The Assembler issued an error about a branch label being "defined differently in each pass." Prior to the label definition, a symbol was used that was defined to another symbol using .set; the latter symbol was defined with a .set to a constant value in a different file. In the PRU Assembly Language User's Guide, it specifies in 5.12 Directive Reference, under ".asg": The .asg directive can be used in many of the same ways as the .set directive, but while .set assigns a constant value (which cannot be redefined) to a symbol, .asg assigns a character string (which can be redefined) to a substitution symbol. The problem is eliminated when the symbol is defined to the other symbol using .asg. This is because .asg works like a macro replacement, which is what the user intended, while .set is for assigning a constant value to a symbol.