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5

Host interface and AServer

The host interface is provided by the AServer. This can be used simply as an application loader and

host file server, invoked by the irun command. The INQUEST tools have their own commands which

in turn load irun in order to load the application. The AServer may also be used to customize the

host interface if required.

5.1

The application loader – irun

irun

performs three functions, namely:

1

to initialize the target hardware;

2

to load a bootable application program onto the target hardware via the hardware serial link;

3

to serve the application, i.e. to respond to requests from the application program for access

to host services, such as host files and terminal input and output.

These steps are normally performed when irun is invoked.

5.2

AServer

The AServer (Asynchronous Server) system is a high performance interface system which allows

multiple processes on a target device to communicate via a hardware serial link with multiple

processes on some external device. The AServer software acts as a standard interface which is

independent of the hardware used. A simple example is shown in Figure 13, in which the external

device is the host.

irun

Services

Target

Host

gateway

gateway

Clients

Link

Target hardware

Figure 13

A simple software host-target interface

The AServer is a collection of programs, interface libraries and protocols that together create a

system to enable applications running on target hardware to access external services in a way that

is consistent, extensible and open. The software elements provided are:

a target gateway which runs on the target;

an irun gateway which runs on the host;

an iserver service which runs on the host;

an iserver converter which runs on the target;

a library of interface routines for use by client and service processes;

simple example services.