In the HDL Workflow Advisor, select MATLAB to HDL Workflow > Code Generation > Optimizations tab.
Select the Map persistent array variables to RAMs option.
Set the RAM mapping threshold to
the size (in bits) of the smallest persistent array, user-defined System object™ private
dsp.Delay that you want to map to RAM.
The following table shows a summary of the RAM mapping behavior for persistent arrays and private properties of a user-defined System object.
|Map Persistent Array Variables to RAMs Setting||Mapping Behavior|
Map to RAM. For restrictions, see RAM Mapping Restrictions.
Map to registers in the generated HDL code.
When you enable RAM mapping, a persistent array or user-defined System object private property maps to a block RAM when all of the following conditions are true:
Each read or write access is for a single element only. For example, submatrix access and array copies are not allowed.
Address computation logic is not read-dependent. For example, computation of a read or write address using the data read from the array is not allowed.
Persistent variables or user-defined System object private properties are initialized to 0 if they have a cyclic dependency. For example, if you have two persistent variables, A and B, you have a cyclic dependency if A depends on B, and B depends on A.
If an access is within a conditional statement, the
conditional statement uses only simple
logic expressions (
or relational operators. For example, in the following code,
not map to RAM:
if (mod(i,2) > 0) a = r1(u); else r1(i) = u; end
Rewrite complex conditions, such as conditions that call functions,
by assigning them to temporary variables, and using the temporary
variables in the conditional statement. For example, to map
RAM, rewrite the previous code as follows:
temp = mod(i,2); if (temp > 0) a = r1(u); else r1(i) = u; end
The persistent array or user-defined System object private property value depends on external inputs.
For example, in the following code,
not map to RAM because it does not depend on
function z = foo(u) persistent cnt bigarray if isempty(cnt) cnt = fi(0,1,16,10,hdlfimath); bigarray = uint8(zeros(1024,1)); end z = u + cnt; idx = uint8(cnt); temp = bigarray(idx+1); cnt(:) = cnt + fi(1,1,16,0,hdlfimath) + temp; bigarray(idx+1) = idx;
RAMSize is greater
than or equal to the
RAMSize is the product
NumElements * WordLength * Complexity.
the number of elements in the array.
the number of bits that represent the data type of the array.
2 for arrays with a complex base type; 1 otherwise.
If any of the above conditions is false, the persistent array or user-defined System object private property maps to a register in the HDL code.
A summary of the mapping behavior for a
dsp.Delay System object is
in the following table.
|Map Persistent Array Variables to RAMs Option||Mapping Behavior|
If any of the conditions
are false, the