| 4.4 Model 4: Final Windows CE port
Model 4 is a hybrid model which judiciously uses main memory and secondary storage (disc) to obtain the optimal performance. Model 3 if implemented on a Flash RAM will give better performance but still the performance can be enhanced by using this hybrid approach.
4.4.1 Approach
This model does two important additions to the last model and attempts to increase the performance. The additions are the following:
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The token list which was stored on the disc in last model will be stored in main memory so that the access will take less time. Since Embedded Shruti is built on Microsoft Foundation Classes for Windows CE, a number of MFC utility classes can be used to maintain a hash structure of the tokens. The hash facilitates retrieval. In this implementation a MFC class CMap is used to store the token name and the token type keyed by a variable index which is increased accordingly.
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The other problem in model 3 was that each time a new sound file is accessed from the database, disc access time is needed. A cache structure is implemented to speed up sound file access. The cache structure stores N number of sound files on the main memory. N is selected according to the application. Typically N can be 20 sound files. When a new file is required first of all the cache is checked whether the file is there in the cache or not. If the file is available then the disc access time is not required. If the file is not available the file is brought from the database on disc and it will be saved in the cache. If the cache is full then an appropriate cache replacement strategy like Least Recently Used Algorithm (LRU) is used. The victim sound file will be chosen and removed from the cache. In its place the new sound file will be kept.
The modifications suggested will optimally use the Random Access Memory and the secondary disc so that Embedded Shruti gives the ideal performance. Till now the models are tested on Pocket-PC emulator and as mentioned in the API reference of the Pocket-PC, the performance of the software on real Pocket-PC will be better than the performance on the emulator.
This chapter will conclude with a graphical view of the model 4. The next chapter will give the performance comparison of different models on some input string. Since the input string remains same the time taken by different models will clearly differentiate between the performances of the implementations.
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