Linux for PowerPC Embedded Systems HOWTO: Device Drivers

11. Device Drivers

The kernel already includes device drivers for the on-chip serial and ethernet ports.

11.1 Examples

For helpful MPC8xx-specific device driver examples, see: http://lists.linuxppc.org/listarcs/linuxppc-embedded/200001/msg00221.html

ftp://ftp.denx.de/pub/LinuxPPC/usr/src/drivers.tar.gz

11.2 Flash memory

Flash Device Driver

ftp://ftp.denx.de/pub/LinuxPPC/usr/src/CDK.tar.gz

A flash driver will give you access to /dev/flash devices, which are useful during development, for field upgrades and are ideal for storing fixed size persistent configuration data like your board's Ethernet MAC address. Includes drivers supporting a number of vendor's devices.

The flash driver does auto-erase when the length of data written per write() is exactly the corresponding erase block size. So usually you just need to do:

open (/dev/flash???)
lseek(specific erase region)
write(data, region size)

QSLinux Flash Driver

http://qslinux.org/ ftp://qslinux.org/

QSLinux contains a fully functioning FLASH driver, and an interface to the Ext2FS filesystem, with compression.

Memory Technology Device Subsystem

http://www.linux-mtd.infradead.org/

The MTD subsystem offers a more general solution which allows you to treat the flash as a regular block device on which you can mount a filesystem. It's ideal for large amounts of variable sized data or applications requiring a traditional writable filesystem, provided by the Journaling Flash Filesystem.

M-Systems Disk-On-Chip

http://www.linux-mtd.infradead.org/doc2000.html

This is supported via the Memory Technology Device Subsystem.

11.3 PCMCIA Cards

For a PCMCIA driver, see: http://lists.linuxppc.org/listarcs/linuxppc-embedded/200002/msg00093.html

There are also some fairly detailed notes available at: ftp://ftp.absoval.com/pub/rpxlite/ and http://lists.linuxppc.org/listarcs/linuxppc-embedded/200005/msg00227.html

For generic Linux PCMCIA info, see: http://pcmcia.sourceforge.org/ftp/doc/PCMCIA-PROG.html

11.4 IDE/ATA Disk Drives

There are lots of options for connecting IDE drives. You need to at least configure CONFIG_BLK_DEV_IDE and CONFIG_BLK_DEV_IDEDISK. Search for IDE.

Also, see: http://www.bluebutton.com/proj/mbxlinux/.

11.5 PCI Bridge

Search for QSPAN or PowerSpan.

11.6 Watchdog

Using the on-chip watchdog to provide the basic "write kicked" /dev/watchdog interface described in Documentation/watchdog.txt is problematic, because the SYPCR register controlling it can only be written once after reset to both set the timeout and enable the watchdog. Once enabled, the boot loader and kernel must keep it from expiring up until the point where the user application opens /dev/watchdog. Littering the generic kernel decompress and startup code with watchdog kicks to do this isn't acceptable to other Linux users. Hence, hardware watchdog support hasn't been implemented yet.

The general plan to solve this problem is described in: http://lists.linuxppc.org/listarcs/linuxppc-embedded/199910/msg00026.html

You can probably use Linux's software watchdog in the mean time.

11.7 USB for MPC850/823

http://www.honeywell.se/inu/usb/ and http://lists.suse.com/archives/linux-usb/2000-Mar/0234.html

These devices can be made to operate as a USB host or slave. Search for USB.

Also see the Programming Guide for Linux USB Device Drivers at http://usb.in.tum.de/usbdoc/

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