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Lock and Unlock

You can find the following topics on this page:

  • The sequences of synchronization protocol to handle lock/unlock transactions between processes.
  • The algorithm to handle synchronization protocol within interchiplet.
  • The algorithm to calculate the end cycle of one lock/unlock transaction.

Command syntax

# lock
LOCK <src_x> <src_y> <uid>
WRITE <cycle> <src_x> <src_y> <dst_x> <dst_y> <nbytes=1> <desc=0x40000>

# unlock
UNLOCK <src_x> <src_y> <uid>
WRITE <cycle> <src_x> <src_y> <dst_x> <dst_y> <nbytes=1> <desc=0x80000>

src_x and src_y present the source address of the process that locks or unlocks the mutex. uid specifies the unique ID of the mutex.

The cycle field in the WRITE command presents the time when the process locks or unlocks the mutex.

flowchart TB

subgraph lock
A1[__src_x]
A2[__src_y]
A3[__uid]
end

subgraph LOCK command
B1[src_x]
B2[src_y]
B3[dst_x]
B4[dst_y=0]
end

subgraph WRITE command
C0[cycle]
C1[src_x]
C2[src_y]
C3[dst_x]
C4[dst_y=0]
C6[nbytes=1]
C7[desc=0x80000]
end

A1 -.-> B1 -.-> C1
A2 -.-> B2 -.-> C2
A3 -.-> B3 -.-> C3

flowchart TB

subgraph unlock
D1[__src_x]
D2[__src_y]
D3[__uid]
end

subgraph UNLOCK command
E1[src_x]
E2[src_y]
E3[dst_x]
E4[dst_y=0]
end

subgraph READ command
F0[cycle]
F1[src_x]
F2[src_y]
F3[dst_x]
F4[dst_y=0]
F6[nbytes=1]
F7[desc=0x40000]
end

D1 -.-> E1 -.-> F1
D2 -.-> E2 -.-> F2
D3 -.-> E3 -.-> F3

Command Sequence

Handle LOCK and UNLOCK Command

The LOCK and UNLOCK commands are used to lock one specified mutex. When one mutex is locked by one process, other processes cannot lock the mutex until the mutex is released. uid specifies the unique ID of the mutex.

The rules to handle LOCK and UNLOCK commands are listed below:

  • When interchiplet receives one LOCK command,
    • If the specified mutex is locked, check the source of the LOCK command and the source that locked the specified mutex.
    • If the source of the LOCK command is the same as the source that locked the mutex, ignore the LOCK command. interchiplet returns one RESULT command without any result.
    • Otherwise, interchiplet registers the LOCK command.
    • Otherwise, interchiplet locks the mutex and returns one RESULT command without any result.
  • When interchiplet receives one UNLOCK command,
    • If the specified mutex is locked, interchiplet unlocks the mutex and returns one RESULT command without any result.
      • If there are pending LOCK commands, select the first LOCK pending command to lock the mutex. interchiplet returns one RESULT command without any result to the selected LOCK command.
    • Otherwise, ignore the UNLOCK command. interchiplet returns one RESULT command without any result.

One example of the LOCK and UNLOCK commands is shown below.

sequenceDiagram
autonumber

participant SP0 as Simulator<br/>Process 0
participant interchiplet
participant SP1 as Simulator<br/>Process 1

activate SP0
activate SP1

Note over SP0,SP1: Example starts

SP1->>interchiplet: LOCK 0 1 255
deactivate SP1
activate interchiplet

Note over interchiplet: Lock the mutex.

interchiplet->>SP1: RESULT 0
deactivate interchiplet
activate SP1

SP0->>interchiplet: LOCK 0 0 255
deactivate SP0
activate interchiplet

Note over interchiplet: Register LOCK command.

deactivate interchiplet

SP1->>interchiplet: UNLOCK 0 1 255
deactivate SP1
activate interchiplet

Note over interchiplet: Unlock the mutex.

interchiplet->>SP1: RESULT 0
activate SP1

Note over interchiplet: Lock the mutex by one pending LOCK command.

interchiplet->>SP0: RESULT 0
deactivate interchiplet
activate SP0

SP0->>interchiplet: UNLOCK 0 0 255
deactivate SP0
activate interchiplet

Note over interchiplet: Unlock the mutex.

interchiplet->>SP0: RESULT 0
deactivate interchiplet
activate SP0

SP0->>interchiplet: LOCK 0 0 255
deactivate SP0
activate interchiplet

Note over interchiplet: Lock the mutex.

interchiplet->>SP0: RESULT 0
activate SP0
deactivate interchiplet

SP0->>interchiplet: UNLOCK 0 0 255
deactivate SP0
activate interchiplet

Note over interchiplet: Unlock the mutex.

interchiplet->>SP0: RESULT 0
activate SP0
deactivate interchiplet

Note over SP0,SP1: Example ends

deactivate SP0
deactivate SP1

Simulator Process 0 and Simulator Process 1 require the mutex 255. Simulator Process 1 locks the mutex first when interchiplet receives the LOCK command (1). Then, Simulator Process 0 requires the mutex by the LOCK command (3). Simulator Process 0 blocks until Simulator Process 1 releases the mutex by the UNLOCK command (4). Then, Simulator Process 0 blocks the mutex 255 twice.

With valid timing information, the order to lock the mutex is specified by the timing information, as bold sentences below.

  • When interchiplet receives one LOCK command,
    • If the specified mutex is locked, check the source of the LOCK command and the source that locked the specified mutex.
      • If the source of the LOCK command is the same as the source that locked the mutex, ignore the LOCK command. interchiplet returns one RESULT command without any result.
      • Otherwise, interchiplet registers the LOCK command.
    • Otherwise, check the source of the LOCK command with the order specified by timing information.
      • If the source of the LOCK command matches the order specified by timing information, interchiplet locks the mutex and returns one RESULT command without any result.
      • Otherwise, interchiplet registers the LOCK command.
  • When interchiplet receives one UNLOCK command,
    • If the specified mutex is locked, interchiplet unlocks the mutex and returns one RESULT command without any result.
      • If there are pending LOCK commands, check whether the next source that lock the mutex exists in the pending LOCK commands, according to the timing information.
        • If the command exists, select the matched LOCK pending command to lock the mutex. interchiplet returns one RESULT command without any result to the selected LOCK command.
        • Otherwise, do nothing.
    • Otherwise, ignore the UNLOCK command. interchiplet returns one RESULT command without any result.

As shown in the figure below, Simulator Process 0 locks the mutex first. Then Simulator Process 1 locks the mutex after Simulator Process 0 unlocks the mutex. At last, Simulator Process 0 locks the mutex again.

sequenceDiagram
autonumber

participant SP0 as Simulator<br/>Process 0
participant interchiplet
participant SP1 as Simulator<br/>Process 1

activate SP0
activate SP1

Note over SP0,SP1: Example starts

SP1->>interchiplet: LOCK 0 1 255
deactivate SP1
activate interchiplet

Note over interchiplet: Register LOCK command because order mismatches.

deactivate interchiplet

SP0->>interchiplet: LOCK 0 0 255
deactivate SP0
activate interchiplet

Note over interchiplet: Lock the mutex.

interchiplet->>SP0: RESULT 0
deactivate interchiplet
activate SP0

SP0->>interchiplet: UNLOCK 0 0 255
deactivate SP0
activate interchiplet

Note over interchiplet: Unlock the mutex.

interchiplet->>SP0: RESULT 0
activate SP0

Note over interchiplet: Lock the mutex by one pending LOCK command<br>matching the order.

interchiplet->>SP1: RESULT 0
deactivate interchiplet
activate SP1

SP0->>interchiplet: LOCK 0 0 255
deactivate SP0
activate interchiplet

Note over interchiplet: Register LOCK command.

deactivate interchiplet

SP1->>interchiplet: UNLOCK 0 1 255
deactivate SP1
activate interchiplet

Note over interchiplet: Unlock the mutex.

interchiplet->>SP1: RESULT 0
activate SP1

Note over interchiplet: Lock the mutex by one pending LOCK command<br>matching the order.

interchiplet->>SP0: RESULT 0
activate SP0
deactivate interchiplet

SP0->>interchiplet: UNLOCK 0 0 255
deactivate SP0
activate interchiplet

Note over interchiplet: Unlock the mutex.

interchiplet->>SP0: RESULT 0
activate SP0
deactivate interchiplet

Note over SP0,SP1: Example ends

deactivate SP0
deactivate SP1

Handle WRITE Command with the Lock and Unlock Flag

Similar to barrier transactions, when a process requires/releases one mutex, the process sends one request to a controller, like a mailbox. The location of the controller is configured in Popnet.

The cycle field in the WRITE command with the lock/unlock flag presents the time when the source component sends the lock/unlock requirement to the destination, referenced as src_cycle. WRITE commands with the lock/unlock flag do not need to pair with READ commands.

The SYNC command after one WRITE command with the lock/unlock flag means the source has received the acknowledgment. The task or flow in the source can continue after receiving the SYNC command. The execution cycle of the source should be adjusted to the value specified in the cycle field of SYNC commands.

Latency information provides four latency values (lat_0, lat_1, lat_2, and lat_3) for one lock/unlock transaction as one barrier transaction.

The request package is injected at src_cycle. Hence, the request package arrives at the controller at src_cycle + lat_1. If the mutex is not locked by src_cycle + lat_1, the controller sends the acknowledgment to the source. dst_cycle presents the cycle when the mutex is released.

The timing sequence of lock and unlock transactions is similar to the timing sequence of launch transactions. In summary,

  • The cycle of the SYNC command to the WRITE command is max(src_cycle + lat_1, dst_cycle) + lat_3.
  • The cycle of the SYNC command to the READ command is max(src_cycle + lat_1, dst_cycle) + lat_2.