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 4.4.6.2. PSL Procedure for Time-Sliced and 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 resume_element MMIO command is received by the first PSL, the PSL performs any operations necessary and sends the resume_element command to the next PSL. 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.

  1. When operating in an AFU-directed programming model, the PSL notifies the AFU of the process element being resumed. The AFU performs any necessary operations to resume execution of the process and then acknowledges the resumed process element. When the acknowledgment is received, the PSL continues with the next substep. The AFU is not notified of the added process element for all other programming models.

  2. The PSL writes an resume_element command to the psl_chained_command doubleword for the next PSL.

    • Write the value (x'00040000' || next_psl_id || link_of_element_to_resume) to the psl_chained_command.

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

When the resume_element command is detected by the next PSL, the PSL performs any operations necessary and sends the resume_element command to the next PSL. The resume_element command is detected by monitoring the psl_chained_command doubleword. 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.

  1. When operating in an AFU-directed programming model, the PSL notifies the AFU of the process element being resumed. The AFU performs any necessary operations to resume execution of the process and then acknowledges the resumed process element. When the acknowledgment is received, the PSL continues with the next substep. The AFU is not notified of the resumed process element for any other programming models.

  2. The PSL writes an resume_element command to the psl_chained_command doubleword for the next PSL.

    • Write the value (x'00040000' || next_psl_id || link_of_element_to_resume) to the psl_chained_command.

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

When the resume_element MMIO command is received or the resume_element command is detected by the last PSL, the PSL performs any operations necessary and sets the completion status in the software command/status word. The resume_element command is detected by monitoring the psl_chained_command doubleword. 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.

  1. When operating in an AFU-directed programming model, the PSL notifies the AFU of the process element being resumed. The AFU performs any necessary operations to resume execution of the process and then acknowledges the resumed process element. When the acknowledgment is received, the PSL continues with the next substep. The AFU is not notified of the resumed process element for any other programming models.

  2. The PSL sets the completion status in the software command/status field to indicate that the process has been successfully resumed.

    • The status field in sw_command_status is set to x'0004' 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'00040004' || first_psl_id || link_of_element_to_resume).


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