CEVA hillcrestlabs FSM300 Parts list manual

June 2017 Document 1000-4126 - FSM300 Tare Function Usage Guide - Revision 1.1
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FSM300
Tare Function Usage Guide
Introduction*
This document describes the Tare function of the FSM300 that redefines the orientation of the sensor.
This allows the outputs of the FSM300 to be in line with the orientation with which it was mounted into
the main device. These commands are described in more detail in the SH-2 Reference Manual [1] and
this document assumes that the reader has this manual available for reference.
Tare*Overview*
The FSM300 uses two commands and a configuration record to redefine the sensor’s orientation, or
“Tare”:
- Commands:
o Tare Now (Section 6.4.4.1 of SH-2 Reference Manual)
§ Allows for a temporary Tare. Useful at the start of a game to define the current
orientation.
o Persist Tare (Section 6.4.4.2 of SH-2 Reference Manual)
§ Saves the current Tare orientation into the Sensor Orientation configuration
record. This is a persistent setting that now becomes the default orientation.
- Configuration Record
o Sensor Orientation
§ Stores the orientation of the device. Once you know the standard orientation of
your FSM300 in your device, you can use the same starting orientation for all
devices using this record as a convenient starting point. More accurate per-
device taring can be done using the commands above.
Tare*Options*
There are two options that you can choose from when running a Tare operation:
- Axes
o Which axes do you want to tare across? For instance, you can choose to only tare on
yaw (Z-axis) which will reset the heading to the user’s current forward orientation. Or
you can tare across all axes (resets heading, pitch and roll).
- Rotation Vector to use as basis for Tare (Rotation Vector, Game Rotation Vector, Geomagnetic
Rotation Vector)
o The FSM300 offers three different types of Rotation Vector outputs that define the
orientation of the module using different inputs. Refer to the SH-2 Reference Manual
for more details about these three rotation vector options.

June 2017 Document 1000-4126 - FSM300 Tare Function Usage Guide - Revision 1.1
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o This Tare setting allows the user to choose which of the rotation vector outputs to use
as the basis for the Tare. In most cases, Rotation Vector is the correct choice here. If
you are using the Game Rotation Vector as your main input, and you want to tare the Z
rotation to re-center the Game Rotation Vector to point north, then you’d need to use
the Game Rotation Vector as the basis for the tare. Likewise, if you were doing a full
tare using the Geomagnetic Rotation Vector, then you would need to use that as the
basis.
Tare*Procedure*
Using the options defined above, you can choose what type of tare configuration makes the most sense
for your application. Here are a few examples of typical configurations:
Device First Time Setup
In this example, the FSM300 is installed in an HMD and the sensor orientation needs to be
defined. This could be performed at the factory or by the user at first time setup. This will use a full tare
across all 3 axes and also save the setting into flash using the Persist Tare function. Note that because
the Pitch and Roll axes are being tared, the procedure is dependent on the device’s orientation relative
to North so follow steps 3-5 carefully.
1. Power on the FSM300 and activate the Rotation Vector sensor.
2. Calibrate the magnetometer by rotating the device in a figure 8.
a. To validate that the magnetometer is well calibrated, you can look at the
Rotation Vector’s Accuracy Estimate field. This value provides an estimate for
how accurate the algorithm thinks it is in units of radians. A good goal is to
confirm that the Accuracy Estimate is <10 degrees (0.1745 radians). If
performing a Figure 8 motion does not reduce the accuracy estimate below 10
degrees than move to a cleaner magnetic environment.
3. Calibrate the accelerometer by positioning the device in 4-6 unique orientations and
ensuring the device is stable for a few seconds in each orientation.
a. One way to think about this is to imagine the device is a cube and set it down on
each face (upside down, right side, left side, on its front, its back).
4. Set the device down for a few seconds so that the gyroscope ZRO can calibrate as well.
5. Determine North in your current environment.
a. You can either look at a physical compass, or look at the Rotation Vector to
determine where North is. When the Rotation Vector reads W=1, X=0, Y=0, Z=0
the device is pointed North.
6. Position the device so that your desired forward direction is pointed North and make
sure the device is level.
7. Run the Tare Now command with the following settings:
Byte
Name
Value
Description

June 2017 Document 1000-4126 - FSM300 Tare Function Usage Guide - Revision 1.1
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0
Report ID
0xF2
Command
Request
1
Sequence Number
0x00
2
Command
0x03
Tare Command
3
P0 (Subcommand)
0x00
Tare Now
4
P1 (Bitmap of Axes)
0x07
All 3 axes (X,Y,Z)
5
P2 (Rotation Vector basis)
0x00
Rotation Vector
6-11
Reserved
0x00
Reserved
8. Run the Persist Tare command with the following settings:
Byte
Name
Value
Description
0
Report ID
0xF2
Command
Request
1
Sequence Number
0x00
2
Command
0x03
Tare Command
3
P0 (Subcommand)
0x01
Persist Tare
4-11
Reserved
0x00
Reserved
9. This will save the current settings into the Sensor Orientation FRS config record (See SH-
2 Reference Manual Section 4.3.4). Now these settings will be the default upon next
boot.
Set Current Forward Direction (User Tare)
In this example, the user is operating the device at their desk. They want to define the forward
orientation before starting a game, so all that needs to be done is tare the Z-axis (yaw): the other axes,
which define “level” do not need to be changed from their previously established configuration. This
could be done via an on-screen GUI or button on the device. Because only the Z-axis is being tared, the
user does not need to align the device to North.
1. Ideally the sensors would be calibrated well by the following steps:
a. Power on the FSM300 and activate the Rotation Vector sensor.
b. Calibrate the magnetometer by rotating the device in a figure 8.
c. Set the device down for a few seconds so that the gyroscope ZRO can calibrate
as well.
2. Position the device into your desired forward direction orientation.
3. Run the Tare Now command with the following settings:
Byte
Name
Value
Description
0
Report ID
0xF2
Command
Request
1
Sequence Number
0x00
2
Command
0x03
Tare Command
3
P0 (Subcommand)
0x00
Tare Now

June 2017 Document 1000-4126 - FSM300 Tare Function Usage Guide - Revision 1.1
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4
P1 (Bitmap of Axes)
0x04
Tare ONLY on Z-
axis
5
P2 (Rotation Vector basis)
0x00
Rotation Vector
6-11
Reserved
0x00
Reserved
4. After running this setting, the outputs of the Rotation Vector will be reoriented to this
new forward direction. This setting will revert to the Sensor Orientation FRS config
record (that was set via the last Persist Tare command) the next time the device is
rebooted.
How to Apply Tare Changes to Multiple Devices At Production
It is likely that when using the FSM300 on a production device, the orientation of the sensor will
be the same on many units. Rather than taring each individual unit, you can apply the Tare settings to
any number of additional units by using the FRS Sensor Orientation configuration record. General steps
for this are listed below. For further information about reading/writing FRS records contact Hillcrest
Labs.
1. Run the full Tare procedure listed above (labeled as First Time Setup) on a “reference” device.
2. Read the Sensor Orientation FRS record from the reference device.
3. Copy this FRS record to each device’s Sensor Orientation FRS record.
4. Now these devices will have identical Tare settings on the next hub reset.
References*
1. 1000-3625 SH-2 Reference Manual, Hillcrest Labs

June 2017 Document 1000-4126 - FSM300 Tare Function Usage Guide - Revision 1.1
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