB of OCM to be mapped low, and
> 64 kB to be mapped high with address filtering disabled.


Yes, the DDR is surly greater than 4MiB. The unused 1MiB starting a 0 is 
there to catch NULL pointer access (read, write, and execute). Why the 
xilinx_zynq_zc706 has an unused 4MiB area is not clear to me.

-- 
Sebastian Huber, embedded brains GmbH

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