Mobile Computing with Linux

Power management is not really supported under Linux. Based on the Linux Laptop Survey results, a laptop running Linux will typically last for two hours on batteries. Although an APM support package does exist, it only provides the initial hooks into the APM BIOS for power management. At this point the APM support just recognizes when the system returns from sleep mode and updates the internal clock, which is important to keep the system sane. APM applications that display the current battery level and execute the “shutdown” command when the battery runs low are also available. This software may be retrieved from tsx-11:/pub/linux/ packages/laptops/apm.

As mentioned earlier, the SL processor series has SMM features to power manage the processor. However, a portable power management solution that doesn't require SMM support is to halt the processor in the scheduler's idle loop. The x86 asm(hlt) instruction suspends the processor until there is an interrupt from the system (e.g. a key stroke). Linux versions above v1.1.10 implement this simple and effective solution, which does not degrade performance at all. It has the added benefit (even to non-laptop users) of increasing the expected life of your CPU.

PCMCIA provides plug-and-play capabilities to the laptop. Currently support exists for the Intel 82365 adaptor chip, PCMCIA modems (Megahertz, IBM, Intel, AT&T, and others), and ethernet cards (D-Link 650, Linksys, IBM credit card, and 3COM 3c589). The PCMCIA support in Linux is still in its alpha stages and is available from tsx-11:/pub/linux/packages/laptops/pcmcia. PCMCIA support that meets the PCMCIA Unix specification is in the works and you may expect it to be part of the standard Linux distribution by the end of the year.

A future article will discuss operating system implications of mobile computers.

F. Douglis and B. Marsh, Low-Power Disk Management for Mobile Computers, Matsushita Information Technology Lab, 2 Research Way, Third Floor, Princeton, NJ, 1993, MITL-TR-53-93

Fred Douglis and P. Krishnan and Brian Marsh, Thwarting the Power-Hungry Disk, Proceedings of the 1994 Winter USENIX Conference, January 1994, (Also Matsushita Information Technology Lab Technical Report MITL-TR-61-93)

Proceedings of the 1994 Winter USENIX Conference, January 1994