RTX51 TINY: SETTING ROUND-ROBIN TIMESHARING TO 1

Information in this article applies to:

C51 Version 5.50a
C51 Version 6.00

SYMPTOMS

In CONF_TNY.A51, you may specify a value for the number of ticks each task runs in round-robin multitasking.

;
;               ; define Round-Robin Timeout in Hardware-Timer Ticks.
TIMESHARING     EQU     5       ; default is 5 ticks.
;               ;
;               ; note: Round-Robin can be disabled by using value 0.
;
;  Note:   Round-Robin Task Switching can be disabled by using '0' as
;          value for the TIMESHARING equate.

Any value other than 0 enables round-robin multitasking. However, setting TIMESHARING to a value of 1 causes problems with the real-time kernel. This value should be avoided.

CAUSE

When the value for TIMESHARING is 1, a race condition may occur when creating tasks. If a new task is created just before the next timer tick interrupt occurs, you may get a round robin time-out for the newly created and activated task. However, in this case no round-robin time switch occurs and the task runs until the next time out. This means that this task will run for 256 RTX timer ticks.

The same problem might appear when a task switch occurs due to an os_wait call in another task.

RESOLUTION

Don't set TIMESHARING to 1 for round-robin multitasking.

MORE INFORMATION

Refer to Configuration in the RTX51 Tiny User's Guide.

Last Reviewed: Sunday, July 17, 2005