Propeller Manual

JMP – Assembly Language Reference
JMP
Instruction: Jump to address.
JMP 〈#〉 Address
• Address (s-field) is the register or a 9-bit literal whose value is the address to jump to.
Opcode Table:
–INSTR– ZCRI –CON– –DEST– –SRC– Z Result C Result Result Clocks
010111 000i 1111 --------- sssssssss
Result = 0 --- Not Written 4
Concise Truth Table:
In Out
Destination
1
Source Z C Effects Destination
2
Z C
3
$----_----; - $----_----; - - -
wr wz wc
31:9 unchanged, 8:0 = PC+1 0 1
1
Destination is normally ignored for typical JMP usage, however if the WR effect is given, the JMP instruction becomes a JMPRET
instruction and Destination’s s-field (lowest 9 bits) are overwritten with the return address (PC+1).
2
Destination is not written unless the WR effect is given.
3
The C flag is set (1) unless PC+1 equals 0; very unlikely since it would require the JMP to be executed from the top of cog RAM
($1FF; special purpose register VSCL).
Explanation
JMP sets the Program Counter (PC) to Address causing execution to jump to that location in
Cog RAM.
JMP is closely related to the CALL, JMPRET, and RET commands; in fact, they are all
the same opcode but with different r-field and i-field values and varying assembler-driven
and user-driven d-field and s-field values.
Conditional Jumps
Conditional jumps, and conditional execution of any instruction, is achieved by preceding the
instruction with a condition in the form:
IF_x. See IF_x (Conditions) on page 295 for more
information.
The Here Symbol ‘
$’
The ‘Here’ Symbol,
$, represents the current address. During development and debugging,
the Here Symbol ‘
$’ is often used in the JMP instruction’s Address field (i.e., JMP #$) to
cause the cog to endlessly loop in place. It may also be used as a relative jump back or
forward a number of instructions, for example:
Page 298 · Propeller Manual v1.1