Touchpad/Testing
Touchpad calibration and testing is a complex area, not very well documented in the industry. This page collects useful information when testing and debugging touchpads.
OLPC has shipped 3 touchpads:
- Sentelic AVC Finger Sensing Pad (in XO-1 CL1A model, XO-1.5, XO-1.75, XO-4),
- Synaptics touchpad (in XO-1 CL1A model, XO-1.5, XO-1.75), and;
- ALPS full width three panel touchpad (in XO-1 CL1 model).
Contents
Identification
In Terminal activity, type this:
cat /sys/bus/serio/drivers/psmouse/serio*/protocol
The value displayed is the protocol of the communication link between the computer and the touchpad. Possible values include:
- FSPPS/2 - Sentelic AVC Finger Sensing Pad,
- SynRelPS/2 - Synaptics touchpad, in relative mode, on latest kernel,
- SynPS/2 - Synaptics touchpad, in Synaptics protocol mode, on a previous kernel,
- OLPC HGPK - ALPS full width three panel touchpad.
Also, look at the boot messages, type this:
cat /sys/bus/serio/drivers/psmouse/serio*/protocol && \ dmesg | grep psmouse
Example output, 13.2.0 on XO-4 with Sentelic touchpad:
FSPPS/2 [ 11.001718] psmouse serio1: sentelic: Finger Sensing Pad, hw: 13.2.6, sn: 0, sw: 1.1.0-K
Example output, 13.2.0 on XO-1.75 with Sentelic touchpad:
FSPPS/2 [ 8.937258] psmouse serio1: ID: 10 02 64
Example output, 13.2.0 on XO-1.5 with Synaptics short touchpad:
SynRelPS/2 [ 15.804359] psmouse serio1: synaptics: OLPC XO detected, not enabling Synaptics protocol. [ 19.228099] psmouse serio1: synaptics: Touchpad model: 1, fw: 6.2, id: 0x92a0b1, caps: 0xa04711/0x200000/0x0
Example output, 13.2.0 on XO-1 with Synaptics short touchpad:
SynRelPS/2 [ 16.447317] psmouse serio1: synaptics: OLPC XO detected, not enabling Synaptics protocol. [ 18.583646] psmouse serio1: synaptics: Touchpad model: 1, fw: 6.2, id: 0x92a0b1, caps: 0xa04711/0x200000/0x0
Example output, 13.2.0 on XO-1 with ALPS full width three panel touchpad:
OLPC HGPK [ 17.001941] psmouse serio1: hgpk: ID: 67 00 50 [ 17.001963] psmouse serio1: hgpk: OLPC touchpad revision 0x50
Variables
These are the variables we find influence TP performance. Our tuning work aims to find a good balance that makes the TP work correctly for a wide range of cases.
Keep in mind that these variables can be pushed to points where the TP misbehaves -- make your finger wet enough, or your power source dirty enough, and no TP will work correctly regardless of vendor and tuning.
Experience indicates that configuration changes that consider only a subset of these variables... are going to break some of the untested cases.
- Dirty power: if the power supply is connected to a dirty/noisy power strip (ie: one with several other power supplies connected), this can cause issues with the TP input; control for this by also testing on battery power.
- Battery charging: when on external power, whether the battery is charging or not may influence behaviour. Control for this by testing with a discharged battery, as well as without a battery.
- Approach speed: some TPs calibrate as soon as they sense the finger on the TP -- if your finger approaches the TP very slowly, the calibration loop might catch signal of your finger near, but not in contact with the TP, leading to erratic tracking; control for this with very slow approach to the TP as well as fast & firm approach to the TP.
- Firmness of touch: very light contact with the TP can lead to erratic tracking; control for this using a very light touch, as well as firm contact with the TP.
- Hand placement: the ideal condition for the TP is where only one finger contacts the laptop; so try
- strictly one finger
- second hand holding the unit near the antennas / speakers
- second hand holding the corner of the base assembly
- second hand under the base assembly, under the touchpad area
- second hand near (but not touching) touchpad
- thumb resting on buttons
- Lap vs table: body contact /proximity with the laptop can affect TP behaviour -- test with the laptop on your lap, then on a plastic or wooden table.
- Humidity and temperature: test in hot+humid, hot+dry, cold+humid, cold+dry environments; the top risk is hot+humid.
- Dust and humidity: dust, specially combined with humidity, poses a hard problem for TPs, test with talcum powder in a humid environment.
- Sweaty/wet finger: a drop of water or a wet finger are expected to confuse TPs. Sweaty fingers are a hard problem for TPs but should be able to operate passably.
- Finger size: different finger sizes look very different to the TP software -- test with users with various finger sizes. Ensure you test with children!
- User variation: Other variations in users bodies and usage patters can affect the TP. Ensure you test with a number of users.
Tests
Standing finger
- Place your finger in one spot, keep it there for at least one minute. The pointer should not move.
This test is useful to reveal very dirty power sources.
Circles
- Put your finger on the TP and move the pointer in circles -- for example follow the Sugar Activity icons circle/spiral loosely for at least one minute.
- Optionally, try to finish the stroke pointing to a specific icon or element on screen.
After a few seconds, a faulty TP will start tracking the circle motion erratically.
Rolling finger
- Place your finger in one spot of the TP, in a 45 degree angle
- Without lifting the finger, roll it left and right repeatedly, for at least 1 minute
After a few seconds of finger rolling, a faulty TP will start reporting erratic position jumps.
This test exercises the small finger motions used for precise pointer movements.
Spirals
- Paint spirals from the outside in, trying to avoid crossing an already-painted line.
This is a good test for precision.
Corner to corner sweep
- Move the pointer to a corner of the screen
- In one fast stroke, you should be able to reach the opposite corner of the screen.
This test controls for acceleration -- ideally the configured acceleration allows you to both have precision with slow movements, and enough accel that swift movements can cover the whole screen corner-to-corner distance.
