XO3 Tinderbox Power

This page describes the Tinderbox version of the XO-3 A1 tablet.

Power Distribution

The following diagram attempts to illustrate the XO-3 power distribution network, as well as the tinderbox measurement points:

Measurement Points

There are two types of measurement point in the above diagram. Most measure power passing through a particular point in the power distribution network, and are represented by a large X, along with an annotation of the voltmeter channel and measurement resistance. All measurement resistors have a tolerance (variation in resistance) of 1% or smaller.

A smaller number of points (3005, 3010) measure the voltage at a particular point in the power network. These are indicated by an arrow, and annotated solely with the voltmeter channel.

The definitive file describing this setup is the tinderbox configuration file.

Many of the system components are similar to those in the XO-1.75 laptop, and have been documented in the XO-1.75 Tinderbox.

Example Measurements

Example readings taken using this setup are available at http://dev.laptop.org/~wad/cl3_a1/. Some of these measurements are highlighted below.

Measurement Error

It should be cautioned that using a multiplexed voltmeter for measurement of power in a dynamic system has its downsides.

Off Power

TBD

Suspend Power

TBD

Display Power

Running the display (without the backlight) consumes 755 mW (not counting some inefficiencies in the power distribution network). This is broken down into:

XO-3 A1 Display Power

Frame memory	75 mW
MMP2 Display Ctrl.	180 mW
LVDS converter	152 mW
LCD Module	348 mW
Total	755 mW

The display backlight takes between 0 and 1.9 W to operate.

Using OFW

The ofw_nodisp.html file was generated using OFW. After booting the system into OFW, issue the following commands:

screen-ih iselect sleep  # turns off the display
backlight-off
d# 129 gpio-clr  # turn off display digital power
d# 33 gpio-clr    # turn off display analog power
d# 138 gpio-clr  # just make sure (in case the ECO doesn't work)

This both stops the frame buffer in the SoC and disables power to the external components (DCON and LCD module). This file was compared with ofw_idle.html to obtain the above numbers.

Using Linux

The first attempt at measuring the power consumed by the display was to force the screen to blank using:

echo 1 > /sys/devices/platform/pxa168-fb.0/graphics/fb0/blank

The results can be seen at linux_nodisp.html. They show that no external components were powered down, as well as no reduction in power consumed by the SoC (compare it to linux_idle.html) which we expect to see. The backlight power is weird as well...

USB ULPI Interface

The idle power consumption of this interface is around 15 mW (Idle).

Full power measurements to come