Embedded controller

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Contents

Introduction

The XO laptop uses a small micro-controller, an ENE KB3700 (Datasheet), to control the battery charging operation and perform other tasks associated with starting and stopping the laptop.

This Embedded Controller (EC) consists of a 8051 micro-controller, a dedicated LPC interface to communicate with the processor, and an SPI Flash ROM interface. The SPI Flash ROM supports two code segments, and a table of Manufacturing Data. The EC supports the Boot Hub Protocol, allowing the XO's main processor to boot from one of the code segments in the SPI Flash.

Details

The EC, implemented as a KB3700, has a paramount importance in controlling the XO when the CPU is not active. To do so, the KB3700 communicates with the CPU via the EC protocol over a physical LPC interface. For more information, see the Ec specification.

The KB3700 also communicates with the Maxim DS2756 battery fuel gauge IC within the battery pack, via the 1-wire Dallas protocol. DS2756 data sheet.

ec-status

One can deduce part of the internal state of the EC using ec-dump.fth under Open Firmware. Running the ec-dump script gives us valuable data about internals of the EC, being the EC Register Settings.

The procedure to run ec-dump over internet in a wireless connection is:

ok wifi media lab 802.11 *change it to your name AP
ok fl http:\\18.85.2.147\~joel\ec-dump.fth *change to your AP IP direction

Running ec-dump over internet and saving the file in a USB key:

ok wifi media lab 802.11 *change it to your name AP
ok fload http:\\18.85.2.147\~rafael\to-file.fth
ok to-file u:\ec-dump fload http:\\18.85.2.147\~joel\ec-dump.fth

OpenEC firmware project

The firmware running on the XO's EC, while heavily modified and supported by OLPC, was originally written by two different companies. OLPC has had no success convincing those companies to open source their code.

The OLPC community is now working on OpenEC, an Open Source implementation of the XO's Embedded Controller firmware. It currently is in an early stage and not functional yet.

Related Documentation

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