Hardware-Implemented Single-Step for Microprogrammed Processor

Hardware-Implemented Single-Step for Microprogrammed Processor

       In a Tightly Coupled Multiprocessor environment, a
problem may be encountered on one of the processors in the system.
Because of this there exists the need to analyze one processor while
the rest are inactive.  In order to ensure instruction execution will
occur on one processor while the others are stopped, the other
processors must be at an instruction boundary.  This is necessary to
ensure no 'locks' are active between processors which would halt
operation.  This article describes the implementation of a scheme to
allow one processor to be analyzed while the others are inactive.
      Features are:
      -  allows single-processor analysis in a tightly
         coupled multiprocessor environment,
      -  instruction boundary stop function implemented
         entirely in hardware,
      -  less complex than a microcode solution to
         instruction single stepping,
      -  better performance than the microcode solution,
      -  not dependent on microcode debug before use

      This disclosure is implemented in hardware manual-ops. First,
all processors are stopped at the desired time. Clocks and microcode
are not controllable to a single processor.  When they are stopped
(started), they are stopped (started) on all processors at the same
time.

      The instruction stepping routine (which is a Hardware Manual
Op) starts by the Service Processor scanning in the correct values
into all processors in the system.  The processor to be analyzed (Px)
will have the 'Stop' latch scanned to the 'on' position.  (Refer to
the figure.)  This will halt operation by causing an infinite hold
off in that processor even when clocks and microcode...