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Administración de potencia

Introducción y material relacionado

Careful stewardship of battery power is critical.

Esta pagina es un trabajo en proceso que recopila información relacionada a la administración de potencia de OLPC.

• Hardware Power Domains
• Power Management Software
• XO Power Management Tips and Tricks
• Misc. Papers on Energy Efficiency in Computing and Networking

Ademas de manejar efectivamente la potencia que hay en la batería también la pagina Battery and power discute muchas fuentes alternas de potencia que pueden ser usadas para complementar el actual cargador.

Enfoque de Linux al control de potencia

Linux es una plataforma altamente portable que corre en casi todas las arquitecturas importantes, incluso muchas que son usadas para sistemas embebidos que utilizan baterías. Por ello la infraestructura para manejo de potencia se ha vuelto algo sofisticada en los últimos años, aunque aun esta madurando. Esto significa que las instalaciones son generales y no estan atadas a una arquitectura particular. La primera generación del sistema OLPC, siendo de la parte x86 del mundo es por ello similar y fundamentalmente diferente de otros sistemas basados en x86, por razones que seran claras en la siguiente discusión.

Linux no es dependiente de ACPI o los mas viejos sistemas de administración de potencia APM, que son específicos para x86. Por ello, el diseño de Linux ha siempre hecho su control de potencia en el sistema operativo, y ACPI u otros parecidos son considerados "dependientes de la plataforma".

Innovaciones de OLPC

El chip DCON nos deja manejar el refresco de nuestro "flat panel" de bajo consumo de potencia y por ello apagar completamente la board del procesador. Dado que nuestro "flat panel" es usable en modo de escala de grises a 1 vatio, usted puede ver que las corrientes de fuga (leakage) y el consumo de potencia de la fuente de poder pueden dominar el consumo de potencia fácilmente. Podemos también ser capaces de dejar que el modulo wireless de Marvell opere independientemente, mandando paquetes por la Mesh mientras que posiblemente todo lo demás este apagado.

Firmware (BIOS en PC's convencionales)

Uso del Open Firmware

Rather than using a conventional BIOS and boot loader, as of the "C" series of our firmware we are using Open Firmware. We no longer use LinuxBIOS for the setup of our systems. This is a result of having implemented fast past resume from RAM; once you have implemented this, setup of the system initially is almost identical.

We have also removed VSA and VESA support (the Geode Virtual Systems Support) from our firmware. Since our PCI bus is fixed, we have no need for PCI configuration registers. Similarly, using the fbdev driver on Linux, we have no need for VESA emulation; while the PCI bus emulation was free software (AMD had generously made it available), the VESA emulation was the one part of VSA that they did not own, and so we did not have source for it. We did not want an unmaintainable binary blob in our firmware that we did not need anyway, and saves space in the flash for other purposes.

Fast Resume

Resume on our system is extremely fast: even without any serious attempt to optimize resume, we can resume from RAM in 160 milliseconds (mid-April). We believe the hardware limitations for resume are about 63 milliseconds on the B2 and before systems; B3 and later are probably similar. We will work in the future to further speed resume. Note that for most uses, 100ms is considered at the edge of human perception (e.g. typing).

Identificación del sistema

The Manufacturing Data page documents the Model ID string, part number, localization information, factory, BIOS version, and many other pieces of data.

Quiet Boot

Boot is not "quiet" at this time. Linux has facilities to make a splash screen at boot overlay the boot messages, but OLPC has not implemented this as yet. Bug #1394 tracks this issue for eventual resolution.

POST Message

At this moment (prior to Q2C10, at a minimum), if any key is pressed during the initial countdown after the initial message, the boot sequence is stopped and OFW's command interpreter invoked. OFW gives a cheery "ok" message to indicate it is ready for a command.

Open Firmware Command Prompt

The OFW FAQ answers some of the most common questions of how to interact with the OLPC OFW firmware.

Power Management Support

As discussed above, Linux does not depend on ACPI. To meet our fast resume goals and transparency into the firmware, we do not use ACPI, which would significantly slow our resume from suspend while adding no benefit. In this regard, we differ significantly from other x86 systems. This is the normal case for Linux on other architectures, so should not be regarded as unusual for Linux overall.

Botón de Prendido/Apagado

The power button on OLPC serves as a power button.

Momentary Button Push

The system will suspend to RAM after the button is pressed momentarily. Wireless will be left operational when suspended this way. (Prior to deployment of suspend/resume, this button currently performs a clean Linux shutdown). See bug #1396 for more information.

Four Second Button Push

Pressing the power button for four seconds does a hard reset of the system and all state is lost.

Estados de Administración de Potencia

The following are the major operating states of the system. For simplicity's sake in using commonly understood terminology, see Wikipedia's ACPI article.

Powered Down

In this state, (G3 is this state in ACPI). Everything is off and the battery can be swapped. The operating system will have to be booted to start operation; the RAM is not preserved. On our hardware, if power is available, the EC will be powered up and potentially charging the battery.

Suspended, with Mesh Active, No screen

A common mode of use will be the system not being used, but still active forwarding in the mesh network on behalf of others in the mesh, but otherwise unused. This differs from our powered down state by the fact the Marvell wireless will be powered up, and active. In ACPI terminology, the closest match is G1/S3. The processor is suspended to RAM (in self-refresh).

Suspended, with Mesh Active, Screen Enabled

Another common mode of use is sometimes called "ebook mode". Both the screen and the Marvell wireless are left operational: the screen by use of the DCON chip. This differs from our powered down state by the fact the Marvell wireless will be powered up, and active along with the display. In ACPI terminology, the closest match is G1/S3. The processor is suspended to RAM (in self-refresh). Note that the DCON has facilities to implement a "screen saver" where it can disable itself and the backlight after a preset time without requiring the system to be resumed from RAM.

System fully operational

In this state, the system is available for normal use. The ACPI processor states that this corresponds to are C0 and C1 (note that C1 is not useful on a GX, but does save power on the LX). Linux is working very hard to remove "ticks"; as of this writing, the kernel is now "tickless" and this is operational on OLPC, meaning that it no longer uses a periodic timer clock interrupt to drive the scheduling of processes (which had caused 250 interrupts and transitions from C1 to C0 per second). The OLPC has been observed at 40 per second. Work is underway in user space to abolish polling of hardware that might force wakeups, and private communications are that a full Gnome environment has been seen as low as only a few wakeups/second.

Note that in this state, Linux may have many parts of the system powered down: e.g. audio, GPU, etc. as described in detail below.

Special Function Keys

System Management BIOS Interface

Not Supported