Performance Improvement via Early Interrupts

Performance Improvement via Early Interrupts

      Disclosed is a technique which improves the transmission media
utilization by incorporating two adapter hardware/microcode
interrupts.  This allows overlap of the network control program and
microcode work times with the hardware data transmission.  This
technique is illustrated in Fig. 2.

      Communication adapters, with Direct Memory Access (DMA)
capability, controlled by the IBM Network Control Program (NCP),
receive commands from the NCP as shown in Fig. 1.  The NCP prepares a
transmit buffer (1) and issues the transmit command to the adapter
microcode (2) to start the transmission.  The adapter then DMAs the
data (3) into its internal buffers, and (4) transmits the data onto
the transmission media.  The NCP is unaware of the transmission
progress until the hardware interrupts the adapter microcode (5), and
the microcode in turn interrupts the NCP (6).  At this time, the NCP
checks the status of the operation, and assuming NCP has another
transmit command for the adapter, the process is repeated.  The
transmission media is utilized only during the transmission times
(7).  During the NCP/microcode work times (8), the transmission media
is idle.  If time (8) is large compared to time (7), the media is not
highly utilized.

      With this invention, the first control program command (9) is
issued to the adapter microcode, which processes it, and (10) sends a
transmit request to the adapter hardware...