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 4.4.5.3. PSL Procedure for AFU-Directed Programming Models

Each PSL assigned to service the scheduled processes is configured with a unique identifier and the identifier of the next PSL in the list of PSLs servicing the processes. In addition, each PSL is identified as either the first PSL, the last PSL, both first and last PSL (only one PSL servicing the queue), or neither first or last PSL. The PSL ID Register contains the PSL unique identifier and the settings for first and last.

  Operations Performed by the First PSL (PSL_ID[L,F] = '01')

When the suspend_element MMIO command is received by the first PSL, the PSL checks to see if the process element being suspended is currently running. It performs any operations necessary, and sends the suspend_element command to the next PSL or sets the completion status in the software command/status word.

  1. The PSL notifies the AFU of the suspended process element. The AFU performs any necessary operations to suspend the process and then acknowledges the suspension of the process element. When the acknowledgment is received, the PSL continues with the next substep.

  2. If the process is running, the process is suspended. The PSL sets the completion status in the software command/status field to indicate that the process has been successfully suspended. The PSL is allowed to complete any outstanding transactions but should not start any new transactions for the process.

    • The status field in sw_command_status is set to x'0003' using a caching-inhibited DMA or special memory-update operation that is guaranteed not to corrupt memory if the operation fails. The final value of sw_command_status should be (x'00030003' || first_psl_id || link_of_element_to_suspend).

  3. If the process element is not running, the PSL writes a suspend command to the psl_chained_command doubleword for the next PSL.

    • Write the value (x'00030000' || next_psl_id || link_of_element_to_suspend) to the psl_chained_command.

    • The PSL does not start any process with a software state of complete, suspend, or terminate. A process element with the suspend flag set can be added to the PSL queue.

 Operations Performed by the Next PSL (PSL_ID[L,F] = '00')

When the suspend_element command is detected by the next PSL, the PSL checks to see if the process element being terminated is currently running. It performs any operations necessary, and sends the terminate_element command to the next PSL or sets the completion status in the software command/status word. The suspend_element command is detected by monitoring the psl_chained_command doubleword.

  1. The PSL notifies the AFU of the suspended process element. The AFU performs any necessary operations to suspend the process and then acknowledges the suspension of the process element. When the acknowledgment is received, the PSL continues with the next substep.

  2. If the process element is running, the process is suspended. The PSL is allowed to complete any outstanding transactions but should not start any new transactions for the process.

  3. The PSL writes a suspend command to the psl_chained_command doubleword for the next PSL.

    • Write the value (x'00030000' || next_psl_id || link_of_element_to_suspend) to the psl_chained_command.

    • The PSL does not start any process with a software state of complete, suspend, or terminate. A process element with the suspend flag set can be added to the PSL queue.

  Operations Performed by the Last PSL (PSL_ID[L] = '1')

When the suspend_element MMIO command is received or the suspend_element command is detected by the last PSL, the PSL checks to see if the process element being terminated is currently running. It performs any operations necessary, and sets the completion status in the software command/status word. The suspend_element command is detected by monitoring the psl_chained_command doubleword.

  1. The PSL notifies the AFU of the suspended process element. The AFU performs any necessary operations to suspend the process and then acknowledges the suspension of the process element. When the acknowledgment is received, the PSL continues with the next substep.

  2. If the process element is running, the process is suspended. The PSL is allowed to complete any outstanding transactions but should not start any new transactions for the process.

  3. The PSL sets the completion status in the software command/status field to indicate the process has been successfully suspended.

    • The status field in sw_command_status is set to x'0003' using a caching-inhibited DMA or special memory-update operation that is guaranteed not to corrupt memory if the operation fails. The final value of sw_command_status should be (x'00030003' || first_psl_id || link_of_element_to_suspend).

    • The PSL does not start any process with a software state of complete, suspend, or terminate. A process element with the suspend flag set can be added to the PSL queue.


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