Writing Device Drivers

Walking the PROMs Device Tree

The SunOS-like commands pwd, cd, and ls walk the PROM device tree to get to the device. The cd command must be used to establish a position in the tree before pwd will work. This example is from an Ultra-1 workstation with a cgsix frame buffer on an SBus.

ok cd /

To see the devices attached to the current node in the tree, use ls.

ok lsf006a064 SUNW,UltraSPARC@0,0
f00598b0 sbus@1f,0
f00592dc counter-timer@1f,3c00
f004eec8 virtual-memory
f004e8e8 memory@0,0
f002ca28 aliases
f002c9b8 options
f002c880 openprom
f002c814 chosen
f002c7a4 packages

The full node name can be used:

ok cd sbus@1f,0ok lsf006a4e4 cgsix@2,0
f0068194 SUNW,bpp@e,c800000
f0065370 ledma@e,8400010
f006120c espdma@e,8400000
f005a448 SUNW,pll@f,1304000
f005a394 sc@f,1300000
f005a24c zs@f,1000000
f005a174 zs@f,1100000
f005a0c0 eeprom@f,1200000
f0059f8c SUNW,fdtwo@f,1400000
f0059ec4 flashprom@f,0
f0059e34 auxio@f,1900000
f0059d28 SUNW,CS4231@d,c000000

Rather than using the full node name in the previous example, you could have used an abbreviation. The abbreviated command line entry looks like this:

ok cd sbus

The name is actually device@slot,offset (for SBus devices). The cgsix device is in slot 2 and starts at offset 0. If an SBus device is displayed in this tree, the device has been recognized by the PROM.

The.properties command displays the PROM properties of a device. These can be examined to determine which properties the device exports (this is useful later to ensure that the driver is looking for the correct hardware properties). These are the same properties that can be retrieved with ddi_getprop(9F). See sbus(4) and "Properties" for related information.

ok cd cgsixok .propertiescharacter-set            ISO8859-1
intr                     00000005 00000000
interrupts               00000005
reg                      00000002 00000000 01000000
dblbuf                   00 00 00 00
vmsize                   00 00 00 01

The reg property defines an array of register description structures containing the following fields:

	u_int		bustype;					/* cookie for related bus type*/
 	u_int		addr;					/* address of reg relative to bus */
 	u_int		size;					/* size of this register set */

For the cgsix example, the address is 0.