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thanks Dave for ur help, with ur explanations i did it :-). pci express works now in qsys,
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Great!
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heading forward to dma transfers now, hope u can help me with that when i´ve got problems ;-)
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Depending on how you implement the DMA controller you will face a few issues.
Lets say you ask for a 4kB page in the host memory. That memory can be mapped from its virtual address to the physical address. Lets say its address is the 64-bit value 1234_5678_0000_0000h. Now how do you DMA from your Qsys system into that page?
The Qsys PCIe example implements a DMA controller within the Qsys system, and the Qsys system has only 32-bit addresses. Since the DMA controller can only deal with 32-bit Avalon addresses, how then can you access the 64-bit address of the host?
The CRA registers should have a register that allows you to program the most-significant address bits of the TXS slave address. For example, if you setup a single TXS 1MB window, then the 10-LSBs of the address would come from the Avalon TXS access address, while the 64-10 = 54 MSBs should come from a register in the CRA slave.
I haven't used this feature during my testing, but I'm pretty sure that should be how it works.
Cheers,
Dave
Honored Contributor
