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Embedded Linux and PCI (over AT91?)

Hello,

I'm currently making the initial design decisions (and hence the most important ones) about a project, which will involve a processor running Linux. The project's initial definition is to take data from an MPEG video chipset and store the stream in a long file on a Disk-on- Key.

So the concept is simple: Write a driver for whatever video hardware we're going to choose (still not defined), and make use of the Linux environment to handle all the USB and filesystem magic. Left on the todo-list is to write a simple application to copy the data. Neat and simple. Or so I thought.

The first headache was to choose the processor. I was told that ARM9 is the preferred architecture (for historic reasons, so this issue is open) and I'm pretty much in favor of Atmel AT91RM9200, mainly because it appears to have some community mileage (see

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).

And now to the point: I'd like the processor to talk with some of its peripherals over a PCI bus. For example, the on-chip USB 2.0 is only full-speed, which may be too slow for a video stream, so I'd like the option to connect a high-speed USB chipset over the PCI bus (I suppose such are available).

Another thing is that my company is pretty responsive to customer's bizarre demands, so we need the flexibility to quickly acquire some Linux-supported PCI chipset, which implements some unexpected interface (firewire? IDE? SCSI?). Then make some small changes to the board (basically hook the device on the on-board bus), and have the product up quickly and painlessly.

In a survey I made, I found out that this is not something people do: Very few processors I found have 16-bit PCMCIA, which is the closest I got to PCI. I think I saw some PCI connectivity on Intel's IOP (XScale), but there were too many Gigas mentioned in the datasheet to make it look like a fitting solution for a small module.

So this leads me to basically two questions:

  1. Is trying to connect a PCI bus to a AT91 inherently stupid? If so, why? (I mean, if it was such a good idea, I would expect it implemented on development boards)
  2. What is the simplest way to get any simple processor to have a PCI bus, in such a way that Linux will recognize it naturally? (Assuming the answer to question #1 is "no")

And, by the way, the first thing I suggested was a simple i386-based single board computer. Judging by the allergic response I got, I found no reason to investigate this direction further.

Thanks in advance (and a happy new hangover) Bill

Reply to
bill.valores
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Have you considered getting an ARM9 with integrated high speed USB ?

For instance:

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Reply to
Arlet Ottens

I thought 'full speed' applied to USB 1 / 1.1 and that 2.0 devices had to be able to go faster than that?

Anyway, to talk to a usb disk you also need a device which implements the USB host and not simply a USB device interface.

Assuming you are writing compressed video data, USB full speed probably is fast enough for most purposes. If I recall correctly USB full speed is 12 mbit/second minus overhead, wheras the official limit for DVD's is a little under 10 mbit/second. But if you can't do good compression before writing it you might have to go faster.

Most current usb flash disks will write on the order of 5 MByte/second when used with USB2.0, but those a little older may be substantially slower.

Looking at your requirements, an embedded x86 platform probably is the best choice. You can buy an entire micro laptop with usb2.0, 2g internal storage, and display (Asus EeePC 2g) for the $300 we're paying for an embedded blackfin module

Reply to
cs_posting

No. USB 2.0 is just a standard. It supports low, full and high speed devices. The USB 1.1 standard, on the other hand only supports low and full speed devices.

To comply with the USB 2.0 standard, a device only needs a couple more descriptors.

The overhead on USB is quite big. I don't think you can get 10 Mbps effective throughput on a full speed device, even if you completely saturate the bus.

Reply to
Arlet Ottens

Hide quoted text -

Not this specific chip (which looks like it has a USB peripheral port and not a host), but I did have a peek on Freescale's i.MX27/i.MX31 and TI's DaVinci (TMS320DM6446). They also have some added value regarding video compression, and their price is high but OK. But while these chips have official Linux support, they don't appear to have a Linux community backing them up, which means using Linux without Linux' main advantage.

Anyhow, this doesn't address the orig> Looking at your requirements, an embedded x86 platform probably is the

The solution should still be a tiny card in another piece of electronics, and pretty honestly I don't have much of a say in this matter. All mini-PC solutions are out of the question. I may be able to push a x86-based solution, in case it has a embedded-like feel, but I haven't found any developmend board which doesn't scream "Computer", both in spec and design.

Thanks so far, Bill.

Reply to
bill.valores

[...]

Not exactly stupid, but hard. None of the AT91 members has native PCI, and so the AT91 Linux port doesn't. You'll have to add a LocalBus-PCI Host Bridge (fixed-function chip or FPGA), and you'll have to add PCI support to your Linux kernel. Good luck. I can't guantantee that you are even able to implement the full PCI 2.2 standard, eg. when it comes to items like busmaster DMA from/to DRAM.

I'd strongly advise you to stay away from this. If you feel you need PCI, choose a controller with native PCI support. Even with ARM9 there are several ones. And MIPS, PPC, Coldfire exist.

And if you need high-speed USB2.0 or Gigabit Ethernet, don't forget performance. I'm unsure about high-speed USB, but at least for Ethernet the controller won't gain much from a gigabit phy.

Mit freundlichen Grüßen

Frank-Christian Krügel

Reply to
Frank-Christian Kruegel

Hide quoted text -

That is a rather subjective criterion. It would help if you provided some more objective criteria which could be used to determine what is acceptable and what not.

Reply to
Dombo

skrev i meddelandet news: snipped-for-privacy@e23g2000prf.googlegroups.com...

Check out

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which has implemented a PCI bridge to an AT91RM9200 using an FPGA. They have a Linux port for it.

--
Best Regards,
Ulf Samuelsson
This is intended to be my personal opinion which may,
or may not be shared by my employer Atmel Nordic AB
Reply to
Ulf Samuelsson

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