The Assembler incorporates constant expressions. Expressions can consist of operands, operators and functions. All expressions are 64 bits internally.
Operands
The following operands can be used:
User defined labels which are given the value of the location counter at the place they appear.
User defined variables defined by the SET directive
User defined constants defined by the EQU directive
Integer constants: constants can be given in several formats, including
Decimal (default): 10, 255
Hexadecimal (two notations): 0x0a, $0a, 0xff, $ff
Binary: 0b00001010, 0b11111111
Octal (leading zero): 010, 077
PC - the current value of the Program memory location counter
Floating point constants
Operators
The Assembler supports a number of operators which are described here. The higher the precedence, the higher the priority. Expressions may be enclosed in parentheses, and such expressions are always evaluated before combined with anything outside the parentheses. The associativity of binary operators indicates the evaluation order of chained operators, left associativity meaning they are evaluated left to right, i.e., 2 - 3 - 4 is (2 - 3) - 4, while right associativity would mean 2-3-4 is 2 - (3 - 4). Some operators are not assoiciative, meaning chaining has no meaning.
The following operators are defined:
Logical Not
Symbol: !
Description: Unary operator which returns 1 if the expression was zero, and returns 0 if the expression was nonzero Precedence: 12
Associativity: None
Example: ldi r16,!0xf0 ; Load r16 with 0x00
Bitwise Not
Symbol: ~
Description: Unary operator which returns the input expression with all bits inverted
Precedence: 12
Associativity: None
Example: ldi r16,~0xf0 ; Load r16 with 0x0f
Unary Minus
Symbol: -
Description: Unary operator which returns the arithmetic negation of an expression
Precedence: 14
Associativity: None
Example: ldi r16,-2 ; Load -2(0xfe) in r16
Multiplication
Symbol: *
Description: Binary operator which returns the product of two expressions
Precedence: 13
Associativity: Left
Example: ldi r30,label*2 ; Load r30 with label*2
Division
Symbol: /
Description: Binary operator which returns the integer quotient of the left expression divided by the right expression
Precedence: 13
Associativity: Left
Example: ldi r30,label/2 ; Load r30 with label/2
Modulo
Symbol: %
Description: Binary operator which returns the integer remainder of the left expression divided by the right expression
Precedence: 13
Associativity: Left
Example: ldi r30,label%2 ; Load r30 with label%2
Addition
Symbol: +
Description: Binary operator which returns the sum of two expressions
Precedence: 12
Associativity: Left
Example: ldi r30,c1+c2 ; Load r30 with c1+c2
Subtraction
Symbol: -
Description: Binary operator which returns the left expression minus the right expression
Precedence: 12
Associativity: Left
Example: ldi r17,c1-c2 ;Load r17 with c1-c2
Shift left
Symbol: <<
Description: Binary operator which returns the left expression shifted left the number given by the right expression
Precedence: 11
Associativity: Left
Example: ldi r17,1<<bitmask ;Load r17 with 1 shifted left bitmask times
Shift right
Symbol: >>
Description: Binary operator which returns the left expression shifted right the number given by the right expression
Precedence: 11
Associativity: Left
Example: ldi r17,c1>>c2 ;Load r17 with c1 shifted right c2 times
Less than
Symbol: <
Description: Binary operator which returns 1 if the signed expression to the left is Less than the signed expression to the right, 0 otherwise
Precedence: 10
Associativity: None
Example: ori r18,bitmask*(c1<c2)+1 ;Or r18 with an expression
Less or equal
Symbol: <=
Description: Binary operator which returns 1 if the signed expression to the left is Less than or Equal to the signed expression to the right, 0 otherwise
Precedence: 10
Associativity: None
Example: ori r18,bitmask*(c1<=c2)+1 ;Or r18 with an expression
Greater than
Symbol: >
Description: Binary operator which returns 1 if the signed expression to the left is Greater than the signed expression to the right, 0 otherwise
Precedence: 10
Associativity: None
Example: ori r18,bitmask*(c1>c2)+1 ;Or r18 with an expression
Greater or equal
Symbol: >=
Description: Binary operator which returns 1 if the signed expression to the left is Greater than or Equal to the signed expression to the right, 0 otherwise
Precedence: 10
Associativity: None
Example: ori r18,bitmask*(c1>=c2)+1 ;Or r18 with an expression
Equal
Symbol: ==
Description: Binary operator which returns 1 if the signed expression to the left is Equal to the signed expression to the right, 0 otherwise
Precedence: 9
Associativity: None
Example: andi r19,bitmask*(c1==c2)+1 ;And r19 with an expression
Not equal
Symbol: !=
Description: Binary operator which returns 1 if the signed expression to the left is Not Equal to the signed expression to the right, 0 otherwise
Precedence: 9
Associativity: None
Example: .SET flag=(c1!=c2) ;Set flag to 1 or 0
Bitwise And
Symbol: &
Description: Binary operator which returns the bitwise And between two expressions
Precedence: 8
Associativity: Left
Example: ldi r18,High(c1&c2) ;Load r18 with an expression
Bitwise Xor
Symbol: ^
Description: Binary operator which returns the bitwise Exclusive Or between two expressions
Precedence: 7
Associativity: Left
Example: ldi r18,Low(c1^c2) ;Load r18 with an expression
Bitwise Or
Symbol: |
Description: Binary operator which returns the bitwise Or between two expressions
Precedence: 6
Associativity: Left
Example: ldi r18,Low(c1|c2) ;Load r18 with an expression
Logical And
Symbol: &&
Description: Binary operator which returns 1 if the expressions are both nonzero, 0 otherwise
Precedence: 5
Associativity: Left
Example: ldi r18,Low(c1&&c2) ;Load r18 with an expression
Logical Or
Symbol: ||
Description: Binary operator which returns 1 if one or both of the expressions are nonzero, 0 otherwise
Precedence: 4
Associativity: Left
Example: ldi r18,Low(c1||c2) ;Load r18 with an expression
Conditional operator
Symbol: ? :
Syntax: condtion? expression1 : expression2
Description: Ternary operator which returns expression1 if condition is true, expression2 otherwise.
Precedence: 3
Associativity: None
Example:
ldi r18, a > b? a : b ; Load r18 with the maximum numeric value of a and b. Note: This feature was introduced in AVRASM 2.1 and is not available in 2.0 or earlier versions.
Functions
LOW(expression) returns the low byte of an expression
HIGH(expression) returns the second byte of an expression
BYTE2(expression) is the same function as HIGH
BYTE3(expression) returns the third byte of an expression
BYTE4(expression) returns the fourth byte of an expression
LWRD(expression) returns bits 0-15 of an expression
HWRD(expression) returns bits 16-31 of an expression
PAGE(expression) returns bits 16-21 of an expression
EXP2(expression) returns 2 to the power of expression
LOG2(expression) returns the integer part of log2(expression)
INT(expression) Truncates a floating point expression to integer (ie discards fractional part)
FRAC(expression) Extracts fractional part of a floating point expression (ie discards integer part).
Q7(expression) Converts a fractional floating point expression to a form suitable for the FMUL/FMULS/FMULSU instructions. (sign + 7-bit fraction)
Q15(expression) Converts a fractional floating point expression to a form suitable for the FMUL/FMULS/FMULSU instructions. (sign +15-bit fraction)
ABS() Returns the absolute value of a constant expression.
DEFINED(symbol) Returns true if symbolis previously defined using .equ/.set/.def directives. Normally used in conjunction with .if directives (.if defined(foo)), but may be used in any context. It differs from other functions in that parentheses around its argument are not required, and that it only makes sense to use a single symbol as argument.
STRLEN(string) returns the length of a string c+onstant, in bytes.