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

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Poll packet from receive DMA ring Push packet to Queue Queue full? Enqueue packet on Queue Pull packet from Queue Enqueue packet on transmit DMA ring N Y Drop packet (Queue drop) Figure 23: Flowchart for Click configuration shown in Figure 22. 50
pull() method of Null calls pull() on its input port, which calls the pull() method of the Queue. The Queue element dequeues the packet and returns it through the return of the pull() calls. Overhead in Click Modularity in Click results in two main sources of overhead. The first source of overhead comes from passing packets between elements. This causes one or two virtual function calls, which involves loading the relevant function pointer from a virtual function table, as well as an indirect jump through that function pointer. This overhead is avoidable – the Click distribution contains a tool to eliminate all virtual function calls from a Click configuration. The second source of overhead comes from unnecessarily general element code. The authors of [25] found that element generality had a relatively small effect on Click’s performance since not many elements in a particular configuration offered much opportunity for specialization. Comparison of Click to TinyGALS An element in Click is comparable to a component in TinyGALS in the sense that both are objects with private state. Rules in Click on connecting elements together are similar to those for connecting components in TinyGALS – push outputs must be connected exactly once, but push inputs may be connected more than once (see Sections 2.3.3 and 3). Both types of objects (Click elements and TinyGALS components) communicate with other objects via method calls. In Click, there is no funda- mental difference between push processing and pull processing in Click at the method call level of view; they are sets of method calls that differ only in name. However, the direction of control flow with respect to data flow in the two types of processing are opposite of each other. Push processing can be thought of as event-driven computation (if we ignore the polling aspect of Click), where control and data flow downstream in response to an upstream event. Pull processing can be thought of as demand-driven computation, where control flows upstream in order to compute data needed downstream. Figure 24 helps to provide a more detailed analysis of the difference in control and data 51
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Design and Implementation of TinyGA
Page 5 and 6:
Contents 1 Introduction 1 2 The Tin
Page 7: 8 Acknowledgements 60 iii
Page 10 and 11: does not require synchronization, w
Page 12 and 13: integrate subsystems that share a c
Page 14 and 15: 2 The TinyGALS Programming Model Ti
Page 16 and 17: 2.2.1 TinyGALS Components Component
Page 18 and 19: Component implementation for COUNTE
Page 20 and 21: Module definition for leds. include
Page 22 and 23: uns in a single thread of execution
Page 24 and 25: as in a normal method call. 8 The g
Page 26 and 27: nondeterministic component firing o
Page 28 and 29: module. Tokens are placed in input
Page 30 and 31: Application def. include modules{ A
Page 32 and 33: 1. The values of all internal varia
Page 34 and 35: Conditions for well-formedness Here
Page 36 and 37: Determinacy of a system without glo
Page 38 and 39: I0 q0 I1 I2 In a 1 0,0 a 1 0,0 + a2
Page 40 and 41: app_init() app_start() statevar_PAR
Page 42 and 43: the same name as the output port. T
Page 44 and 45: if there is an event in the global
Page 46 and 47: 5 Example The TinyGALS programming
Page 48 and 49: the motes as three separate modules
Page 50 and 51: Table 4: Code size comparison of BL
Page 52 and 53: gered modules in TinyGALS and tasks
Page 54 and 55: critical section to maintain data i
Page 56 and 57: and a pull port is illegal. Every p
Page 60 and 61: Click router thread TinyGALS thread
Page 62 and 63: unlike Click, the TinyGALS model do
Page 64 and 65: 6.5 Timed Multitasking Timed multit
Page 66 and 67: quiescent system state to the next
Page 68 and 69: 8 Acknowledgements I wish to thank
Page 70 and 71: [11] S. S. Bhattacharyya, E. Cheong
Page 72 and 73: [31] T. J. Mowbray, W. A. Ruh, and
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