DMEM & MEM_EXT

[GTrannoy]

Hi,

I would have used the internal DMEM for working RAM simultaneously with an external memory accessed with AXI4-lite and I don't know if it is possible.

In the documentation, I see that DMEM could not be implemented to use external accesses...

But I would have do it in the way the Linker is classical and identify DMEM as RAM at address 0x80000000 as in the documentation.
And I would set-up a memory at addres 0x90000000 for example. Something different from this one of the RAM.
I guess, this is no need to specify it into the linker as it would only be accessed through the program.

I saw in the "neorv32_wishbone.vhd" that address outside DMEM_SIZE is not considered as internal access. i.e. int_dmem_acc is at '0' and so xbus_access could be set at '1' and authorized the transaction.

Is it possible ?
Can I have DMEM and MEM_EXT simultaneously at differents addresses ?

[stnolting]

Can I have DMEM and MEM_EXT simultaneously at differents addresses ?

To make it short: Yes, of course! 😉

All address accesses that do not target the internal DMEM (if implemented) and not the internal IMEM (if implemented) and not the internal boot ROM and not the internal peripherals are forwarded to the external memory interface.

I saw in the "neorv32_wishbone.vhd" that address outside DMEM_SIZE is not considered as internal access. i.e. int_dmem_acc is at '0' and so xbus_access could be set at '1' and authorized the transaction.

Correct. So if you access address 0x90000000 and the internal DMEM is smaller than 256 MB (= difference between 0x80000000 and 0x90000000) then this access will be forwarded to the Wishbone / AXI interface.

I guess, this is no need to specify it into the linker as it would only be accessed through the program.

Right. There is no need to modify the linker script for your setup.

[GTrannoy]

Thank you very much for your answer !
It clarifies what I thought.