GE D20 Technical Overview page 50

D20/D200 Technical Overview
Real-Time Executive
The operating system of the peripheral units is a real-time executive, which controls process
scheduling, and resource and interrupt management. The real-time executive controls three basic
processes: watchdog, diagnostics and maintenance facility. It also controls some application
processes downloaded from the D20/D200.
The real-time executive supports pausing, time-outs and suspension of the maintenance process
while maintenance port operations are in progress. A limited number of monitor (debugging)
functions are available as development tools for creating new code for peripherals.
Watchdog and Reset Code
The 68HC11 microcomputer chip on the peripherals includes a built-in watchdog to help protect
against software failures. The reset code also performs the initialization in the peripherals.
Diagnostics
The diagnostic processes, governed by the real-time executive, include a sub-routine that
performs checks specific to the peripheral type.
Device Drivers
Peripheral modules have two device drivers:
• Serial Port, a serial communications interface which allows the connection of a VT100
terminal or PC for running maintenance facilities.
• HDLC drives the HDLC protocol controller for the D.20 Link between the D20 main
processor and I/O peripherals.
Peripheral Communications
The resident peripheral communication process functions continuously, requesting and receiving
data from the I/O peripherals, then forwarding these over the HDLC link to the D20 main
processor. Module-specific applications and configurations are downloaded to the D20 I/O
peripherals as required. Communication failures between the D20 main processor and D20 I/O
peripherals are logged and reported to the master if required.
Common Code Interface
The Common Code Interface provides quick and easy access to various programs making up the
peripheral common code. This interface reduces the size of the application code that is
downloaded from the D20/D200 by using a jump-table at a fixed address in the peripheral
module. The jump-table accesses the peripheral module library resources, executive entry points,
display functions and keyboard input/output for the maintenance port.
Promaint
Similar to WESMAINT on the D20 main processor, Promaint is the maintenance facility for the
peripheral modules. Promaint combines maintenance and monitor functions. The maintenance
portion is used to view data, or to verify that the module is functioning correctly by, for example,
forcing a control point and then checking to see whether the control operation took effect.
The monitor facility is designed to interpret commands from the maintenance port, such as
storing data to memory. It can also execute various application-dependent commands once an
application program has been downloaded from the D20/D200.
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