Propeller Manual

WAITCNT – Assembly Language Reference
Page 368 · Propeller Manual v1.1
WAITCNT
Instruction: Pause a cog’s execution temporarily.
WAITCNT Target, 〈#〉 Delta
Result: Target + Delta is stored in Target.
•
Target (d-field) is the register with the target value to compare against the System
Counter (
CNT). When the System Counter has reached Target’s value, Delta is added
to Target and execution continues at the next instruction.
T
•
Delta (s-field) is the register or a 9-bit literal whose value is added to Target’s value in
preparation for the next
WAITCNT instruction. This creates a synchronized delay
window.
T
Opcode Table:
–INSTR– ZCRI –CON– –DEST– –SRC– Z Result C Result Result Clocks
111110 001i 1111 ddddddddd sssssssss
Result = 0 Unsigned Carry Written 5+
Concise Truth Table:
In Out
Destination Source Z C Effects Destination Z C
$0000_0000; 0 $0000_0000; 0 - -
wz wc
$0000_0000; 0 1 0
$FFFF_FFFF; 4,294,967,295 $0000_0001; 1 - -
wz wc
$0000_0000; 0 1 1
$0000_0000; 0 $0000_0001; 1 - -
wz wc
$0000_0001; 1 0 0
Explanation
WAITCNT, “Wait for System Counter,” is one of four wait instructions (T WAITCNT, WAITPEQ,
WAITPNE, and WAITVID) used to pause execution of a cog until a condition is met. The WAITCNT
instruction pauses the cog until the global System Counter equals the value in the Target
register, then it adds Delta to Target and execution continues at the next instruction. The
WAITCNTT instruction behaves similar to Spin’s WAITCNT command for Synchronized Delays;
see
T
WAITCNT on page . 218
If the
WZ effect is specified, the Z flag will be set (1) if the sum of Target and Delta is zero. If
the
WC effect is specified, the C flag will be set (1) if the sum of Target and Delta resulted in a
32-bit carry (overflow). The result will be written to Target unless the
NR effect is specified.