Hardware reference guide

7535 Hardware Reference Guide 35
Chapter 3: The Software
System Structure
Memory Monitoring
When the free memory drops below a configurable limit, the shell sends a ‘hiber-
nate’ message to the last used application window. Application windows are sup-
posed to reduce their memory consumption when they receive this message. If the
free memory situation has not improved, the system monitor will send hibernate
messages to the other windows.
Power Monitoring
The power monitor provides two different means of feedback to the user.
The first method of feedback is a battery-gauge icon in the system tray. This icon,
which resembles a battery, shows the level of charge left in the main battery.
When the battery is fully charged the icon is completely green, when the battery is
completely discharged, the battery is red. The other levels in between vary in the
amount of green and red in the battery icon (for example, at 60% charge level the
battery is 3/5 green and 2/5 red). The shades of red and green will be chosen so that
they display as light and dark on a monochrome display.
The battery-gauge icon is replaced with a icon displaying a power connector when
the terminal is connected to external power and is not charging. It is replaced with
an icon displaying a battery with a lighting bolt when the terminal is connected to
external power and the battery is being charged.
The second method of feedback is the display of popup messages when the main
battery level drops below a certain limit or the battery life has been exceeded.
Security Monitoring
The system monitor thread is also responsible for the current security level on the
terminal.
The terminal has three security levels: User, Teklogix, and Supervisor. The system
monitor task monitors the security level and will display an icon in the system tray if
the terminal is in the Teklogix or Supervisor level. Any application that needs to set
or get the current security level should do it through a shell API that will be handled
by the system monitor task.