1The `parport' code provides parallel-port support under Linux. This 2includes the ability to share one port between multiple device 3drivers. 4 5You can pass parameters to the parport code to override its automatic 6detection of your hardware. This is particularly useful if you want 7to use IRQs, since in general these can't be autoprobed successfully. 8By default IRQs are not used even if they _can_ be probed. This is 9because there are a lot of people using the same IRQ for their 10parallel port and a sound card or network card. 11 12The parport code is split into two parts: generic (which deals with 13port-sharing) and architecture-dependent (which deals with actually 14using the port). 15 16 17Parport as modules 18================== 19 20If you load the parport code as a module, say 21 22 # insmod parport.o 23 24to load the generic parport code. You then must load the 25architecture-dependent code with (for example): 26 27 # insmod parport_pc.o io=0x3bc,0x378,0x278 irq=none,7,auto 28 29to tell the parport code that you want three PC-style ports, one at 300x3bc with no IRQ, one at 0x378 using IRQ 7, and one at 0x278 with an 31auto-detected IRQ. Currently, PC-style (parport_pc) and Sun Ultra/AX 32(parport_ax) hardware is supported; more is in the works. 33 34 35KMod 36---- 37 38If you use kmod, you will find it useful to edit /etc/conf.modules. 39Here is an example of the lines that need to be added: 40 41 alias parport_lowlevel parport_pc 42 options parport_pc io=0x378,0x278 irq=7,auto 43 44KMod will then automatically load parport_pc (with the options 45"io=0x378,0x278 irq=7,auto") whenever a parallel port device driver 46(such as lp) is loaded. 47 48 49Parport probe [optional] 50------------- 51 52Once the architecture-dependent part of the parport code is loaded 53into the kernel, you can insert the parport_probe module with: 54 55 # insmod parport_probe.o 56 57This will perform an IEEE1284 probe of any attached devices and log a 58message similar to: 59 60 parport0: Printer, BJC-210 (Canon) 61 62(If you are using kmod and have configured parport_probe as a module, 63this will just happen.) 64 65The probe information is available in /proc/parport/?/autoprobe. 66 67 68Parport linked into the kernel statically 69========================================= 70 71If you compile the parport code into the kernel, then you can use 72kernel boot parameters to get the same effect. Add something like the 73following to your LILO command line: 74 75 parport=0x3bc parport=0x378,7 parport=0x278,auto 76 77You can have many `parport=...' statements, one for each port you want 78to add. Adding `parport=0' to the kernel command-line will disable 79parport support entirely. Adding `parport=auto' to the kernel 80command-line will make parport use any IRQ lines or DMA channels that 81it auto-detects. 82 83 84Files in /proc 85============== 86 87If you have configured the /proc filesystem into your kernel, you will 88see a new directory entry: /proc/parport. In there will be a 89directory entry for each parallel port for which parport is 90configured. In each of those directories are four files describing 91that parallel port. For example: 92 93File: Contents: 94 95/proc/parport/0/devices A list of the device drivers using 96 that port. A "+" will appear by the 97 name of the device currently using the 98 port (it might not appear against any). 99 100/proc/parport/0/hardware Parallel port's base address, IRQ line 101 and DMA channel. 102 103/proc/parport/0/irq The IRQ that parport is using for that 104 port. This is in a separate file to 105 allow you to alter it by writing a new 106 value in (IRQ number or "none"). 107 108/proc/parport/0/autoprobe Any IEEE-1284 device ID information 109 that has been acquired. 110 111 112Device drivers 113============== 114 115Once the parport code is initialised, you can attach device drivers to 116specific ports. Normally this happens automatically; if the lp driver 117is loaded it will create one lp device for each port found. You can 118override this, though, by using parameters either when you load the lp 119driver: 120 121 # insmod lp.o parport=0,2 122 123or on the LILO command line: 124 125 lp=parport0 lp=parport2 126 127Both the above examples would inform lp that you want /dev/lp0 to be 128the first parallel port, and /dev/lp1 to be the _third_ parallel port, 129with no lp device associated with the second port (parport1). Note 130that this is different to the way older kernels worked; there used to 131be a static association between the I/O port address and the device 132name, so /dev/lp0 was always the port at 0x3bc. This is no longer the 133case - if you only have one port, it will default to being /dev/lp0, 134regardless of base address. 135 136Also: 137 138 * If you selected the IEEE-1284 autoprobe at compile time, you can say 139 `lp=auto' on the kernel command line, and lp will create devices 140 only for those ports that seem to have printers attached. 141 142 * If you give PLIP the `timid' parameter, either with `plip=timid' on 143 the command line, or with `insmod plip timid=1' when using modules, 144 it will avoid any ports that seem to be in use by other devices. 145 146 * IRQ autoprobing works only for a few port types at the moment. 147 148-- 149Philip.Blundell@pobox.com 150tim@cyberelk.demon.co.uk 151