Hi Detlev, Many thanks for your help. I tried the second option you told me. At my current installation I went to /opt/embedded/linux_2_6 and run "make menuconfig" to configure the kernel. I could not find any option to configure the DEVTMPFS device. I checked many menu items but it was useless.
This installation was performed using the Embedded Planet BSP provided CD. Following your suggestion I downloaded ELDK 4.2 from the ELDK FTP server and successfully installed it. But now I do not know how should I have to configure the kernel for the ELDK 4.2. I checked the online documentation for the ELDK at denx.de web page, but I didn't found anything related to kernel configuration. At installed folder, I have a ppc_4xx folder which contains some folder that appears to belong to a Linux distribution. Now I have two questions: 1) Is it possible to configure this kernel option from the provided BSP (I think i have a 2.6 kernel version)? 2) Is it only ELDK 4.2 a set of tools for target compilation? How can I use it to configure and build a valid kernel image suitable for my target board? I tried to search for this at online documentation unsuccessfully. Cheers Alberto 2010/9/28 Detlev Zundel <[email protected]> > Hi Alberto, > > > I am trying to connect a cable that includes a FTDI device into my > EP440xS > > board. Following the comments found at some forums and web pages, I > > configured the kernel so now I have USB serial converter support (not > > compiled as a module), generic USB serial converter support and FTDI > > support. After that, I downloaded my new kernel image into the board, > > start-up the system, check that the USB subsystem was initializating and > > then plug my cable into the system. After issuing a "dmesg" command, I > found > > out that the device was recognized, but no /dev/ttyUSB0 device was > created. > > This is expected unless you provide means by which such a device file > can be created. > > The first option would be to use something like udev. You need to > explicitely enable udev in ELDK 4.2 by either running 'start_udev' as > superuser manually or by enabling the call to it in /etc/rc/sysinit in > line 323. > > For embedded systems, I would much rather look at option 2, namely > enabling the devtmpfs filesystem in the linux kernel. This is the > config option: > > drivers/base/Kconfig:19 > "Device Drivers" > ---> "Generic Driver Options" > config DEVTMPFS > bool "Maintain a devtmpfs filesystem to mount at /dev" > depends on HOTPLUG > help > This creates a tmpfs/ramfs filesystem instance early at bootup. > In this filesystem, the kernel driver core maintains device > nodes with their default names and permissions for all > registered devices with an assigned major/minor number. > Userspace can modify the filesystem content as needed, add > symlinks, and apply needed permissions. > It provides a fully functional /dev directory, where usually > udev runs on top, managing permissions and adding meaningful > symlinks. > In very limited environments, it may provide a sufficient > functional /dev without any further help. It also allows simple > rescue systems, and reliably handles dynamic major/minor numbers. > > Notice: if CONFIG_TMPFS isn't enabled, the simpler ramfs > file system will be used instead. > > Also be sure to enable this option: > > drivers/base/Kconfig:39 > "Device Drivers" > ---> "Generic Driver Options" > config DEVTMPFS_MOUNT > bool "Automount devtmpfs at /dev, after the kernel mounted the > rootfs" > depends on DEVTMPFS > help > This will instruct the kernel to automatically mount the > devtmpfs filesystem at /dev, directly after the kernel has > mounted the root filesystem. The behavior can be overridden > with the commandline parameter: devtmpfs.mount=0|1. > This option does not affect initramfs based booting, here > the devtmpfs filesystem always needs to be mounted manually > after the roots is mounted. > With this option enabled, it allows to bring up a system in > rescue mode with init=/bin/sh, even when the /dev directory > on the rootfs is completely empty. > > Then the device should show up after plugging it in. > > Cheers > Detlev > > -- > But solicitors and stockbrokers and bookmakers often lead comfortable and > happy lives, and it is very difficult to see how the world is richer for > their existence. -- G. H. Hardy > -- > DENX Software Engineering GmbH, MD: Wolfgang Denk & Detlev Zundel > HRB 165235 Munich, Office: Kirchenstr.5, D-82194 Groebenzell, Germany > Phone: (+49)-8142-66989-40 Fax: (+49)-8142-66989-80 Email: [email protected] >
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