User`s guide

Architecture
5-24 AT85C51SND3Bx Firmware User’s Guide
7691A–MP3–08/07
5.3.1 The Scheduler The firmware system is driven by an endless scheduler which activates tasks, one at a
time, in a round robin manner. The scheduler loops on a static list. Refer to Section
6.2.12 for configuring the scheduler.
Note that each task executes “at will”, i.e. the duration of their execution is not limited.
Thus, in order to have the system running smoothly, each task should perform its duty
for the shortest amount of time.
5.3.2 The Tasks Task is a generic entity that provides well-defined services to the Customer MMI layer. It
integrates the on-chip peripherals and the software layer that controls them and pro-
vides high-level information.
Figure 5-3. Inner task logic representation.
The Atmel demo firmware implements 8 tasks:
– MMI manager task
– Power task
– USB task
– Player task
– Recorder task
– Viewer task
– Explorer task
– Update task
5.3.3 The Inter-Task
Communication
The bi-directional communication system between tasks is based on the management
of two kind of messages: “command” and “event”.
 “command” is a request that a task does a specific action. The “command”
messages can be mailed by tasks or MMI applications. They are destined to all
tasks except the MMI manager task.
Drivers
On-chip
peripherals
Processing
management
Communication
interface
On-board devices
Task
Round-robin scheduler
Public routines
Command/Event