Propeller Manual

3: Assembly Language Reference – LOCKCLR
Propeller Manual v1.1 · Page 303
LOCKCLR
Instruction: Clear lock to false and get its previous state.
LOCKCLR ID
Result: Optionally, previous state of lock is written to C flag.
• ID (d-field) is the register containing the ID (0 – 7) of the lock to clear.
Opcode Table:
–INSTR– ZCRI –CON– –DEST– –SRC– Z Result C Result Result Clocks
000011 0001 1111 ddddddddd ------111
ID = 0 Prior Lock State Not Written 7..22
Concise Truth Table:
In Out
Destination Source
1
Z C Effects Destination
2, 3
Z C
$0000_0005; 5 %0_00000111; 7 - -
wr wz wc
$0000_0005; 5 0
1
4
$0000_0005; 5 %0_00000111; 7 - -
wr wz wc
$0000_0005; 5 0 0
$0000_0000; 0 %0_00000111; 7 - -
wr wz wc
$0000_0000; 0 1
1
4
$0000_0000; 0 %0_00000111; 7 - -
wr wz wc
$0000_0000; 0 1 0
$0000_0008; 8
5
%0_00000111; 7 - -
wr wz wc
$0000_0000; 0 1 0
1
Source is automatically set to immediate value 7 by the assembler to indicate that this is the LOCKCLR hub instruction.
2
Destination is not written unless the WR effect is given.
3
Destination Out (written Destination) indicates the ID of the lock bit that was cleared.
4
The C flag indicates the previous state of the lock bit; in these cases the lock bit was previously set by a formerly executed LOCKSET
instruction (not shown). The next example clears the C flag because the lock bit was just cleared by the previous example.
5
Only the lowest 3 bits of Destination In are utilized, so a value of 8 is seen as lock bit ID 0.
Explanation
LOCKCLR is one of four lock instructions (LOCKNEW, LOCKRET, T LOCKSET, and LOCKCLR) used to
manage resources that are user-defined and deemed mutually exclusive.
LOCKCLR clears the
lock described by the register ID to zero (0) and returns the previous state of that lock in the
C flag; if the
WC effect is specified. The LOCKCLR instruction behaves similar to Spin’s LOCKCLR
command; see
LOCKCLR on page 120.
If the
WZ effect is specified, the Z flag is set (1) if the ID of the cleared lock is zero (0). If the
WC effect is specified, the C flag is set equal to the previous state of the lock. If the WR effect
is specified, the ID of the cleared lock is written to ID.
LOCKCLR is a hub instruction. Hub instructions require 7 to 22 clock cycles to execute
depending on the relation between the cog’s hub access window and the instruction’s moment
of execution. See Hub on page 24 for more information.