Determine fixed-point data type
H = NumericTypeScope
NumericTypeScope is an object that provides
information about the dynamic range of your data. The scope provides
a visual representation of the dynamic range of your data in the form
log2 histogram. In this histogram, the bit
weights appear along the X-axis, and the percentage of occurrences
along the Y-axis. Each bin of the histogram corresponds to a bit in
the binary word. For example, 20 corresponds
to the first integer bit in the binary word, 2-1 corresponds
to the first fractional bit in the binary word.
The scope suggests a data type in the form of a
that satisfies the specified criteria. See the section on Bit Allocation
in Dialog Panels.
H = NumericTypeScope
NumericTypeScope object that you can use to view
the dynamic range of data in MATLAB®. To view the
H, use the
brings it into view. Closing the scope window does not delete the
object from your workspace. If the scope object still exists in your
workspace, you can open it and bring it back into view using the
your data and allows you to visualize the dynamic range. The object
previously collected information about the variable between each call
system resources (such as memory, file handles or hardware connections)
and allows all properties and input characteristics to be changed.
all stored information from the
Resetting the object clears the information displayed in the scope
NumericTypeScope can also help you identify
any values that are outside range or below precision based on the
current data type. To prepare the
identify them, provide an input variable that is a
and verify that one of the following conditions is true:
DataTypeMode of the
is set to
Scaled doubles: binary point scaling.
of the Fixed-Point
fipref object is
When the information is available, the scope indicates values that are outside range, below precision, and in range of the data type by color-coding the histogram bars as follows:
Blue — Histogram bin contains values that are in range of the current data type.
Red — Histogram bin contains values that are outside range in the current data type.
Yellow — Histogram bin contains values that are below precision in the current data type.
For an example of the scope color coding, see the figures in Vertical Units.
See also Legend in Dialog Panels.
See the Examples section
to learn more about using the
select data types.
NumericTypeScope opens with the default
toolbars displayed at the top of the window and the dialog panels
to the right.
NumericTypeScope configuration allows
you to control the behavior and appearance of the scope window.
To open the Configuration dialog box, select File > Configuration > Edit, or, with the scope as your active window, press the N key.
The Configuration Dialog box contains a series of panes each containing a table of configuration options. See the reference section for each pane for instructions on setting the options on each one. This dialog box has one pane, the Core pane, with only one option, for General UI settings for the scope user interface.
To save configuration settings for future use, select File > Configuration > Save as. The configuration
settings you save become the default configuration settings for the
Before saving your own set of configuration settings in the matlab/toolbox/fixedpoint/fixedpoint folder, save a backup copy of the default configuration settings in another location. If you do not save a backup copy of the default configuration settings, you cannot restore these settings at a later time.
To save your configuration settings for future use, save them
in the matlab/toolbox/fixedpoint/fixedpoint folder with the file name
You can re-save your configuration settings at anytime, but remember
to do so in the specified folder using the specified file name.
The Core pane in the Configuration dialog box controls the general settings of the scope.
Click General UI and then click Options to open the Core:General UI Options dialog box.
Display the full source path in the title bar—Select this check box to display the file name and variable name in the scope title bar. If the scope is not from a file, or if you clear this check box, the scope displays only the variable name in the title bar.
Open message log—Control when the Message Log window opens. The Message log window helps you debug issues with the scope. Choose to open the Message Log window for any of these conditions:
for any new messages
for warn/fail messages
only for fail messages
The option defaults to
for warn/fail messages.
You can open the Message Log at any time by selecting Help > Message Log or by pressing Ctrl+M. The Message Log dialog box provides a system level record of loaded configuration settings and registered extensions. The Message Log displays summaries and details of each message, and you can filter the display of messages by Type and Category.
Type—Select the type of
messages to display in the Message Log. You can select
Fail. Type defaults to
Category—Select the category
of messages to display in the Message Log. You can select
Extension. The scope uses Configuration
messages to indicate when new configuration files are loaded, and
Extension messages to indicate when components are registered. Category
The scope Bit Allocation dialog panel, as shown in the following figure, offers you several options for specifying data type criteria.
You can use this panel to specify a known word length and the desired maximum occurrences outside range. You can also use the panel to specify the desired number of occurrences outside range and the smallest value to be represented by the suggested data type. For streaming data, the suggested numerictype object adjusts over time in order to continue to satisfy the specified criteria.
The scope also allows you to interact with the histogram plot. When you select Graphical control on the Bit Allocation dialog panel, you enable cursors on either side of the binary point. You can interact with these cursors and observe the effect of the suggested numerictype on the input data. For example, you can see the number of values that are outside range, below precision, or both. You can also view representable minimum and maximum values of the data type.
The scope Legend panel informs you which colors the scope uses to indicate values. These colors represent values that are outside range, in range, or below precision when displayed in the scope.
The Resulting Type panel describes the fixed-point data type as defined by scope settings. By manipulating the visual display (via the Bit Allocation panel or with the cursors) you can change the value of the data type.
The Data Details section displays the percentage of values that
fall outside range or below precision with the
located at the top of this panel. SQNR (Signal Quantization Noise
Ratio) varies depending on the signal. If the parameter has no value,
then there is not enough data to calculate the SQNR. When
scope information or the
numerictype changes, the
Type Details section provides details about the fixed-point data type.
The Input Data panel provides statistical information about
the values currently displayed in the
Use the Vertical Units selection to display values that are outside range or below precision as a percentage or as an actual count. For example, the following image shows the values that are outside range or below precision as a percentage of the total values.
This next example shows the values that are outside range or below precision as an actual count.
NumericScopeType GUI offers a View > Bring All NumericType
Scopes Forward menu option to help you
NumericTypeScope windows. Selecting
this option or pressing Ctrl+F brings all
into view. If a
NumericTypeScope window is not
currently open, this menu option opens the window and brings it into
Activate the Toolbar by selecting View > Toolbar. When this tool is active, you can dock or undock the scope from the GUI.
The toolbar feature is for the Mac only. Selecting Toolbar on Windows® and UNIX® versions displays only an empty toolbar. The docking icon always appears in the GUI in the upper-right corner for these versions.
Use this method to release system resources (such as memory, file handles or hardware connections) and allow all properties and input characteristics to be changed.
Use this method to clear the information stored in the object
Doing so allows you to reuse
H to process
data from a different variable.
Use this method to open the scope window and bring it into view.
Use this method to process your data and visualize the dynamic range in the scope window.
Set the fi object DataTypeOverride to Scaled Doubles, and then view its dynamic range.
fp = fipref; initialDTOSetting = fp.DataTypeOverride; fp.DataTypeOverride = 'ScaledDoubles'; a = fi(magic(10),1,8,2); b = fi([a; 2.^(-5:4)],1,8,3); h = NumericTypeScope; step(h,b); fp.DataTypeOverride = initialDTOSetting;
The log2 histogram display shows that the values appear both outside range and below precision in the variable. In this case, b has a data type of numerictype(1,8,3). The numerictype(1,8,3) data type provides 5 integer bits (including the signed bit), and 3 fractional bits. Thus, this data type can represent only values between -2^4 and 2^4- 2^-3 (from -16 to 15.8750). Given the range and precision of this data type, values greater than 2^4 fall outside the range and values less than 2^-3 fall below the precision of the data type. When you examine the NumericTypeScope display, you can see that values requiring bits 5, 6, and 7 are outside range and values requiring fractional bits 4 and 5 are below precision. Given this information, you can prevent values that are outside range and below precision by changing the data type of the variable b to numerictype(0,13,5).
View the dynamic range, and determine an appropriate numeric type for a fi object with a DataTypeMode of Scaled double: binary point scaling.
Create a numerictype object with a DataTypeMode of Scaled double: binary point scaling. You can then use that numerictype object to construct your fi objects. Because you set the DataTypeMode to Scaled double: binary point scaling, the NumericTypeScope can now identify overflows in your data.
T = numerictype; T.DataTypeMode = 'Scaled double: binary point scaling'; T.WordLength = 8; T.FractionLength = 6; a = fi(sin(0:100)*3.5, T); b = fi(cos(0:100)*1.75,T); acc = fi(0,T); h = NumericTypeScope; for i = 1:length(a) acc(:) = a(i)*0.7+b(i); step(h,acc) end
This dynamic range analysis shows that you can represent the entire range of data in the accumulator with 5 bits; two to the left of the binary point (integer bits) and three to the right of it (fractional bits). You can verify that this data type is able to represent all the values by changing the WordLength and FractionLength properties of the numerictype object T. Then, use T to redefine the accumulator.
To view the dynamic range analysis based on this new data type, reset the NumericTypeScope object h, and rerun the loop.
T.WordLength = 5; T.FractionLength = 2; acc = fi(0,T); release(h) reset(h) for i = 1:length(a) acc(:) = a(i)*0.7 + b(i); step(h,acc) end