Design and Implementation of TinyGALS: A Programming Model for ...

if there is an event in the global event queue then {
if any TinyGUYS have been modified
end if
Copy buffered values into variables.
Get token corresponding to event out of input port.
Pass value to the method linked to the input port.
else if there is a TinyOS task then {
end if
Take task out of task queue.
Run task.
4.6 Memory Usage
Figure 18: TinyGALS scheduling algorithm.
Tables 1 and 2 show the sizes of the generated functions and variables for the system
shown in Figure 17. Note that the system contains one port. Here, we assume that the
method linked to A_out writes values of type short and returns a confirmation value of
type char. Additionally, the queue connected to inport B_in is of size 50 (i.e., it holds 50
elements of type short). Thus, memory usage of a TinyGALS application is determined
mainly by the user-specified queue sizes and total number of ports in the system. The Tiny-
GALS communication framework is very lightweight, since event queues are generated as
application-specific data structures.
Table 3 compares the sizes of the TinyGALS and original TinyOS portions of the sched-
uler. The code size of the TinyGALS scheduler is only 114 bytes. For backwards compat-
ibility with TinyOS tasks, we include the original 86 byte TinyOS scheduler. If TinyOS
tasks are not used, the scheduler is about the same size as before. Refer to Section 6.1 on
why TinyOS tasks are made obsolete by the TinyGALS model.
12 The queue holds 50 elements of type short.
36