Computer Solutions Ltd

After supplying all your Embedded Development Tool needs for 42 years
Computer Solutions Ltd and its web shop are now closed.

Having reached the grand old age of 75 it is time to relax and fulfil other ambitions.

Its been an exciting ride with you, our customers, often on the bleeding edge of technology
and I thank you for your friendship, your trust, and your orders.

Stay well I wish you all success in your future projects.

Chris Stephens.

But what to do with the web site ? It has taken >12 man years of work to create a repository of knowledge on many aspects of the art and science of embedded microprocessor development and even after closing the shop it still gets over 4,000 visitors per month. So as a service to my customers I have decide to keep it live providing my technical insights on the products and then redirecting viewers to sites where they can purchase the items they used to buy from us. Follow the link "Home"

The "Information zone" consists of articles produced as background tutorials on subjects of interest to those designing new products. As different CPUs have became available this has lead to new development techniques and in particular to new ways of communicating between nodes.

Home

Information Zone

Powerful CMX Functions:

TASK MANAGEMENT		RESOURCE MANAGEMENT
Create a task		Get a resource
Remove a task		Reserve a resource, with time-out
Start a task		Release a resource
Suspend a task, with time-out		Get, Wait, Release Semaphores
Wake a suspended task		Mutex Semaphores have priority inheritance
Forcefully wake a task
Change a task's priority		TIMER MANAGEMENT
Terminate a task early		Create a cyclic or single shot timer
Do a co-operative rescheduling		Change a cyclic timer events parameters
Disable task scheduling		Start a cyclic timer
Enable task scheduling		Restart a cyclic timer
		Restart a cyclic timer, with new initial time
EVENT MANAGEMENT		period and/or new cyclic time period
Wait on event(s), with time-out		Stop a cyclic timer
Wait on event(s), with time-out
Set an event		MEMORY MANAGEMENT
Clear an event		Create a fixed block pool
		Request free block from pool
SYSTEM MANAGEMENT		Release block back to pool
Initialise CMX		Create a circular queue
Enter CMX		Reset queue to empty
Enter interrupt		Add to top of queue
Exit interrupt		Add to bottom of queue
Enter power down mode		Remove from top of queue
		Remove from bottom of queue
MESSAGE MANAGEMENT
Get a message		UART MANAGEMENT
Wait for a message, with time-out		Initialise UART
Send a message		Put UART char, with time-out
Send a message, wait for a reply		Put UART string, with time-out
Wake task that sent message		Get UART char, with time-out
Wait on Mailbox(s), with time-out		Get UART string, with time-out
		Update UART buffer(s)
POWER DOWN MANAGEMENT		Initialise UART buffer(s)
Handle Power Down

Task Scheduling

Many RTOS's offer only co-operative scheduling, which means that the running task has to call the scheduler to perform a task switch. This takes more work by the programmer who has to decide when the task should cause a task switch but which has the advantage of being fully deterministic. Some RTOS's offer time slicing, where each task gets to run for a period of time and then the next task will run.

A pre-emptive RTOS allows a task of higher priority that is able to run, whether from the beginning of its code or resuming its code from where it was executing last, to pre-empt the lower priority running task. This will cause the scheduler to save the context of the lower priority task (the task that was running) and restore the context of the higher priority task, so that the higher priority task, is now the running task.

Interrupts

The way in which a real time executive handles interrupts is critical to both it's ease of use and to it's efficiency. CMX's interrupt handler is written in assembler for each microprocessor and only disables interrupts.

Executing an interrupt may cause task re-scheduling. CMX's "interrupt pipe" facility allows multiple, nested interrupts which can issue most calls to the executive. This greatly simplifies writing interrupt service routines as they can easily co-operate with the high level tasks.

CMXBug Debugger

The CMX CMXBug™ debugger provides the user with the ability to view and modify different aspects of the CMX multi-tasking operating system environment, while the user's application code is running. CMXBug runs as the highest priority task using one of the target processor UART channels as the input/output device. A windows application is provided that controls CMXBug and displays its results.

The CMXBug task allows the user to select one of many options that view or change the CMX OS environment. When the CMXBug task is running it prohibits other tasks from running and freezes the task and cyclic timers so that the user gets an accurate picture of the "current state" of the system.

CMXBug allows the user to "single step" one or more system TICK, with CMXBug resuming after this "single step". CMXBug allows the user access to most of the tasks features: Cyclic timers, Resources, Mailboxes, Queues, Stacks as well as the system TICK and TIMESLICE scales. For example, the user may view a task's state (ready, waiting on what, the time remaining, etc.), it's priority, it's starting address, the events associated with the task, it's stack pointer and maximum usage. Also the user may start a task, wake a task that was waiting on some entity or stop the task.

CMXBug also provides the user with each task's percentage of RUNNING time and the amount of time, that the processor is "IDLE" with no task running. These provide a very powerful insight as to how the processor time is being spent.

CMXBug is now supplied FREE, with the CMX-RTX package, for most processors/vendors that CMX supports.

For more Information:
For CMX prices	and CPU availability.
For CMX MicroNet	The TCP/IP stack that is optimised to run on 8/16/32 bit embedded micros.
For CMX USB Stacks	Embedded Device Stacks or drivers that support USB for8/16/32 bit micros.
For CMX Options	Task Tracker, Single chip and 166 optimised versions.
Summary	Back to Real-Time Executives summary page.