[ECOS] Help getting started: PCI/USB

Robin Randhawa robin.randhawa@gmail.com
Tue Apr 11 06:19:00 GMT 2006

On Friday 07 April 2006 02:48, stevemors@gmail.com wrote:

> I have been tasked with a project that involves a PCI-to-USB slave
> device on a PC platform. This is supposed to allow the PC to act as a
> USB slave.

Chipsets that provide a USB Host controller Interface AND a slave device 
interface are becoming increasingly common. Not surprising to see a slave 
only interface for PCs. Would aid slave side USB development I guess.

> 1. Would the driver for this device be a USB driver wrapped in a PCI
> driver? Would I look at existing eCos PCI and USB drivers and create
> some sort of hybrid of these?

As Andrew pointed out, there aren't any drivers for PCI per se. PCI is a 
busing scheme that allows access to peripheral memory with a view to 
dynamically mapping the devices in the CPU's address space and also allowing 
access to the device's configuration space.

In order to use PCI as an access mechanism, a PCI Host controller needs to be 
setup and that is usually done first by the BIOS.

> 2. The PC bios configures the PCI bus and devices. This means CPU-PCI
> address translation is unknown to eCos, correct? How can I fill in
> this information when this configuration has been skipped? (Doesn't
> redboot have to do this?)

The address mappings done for each PCI-accessible device are done via device 
specific Base Address Registers. These are filled in by the BIOS as a 
temporary mapping to allow stuff like ethernet controllers etc to work at 
boot-time. The BARs are re-written by the OS as deemed necessary. I would 
think that eCos would do the same to suit the address map of the platform in 

The key here is to understand that a USB Slave controller is a USB device that 
is accessible to the CPU via a PCI bus.


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