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 | 8..23 |
Concise Truth Table:
In | Out | ||||||
Destination | Source1 | Z | C | Effects | Destination2, 3 | Z | C |
$0000_0005; 5 | %0_00000111; 7 | - | - | wr wz wc | $0000_0005; 5 | 0 | 14 |
$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 | 14 |
$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, 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.
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 8 to 23 clock cycles to execute depending on the relation between the cog's hub access window and the instruction's moment of execution. See Hub for more information.
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