Each read or write access is for a single element only. For example, submatrix access and array copies are not supported.

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 supported.

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 this code, r1 does not map to RAM:

if (mod(i,2) > 0)
    a = r1(u);
else
    r1(i) = u;
end 

You can 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 r1 to RAM, rewrite the previous code as:

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, bigarray does not map to RAM because it does not depend on u:

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; 

The RAM size is greater than or equal to the RAMMappingThreshold value. The RAM size is the product of Array Size * Word Length * Complexity, where:

Access to the persistent variable that you are mapping to RAM is not in a loop, such as a for loop, unless the loop is unrolled. For more information, see coder.unroll.

Access to the persistent variable that you are mapping to RAM is not in a nested conditional statement, such as a nested if statement or nested switch statement.