Honored Contributor
Honored ContributorHi Ron,
--- Quote Start --- I have a new Stratix IV GX based PXI Express (PXI Express = PCIe + additional PXI backplane clock/timing strobes) board design, which uses the Altera PCIe Hard IP and DDR3 SDRAM controller. My initial test configuration uses an Avalon MM interface from the PCIe IP to the DDR3 controller. I am set up for 512 MBytes at BAR_1_0, 64 bit pre-fetchable. --- Quote End --- Is this going to be a product, or something only you use in-house? The reason I ask, is that your BAR0 region is pretty large. Your board would probably stop some systems from booting. For example, I have an HP EliteBook with 16GB of RAM and an ExpressCard to PCIe motherboard setup (from OneStopSystems). If I use the Stratix IV GX Development Kit and the MegaWizard flow example with a 256MB BAR0, the machine will not boot. If I reduce the BAR0 to something more typical of a PCIe device (~1MB ), it boots fine. I don't have a PCI analyzer on-hand, but I suspect that the BIOS probably starts up with the x86 processor in 32-bit mode, and it just runs out of address space to map the devices. I also have systems with PCI boards, up to 18 boards in a single cPCI chassis. If the BAR regions on each board are made too large, then the 32-bit x86 host CPU runs out of address mappings. One key aspect when designing a PCI or PCIe device is to have BAR regions as small as you can. The BAR regions only need to be big enough for the system-slot CPU (the CPU with the PCIe root complex) to access registers on the board. Those registers are typically mailboxes and interrupts for CPU-to-CPU communications, and DMA controller control registers. On-board DMA controllers are typically used to move large volumes of data between the board and the system slot CPU. I've been looking at the Qsys PCIe examples, and the Qsys PCIe bridge fails in this regard. It should have an integrated DMA controller capable of implementing scatter-gather DMA lists, with an Avalon-MM address field, a 64-bit PCIe address field, a direction bit, and data length. I haven't looked at all of the MegaWizard and AlteraWiki examples, but I suspect you really need the same kind of bridge. Cheers, Dave
