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Chapter 16. PC Card
PC Card
This chapter will talk about the FreeBSD mechanisms for writing a device driver for a PC Card or CardBus device. However, at present it just documents how to add a new device to an existing pccard driver.
Adding a Device
Device drivers know what devices they support. There is a table of supported devices in the kernel that drivers use to attach to a device.
Overview Visión general
PC Cards are identified in one of two ways, both based on the _Card Information Structure_ (CIS) stored on the card. The first method is to use numeric manufacturer and product numbers. The second method is to use the human readable strings that are also contained in the CIS. The PC Card bus uses a centralized database and some macros to facilitate a design pattern to help the driver writer match devices to his driver.
Original equipment manufacturers (OEMs) often develop a reference design for a PC Card product, then sell this design to other companies to market. Those companies refine the design, market the product to their target audience or geographic area, and put their own name plate onto the card. The refinements to the physical card are typically very minor, if any changes are made at all. To strengthen their brand, these vendors place their company name in the human readable strings in the CIS space, but leave the manufacturer and product IDs unchanged.
Due to this practice, FreeBSD drivers usually rely on numeric IDs for device identification. Using numeric IDs and a centralized database complicates adding IDs and support for cards to the system. One must carefully check to see who really made the card, especially when it appears that the vendor who made the card might already have a different manufacturer ID listed in the central database. Linksys, D-Link, and NetGear are a number of US manufacturers of LAN hardware that often sell the same design. These same designs can be sold in Japan under names such as Buffalo and Corega. Often, these devices will all have the same manufacturer and product IDs.
The PC Card bus code keeps a central database of card information, but not which driver is associated with them, in [.filename]#/sys/dev/pccard/pccarddevs#. It also provides a set of macros that allow one to easily construct simple entries in the table the driver uses to claim devices.
Finally, some really low end devices do not contain manufacturer identification at all. These devices must be detected by matching the human readable CIS strings. While it would be nice if we did not need this method as a fallback, it is necessary for some very low end CD-ROM players and Ethernet cards. This method should generally be avoided, but a number of devices are listed in this section because they were added prior to the recognition of the OEM nature of the PC Card business. When adding new devices, prefer using the numeric method.
Format of [.filename]#pccarddevs#
There are four sections in the [.filename]#pccarddevs# files. The first section lists the manufacturer numbers for vendors that use them. This section is sorted in numerical order. The next section has all of the products that are used by these vendors, along with their product ID numbers and a description string. The description string typically is not used (instead we set the device's description based on the human readable CIS, even if we match on the numeric version). These two sections are then repeated for devices that use the string matching method. Finally, C-style comments enclosed in `/*` and `*/` characters are allowed anywhere in the file.
The first section of the file contains the vendor IDs. Please keep this list sorted in numeric order. Also, please coordinate changes to this file because we share it with NetBSD to help facilitate a common clearing house for this information. For example, here are the first few vendor IDs:
vendor FUJITSU 0x0004 Fujitsu Corporation
vendor NETGEAR_2 0x000b Netgear
vendor PANASONIC 0x0032 Matsushita Electric Industrial Co.
vendor SANDISK 0x0045 Sandisk Corporation
Chances are very good that the `NETGEAR_2` entry is really an OEM that NETGEAR purchased cards from and the author of support for those cards was unaware at the time that Netgear was using someone else's ID. These entries are fairly straightforward. The vendor keyword denotes the kind of line that this is, followed by the name of the vendor. This name will be repeated later in [.filename]#pccarddevs#, as well as used in the driver's match tables, so keep it short and a valid C identifier. A numeric ID in hex identifies the manufacturer. Do not add IDs of the form `0xffffffff` or `0xffff` because these are reserved IDs (the former is "no ID set" while the latter is sometimes seen in extremely poor quality cards to try to indicate "none"). Finally there is a string description of the company that makes the card. This string is not used in FreeBSD for anything but commentary purposes.
The second section of the file contains the products. As shown in this example, the format is similar to the vendor lines:
/* Allied Telesis K.K. */
product ALLIEDTELESIS LA_PCM 0x0002 Allied Telesis LA-PCM
/* Archos */
product ARCHOS ARC_ATAPI 0x0043 MiniCD
The `product` keyword is followed by the vendor name, repeated from above. This is followed by the product name, which is used by the driver and should be a valid C identifier, but may also start with a number. As with the vendors, the hex product ID for this card follows the same convention for `0xffffffff` and `0xffff`. Finally, there is a string description of the device itself. This string typically is not used in FreeBSD, since FreeBSD's pccard bus driver will construct a string from the human readable CIS entries, but it can be used in the rare cases where this is somehow insufficient. The products are in alphabetical order by manufacturer, then numerical order by product ID. They have a C comment before each manufacturer's entries and there is a blank line between entries.