Page 45 - Designing Autonomous Mobile Robots : Inside the Mindo f an Intellegent Machine

Chapter 3

Kernels and tasks

Real-time software concepts are almost as old as conventional programming con-
cepts. A software program that allows the machine resources to be divided between
multiple tasks is called a real-time kernel. The name kernel is appropriate because a
kernel is the small but critical center of the programming environment. It is basi-
cally a task switch.
A real-time operating system contains a kernel and the basic disk, keyboard, mouse,
and communications facilities found in conventional operating systems. Special
microcomputer systems designed for factory automation sported simple real-time
operating systems as early as the 1970s.

Serial Input Interrupt

Push Registers on Stack_0

Swap Stack Pointer to access
Stack_1

Get Serial Byte from
UART into Register A Get Character
Subroutine

Return from subroutine into
serial program Push Registers
onto Stack_1
text

Call Serial Task
Serial Task Exit
Exit
Swap Stack Pointer back to Pop Registers
Stack_0 from Stack_1

Return from
Pop Registers off of Stack_0
Subroutine w/
Character
Return from Interrupt

Main Program Thread Communications Thread

Figure 3.3. A simple multitasking serial input routine

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