Propeller Manual

CNT – Assembly Language Reference
Page 282 · Propeller Manual v1.1
CNT
Register: System Counter register.
DAT
〈Label〉 〈Condition〉 Instruction DestOperand, CNT 〈Effects〉
•
Label is an optional statement label. See Common Syntax Elements, page 250.
•
Condition is an optional execution condition. See Common Syntax Elements, page 250.
•
Instruction is the desired assembly instruction. CNT is a read-only register and thus
should only be used in the instruction’s source operand.
•
DestOperand is a constant expression indicating the register that is operated on, and
optionally written to, using the value of
CNT in the instruction’s source operand. T
Explanation
The
CNT register contains the current value in the global 32-bit System Counter. The System
Counter serves as the central time reference for all cogs; it increments its 32-bit value once
every System Clock cycle.
CNT is a read-only pseudo-register; when used as an instruction’s source operand, it reads the
current value of the System Counter. Do not use
CNT as the destination operand; that only
results in reading and modifying the shadow register whose address
CNT occupies.
CNT is often used to determine an initial target value for a WAITCNT-based delay. The
following code performs an operation in a loop every ¼ second. See Registers, page 338, and
the Spin language
CNT section, page 73, for more information.
DAT
org 0 'Reset assembly pointer
AsmCode rdlong Delay, #0 'Get clock frequency
shr Delay, #2 'Divide by 4
mov Time, cnt 'Get current time
add Time, Delay 'Adjust by 1/4 second
Loop waitcnt Time, Delay 'Wait for 1/4 second
'<more code here> 'Perform operation
jmp #Loop 'loop back
Delay res 1
Time res 1