Code Confidencebuild

Example Host-side Device Driver


Example Host-side Device Driver -- Provide host-side support for the eCos USB-ethernet package


The USB-ethernet package is supplied with a single host-side device driver. This driver has been developed against the Linux kernel 2.2.16-22, as shipped with Red Hat 7. The driver is provided as is and should not be considered production quality: for example it only checks for a bogus vendor id 0x4242 rather than an official vendor id supplied by the USB Implementers Forum. Also, if the peripheral involves multiple configurations or multiple interfaces, it will fail to detect this. However, the driver can be used for simple testing and as the basis of a full device driver. Details of the protocol used between host and peripheral can be found in the Communication Protocol section.

The host-side device driver can be found in the host subdirectory of the USB-ethernet package, specifically the file ecos_usbeth.c, and comes with a Makefile. Both files may need to be modified for specific applications. For example, the vendor id table ecos_usbeth_implementations may need to be updated for the specific USB peripheral being built. The Makefile assumes that the Linux kernel sources reside in /usr/src/linux, and that the kernel has already been configured and built. Assuming this is the case, the device driver can be built simply by invoking make with no additional arguments. This will result in a dynamically loadable kernel module, ecos_usbeth.o, in the current directory.

Note: As normal for Linux kernel builds, the generated files such as ecos_usbeth.o live in the same directory as the source tree. This is very different from eCos where the source tree (or component repository) is kept separate from any builds. There may be problems if the component repository is kept read-only or if it is put under source code control. Any such problems can be avoided by making a copy of the host subdirectory and building that copy.

Loading the kernel module into the current system requires root privileges. If the generic USB support is also a loadable module and has not been loaded already, this must happen first:

# insmod usb-uhci
Using /lib/modules/2.2.16-22/usb/usb-uhci.o

Depending on the host hardware, the uhci or usb-ohci modules may be more appropriate. Loading the generic USB module will typically result in a number of messages to the logfile /var/log/messages, giving details of the specific host-side hardware that has been detected plus any hubs. The next step is to load the USB-ethernet module:

# insmod ecos_usbeth.o

This should result in a number of additional diagnostics in the logfile:

Apr 1 18:01:08 grumpy kernel: eCos USB-ethernet device driver
Apr 1 18:01:08 grumpy kernel: usb.c: registered new driver ecos_usbeth

If a suitable USB peripheral is now connected the host will detect this, assign an address in the local USB network, obtain enumeration data, and find a suitable device driver. Assuming the peripheral and device driver agree on the supported vendor ids, the ecos_usbeth.o module will be selected and this will be reported in the system log:

Apr 1 18:04:12 grumpy kernel: usb.c: USB new device connect, assigned device number 3
Apr 1 18:04:12 grumpy kernel: eCos-based USB ethernet peripheral active at eth1

What can happen next depends very much on the software that is running on top of the USB-ethernet package inside the peripheral. For example, if there is a TCP/IP stack then it should be possible to bring up a network connection between host and peripheral using ifconfig.