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Technical Background for the Intel SL Microprocessor
-designed specifically for mobile computing
Abstract
What is the right microprocessor technology for mobile computers? Is it a fast desktop microprocessor? Do mobile computer users have requirements which are different from their desktops and do these requirements affect the design technology and features of the microprocessor? This paper will address these questions. It will also show why the Intel SL microprocessor is the right answer for mobile computers and how it enables mobile computers to reach a new level of functionality with the following features:
High integration for smaller and lighter systems
High performance for faster operation
Power management for longer battery life
Instant on/off for convenience
Smaller and Lighter Mobile Computers
Smaller and lighter rank high on the feature list which users want from their mobile computers. In fact, the typical user wants the mobile computer to be as small and light as possible as long as it does not become too small to type on or lacks other necessary features.
The Intel SL CPU enables smaller form factor mobile computers by using a very high level of integration. This means that few electronic components are needed to build the computer, and therefore, it can be smaller. The first generation 32 bit mobile computers were based on the Intel386 TM SX microprocessor. This processor was originally designed for desktop computing and had only 275k transistors. The Intel SL microprocessor has 855k transistors, or 3 times more. In addition, the Intel SL microprocessor has a companion I/O chip which implements the complete core logic I/O subsystem of the AT* standard. These two devices shrink the board space for comparable logic devices by as much as 40% when compared to the first generation systems. The system manufacturer can use this free space to build a smaller computer or to include many more features which users desire such as more memory, modem and FAX modem plug ins, LAN controllers, or ExCa TM card support.
The Intel SL CPU can also make a mobile computer smaller and lighter in another way. Because the power management features of the Intel SL make the battery last longer, the system manufacturers can also utilize a smaller and lighter battery.
Intel SL CPU Performance
Many mobile computer users like the performance which they have in their desktop system. They don't want to give up performance for mobility. They like their Windows and OS/2* operating systems and they want their applications to run fast on these powerful OS's. The Intel SL microprocessor was designed with performance in mind by offering 25 MHz speed and supporting up to a 64k zero wait state cache memory with its on chip cache memory controller.
Most first generation mobile computers provided little or no cache memory. Compared to the first generation of 32 bit mobile computers, the Intel SL based systems are typically 20% faster. This performance comparison is best shown by looking at the following common benchmarks.
The Intel SL CPU has yet other features which give it high performance. The Intel SL CPU has implemented an Extended Memory Controller (EMS) in hardware which is 1.7x faster than a typical software driver implementation.
Intel SL Power Management for Longer Battery Life
How is battery life measured? How does power management affect it? Battery life is simply how long the mobile computer lasts while in typical use operating on battery power. For most users, typical mobile computer use is not one long lasting session which is conducted until the battery runs down. After all, if the user is stationary in one location for a long period of time, wall power may be available. Mobile computer use is a mix of both short frequently interrupted use and longer term use. One commonly cited example of mobile computer use is during air travel. Even during long distance travel, mobile computer use is interrupted by boarding, taking off and landing, meals, and user fatigue.
To get longer battery life, the mobile computer must use the battery efficiently --delivering power only on demand. Each component of the mobile computer (disk drives, screen, CPU , I/O , other peripherals, and memory) consumes part of the battery's power budget. The Intel SL has a built in power management system which powers these components efficiently. For example, when you are entering data, the disk drives, modems, and other peripheral circuitry can be powered off until they are needed. If you pause for a period of time, the LCD screen, backlight, and other electronics can be powered off. For longer delays, the Intel SL based mobile computer can be put into the suspend or sleep state where power consumption is extremely low.
Earlier generation mobile computers which were designed with the Intel386TM SX
microprocessor did not have built in power management. The power management had to be added with external circuitry which is not as efficient and also consumes more space. To demonstrate the improvement in power management provided by the Intel SL CPU, an independent test was conducted on two commonly available mobile computers. One was designed with the Intel386TM SX CPU and the other was designed with the Intel SL CPU. The battery capacity and power consumption of the two systems were nearly identical. The results are shown on the next page.
This test was designed to represent typical mobile computer use. First, a "user profile" of real world applications including Microsoft Windows*, Word, and Excel was executed on both systems with power management disabled. The results show that the Intel SL system was slightly better than the SX system lasting 2.73 hours vs. 2.47 hours. In the second test, power management was enabled in both systems. The Intel SL power management stretched the battery life 4.85 additional hours vs. 2.6 additional hours for the SX system. The Intel SL CPU power management stretched the battery life nearly twice as long.
Power Management without Software Conflicts
First generation power management often conflicted with operating system and applications programs, leading to system glitches or worse, lost data. Software manuals were filled with warnings and cautions about these problems:
"Caution: If you use the Standby button when running some applications, the program may fail."
"CPU sleep mode may cause some programs...to malfunction."
"Caution: Before running OS/2..(disable the power management.) Otherwise, execution errors will occur because the operating system does not give the hard-disk drive enough time to spin up when accessing it for data."
"The (unit) may not operate correctly if you enable (suspend) and run software that directly addresses the hardware...(for example, Windows 386)."
With first generation systems, the applications software and operating system were unaware that peripheral devices and even the CPU had been turned off during power management. System manufacturers tried to solve these problems by supplying software drivers or custom versions of the operating system, but even then, the chances for failure still existed. Realizing the problems, some manufactures greatly limited the amount of power management in the mobile computer in order to avoid them.
To provide a solid solution, Intel designed a new power management architecture into the Intel SL CPU called Intel System Management Mode (SMM). This is a completely new mode of operation which is totally isolated and independent from other CPU hardware and software. Intel SMM provides hardware resources such as timers, registers, and other I/O logic which can control and power down mobile computer components without interfering with any of the other system resources. Intel SMM software executes in a dedicated memory space called System Management Memory which is not visible and does not interfere with operating system and applications software. Intel SMM has a new interrupt called System Management Interrupt which services power management events and is independent and higher priority than any of the other interrupts. Finally, Intel SMM provides power levels for the Intel SL CPU and I/O which are much lower than those found in other implementations.
Intel System Management Mode provides power management with the flexibility and security not previously available. For example, when an applications program tries to access a peripheral device which is powered down for battery savings, a System Management Interrupt occurs which powers up the peripheral device and re-executes the I/O instruction automatically. In addition, since the Intel SMM can save and restore complete system status reliably, the mobile computer manufacturer is not forced to compromise and leave circuitry powered because status cannot be recovered.
This flexibility in power management encourages broader innovation, too. Designers can use the conserved power to support more features such as brighter screens, increased resolution, color, stylus, and new communications options.
With the Intel SL CPU's transparent power management, computer manufacturers can offer a no compromise mobile computer which is compatible with desktop computers. Mobile computers can run the latest operating system, GUI's and applications programs while conserving power. With the Intel SL icroprocessor, mobile computer users can work longer and more productively, with fewer inconvenient battery recharges, lost time, and lost work.
Instant On/Off for User Convenience
The demands on a mobile computer are greater in some areas than those on a desktop computer. When users are interrupted and leave their desktop computer, they expect to return to it later with everything intact. They don't even think about closing all of the running software and powering it down every time they are interrupted or walk away. However, the need to stop, power down, power up, and start a mobile computer is a fact of life. Intel designed the Intel SL with this in mind by providing a feature called suspend/resume. The system manufacturer may use this feature to provide the mobile computer user with "Instant On/Off". Because an Intel SL mobile computer can resume or "Instant on" typically in one second from the suspend or "Off" state to exactly where it was left, the computer is available over long periods of time with frequent interruptions. There is no need to reboot, load the operating system, load the application program, and then load applications data. Simply push the suspend/resume button and the system is ready to go. Of course, this does not eliminate the need to regularly save data to disk and back it up -- but with an Intel SL mobile computer there is no need to constantly save everything away every time there is an interruption.
So why go into the suspend state in the first place? The Intel SL CPU was designed to consume almost no power while in the suspend state. In other words, the Intel SL system can stay in the suspend state sometimes for weeks and yet start instantly right it stopped. This feature not only provides convenience, but also provides security for working data. While in the suspend state, an Intel SL system can keep working data in volatile RAM memory safe for a long time. A comparison between typical Intel SL and 386 SX based systems is shown in the graphs below. The best 386 SX system would keep data in the lowest power consuming state of the machine for a day -- many systems keep it for a shorter period. A typical Intel SL system, however, can keep data in the suspend state for 2 weeks. For example, if there were 15 minutes of battery life remaining, the 386 SX notebook would last for 2.75 hours in the suspended state and the Intel SL notebook would last another 24 hours. Some Intel SL systems go even one step further. When these systems notice that they have been in suspend for a long period of time (for example 15 minutes) they save all of system memory to disk or flash memory and turn themselves completely off -- saving data permanently. Of course, resuming in this case takes longer (15 seconds typically) since memory must be replaced from the disk.