PCI bridge or custom FPGA to build a PCI Master + SDRAM ?

Whats the major difference between using a PCI bridge or a custom FPGA to build a PCI Master + SDRAM controller?
What is the better solution?

Re: PCI bridge or custom FPGA to build a PCI Master + SDRAM

Not sure if I understand what you meen.

If you wish to have a board that act as PCI slave AND master, and on this board, have SDRAM, with controller, you bettwe use FPGA and integrate everything in FPGA.

If you wish to have SDRAM off-board, and access-it with your board, acting as PCI master, this can still be done with FPGA.

I've seen some custom PCI bridge chips, but there practically are all PCI slaves.

Re: PCI bridge or custom FPGA to build a PCI Master + SDRAM

I have abs. no experience in FPGA.
Thats why I think, that PCI bridge is better, but how to attach a SDRAM controller to that bridge?

If PCI bridges with PCI Master are rare, then maybe its better to start with PCI Express bridge which is for sure is a Master ?

Re: PCI bridge or custom FPGA to build a PCI Master + SDRAM

PCI and PCI express are simply BUS architecture. Both of them can support add-in cards, which can either be master, target, or both.

In a PCI subsystem, any add-in cards can perform requests to the PCI bus. So, you can have the main processor who access a card, or memory, and in turn, your own card can also access the system main memory, transparently, without disturbing the main processor. The ability for your board to access other interfaces over the PCI bus is 'master'. If your board only get access from the main CPU or another master on the PCI bus, then you probably only need a 'target' PCI interface.

Example of target and master boards are:

target:
- many video cards which have on-board memory (though, those are usually AGP, AGP is similar to PCI. Some cards are PCI).
- Most Ethernet controlers
- Many sound cards

target AND master:
- Video cards which rely on the main system memory (which use what that call 'shared memory').
- All the cards that access the main system memory on their own.

So, if your card doesn't need to generate their own transactions on the system PCI bus, they you probably don't need a master PCI interface.

Note that both master and targets can still generate interrupt requests.

If you look at opencores.org, there is a PCI core (opensource). I havn't tried it yet though. The PCI act as a bridge between PCI and an opensource bus standard called Wishbone. Wishbone is pretty straightforward. That core is both a target and master, though you can use what you want.