CD Shell Development: Command Services

Command Services

Command Services List

Modules are able to present a list of command services to the core. The list is a linear array made up of individual command service definitions, each of which define a single command supported by the module. These commands can then be invoked by a user by typing the name of the command in a script file or on the command line.

The definitions in the command services list must be in alphabetical order by command name. A 2-byte (16-bit) zero value terminates the list.

Command Service Definition

Offset	Size	Description
0	2 bytes	service routine pointer
2	2 bytes	flags
4	2 bytes	name pointer
6	2 bytes	description text pointer
8	2 bytes	help text pointer

Service Routine Pointer

This is the offset into the module segment of the handler routine that processes this command.

Flags

This field is a set of flags that determine how the command is handled. The bitfields are defined as follows:

Bit	Field	Description
[0]	Ignore	pretend this command is not in the list
[1]	Hide	don't display info about this command
[2]	Console	command available for use on the console
[3]	Script	command available for use in scripts
[15:4]	Reserved	these flags are reserved for future use

Name Pointer

This is the offset into the module segment of the command name, a null-terminated string.

Description Text Pointer

This is the offset into the module segment of the command description, a short string presented to the user in the master command list. If no description is provided, this field should be zeroed out.

Help Text Pointer

This is the offset into the module segment of the command help text, a small paragraph presented to the user when command-specific help is requested. If no help is provided, this field should be zeroed out.

Service Routine Environment

Call Context

The command service routine is called by the core with the following context:

Register	Contents
al	command source (Command.Console or Command.Script)
si	offset of command line tail (located in core segment)
cs	module segment
ds	module segment
es	module segment
gs	Core Services Table segment
ss:sp	global stack, far return pointer on top

Note: Command.Console and Command.Script are defined in cdshell.inc.

Return Context

The core expects the following context upon return from the service routine:

Register	Contents
ss:sp	global stack, far return pointer popped

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