Writing PCMCIA/CF Device Drivers
Technologies like Wi-Fi, GPRS, and miniature storage devices are ubiquitous today as PCMCIA or CF cards. The Linux kernel supports PCMCIA devices on a variety of architectures.
Much of today’s popular technologies, such as memory cards, modems, wireless and wired Ethernet, General Packet Radio Service (GPRS), and the Global Positioning System (GPS) are widely available in the form factor of PCMCIA (an acronym for Personal Computer Memory Card International Association) or Compact Flash (CF) cards. Most laptops and many embedded devices support PCMCIA or CF interfaces, thus instantly enabling them to make use of a wide variety of technologies.
PCMCIA is a 16-bit data transfer interface specification that uses the 68-pin connector originally used by memory cards. The specification has grown to include support for higher speeds in the form of 32-bit CardBus cards. (The term PC Card is used when referring to either PCMCIA or CardBus devices.) CF cards are smaller, but compatible with PCMCIA, and are frequently used in handheld devices like PDAs and digital cameras. CF cards come in two flavors: Type 1 cards and the thicker Type II cards. CF cards have only 50 pins, but can be slipped into your laptop’s PCMCIA slot using a passive CF-to-PCMCIA adapter.
In this column, let’s explore how the Linux PCMCIA layer works and examine the support present in the kernel for PCMCIA/CF host adapters and client devices. Next month’s column will use the concepts learned here while implementing simple drivers for some popular networking and storage technologies.
The Kernel PCMCIA/CF Layer
