Linux Device Drivers, Second Edition

Other PC Buses

PCI and ISA are the most commonly used peripheral interfaces in the PC world, but they aren’t the only ones. Here’s a summary of the features of other buses found in the PC market.

MCA

Micro Channel Architecture (MCA) is an IBM standard used in PS/2 computers and some laptops. The main problem with Micro Channel is the lack of documentation, which has resulted in a lack of Linux support for MCA up until recently.

At the hardware level, Micro Channel has more features than ISA. It supports multimaster DMA, 32-bit address and data lines, shared interrupt lines, and geographical addressing to access per-board configuration registers. Such registers are called Programmable Option Select, or POS, but they don’t have all the features of the PCI registers. Linux support for Micro Channel includes functions that are exported to modules.

A device driver can read the integer value MCA_bus to see if it is running on a Micro Channel computer, similar to how it uses pci_present if it’s interested in PCI support. If the symbol is a preprocessor macro, the macro MCA_bus__is_a_macro is defined as well. If MCA_bus__is_a_macro is undefined, then MCA_bus is an integer variable exported to modularized code. Both MCA_BUS and MCA_bus__is_a_macro are defined in <asm/processor.h>.

EISA

The Extended ISA (EISA) bus is a 32-bit extension to ISA, with a compatible interface connector; ISA device boards can be plugged into an EISA connector. The additional wires are routed under the ...