Scratchpad memory (SPM) is popular for real-time embedded systems. Whereas caches use a memory management unit (MMU) to control which data accesses go to the fast, on-chip SRAM, SPM directly maps certain addresses to the SRAM. One advantage of SPM is that it avoids the cache¡¦s costly MMU. Another advantage is that the SPM is 100% statically predictable, whereas the variables stored in the cache depend upon the dynamic execution history. This predictability is beneficial for real-time systems which must schedule tasks to finish by fixed deadlines. To set these deadlines, system designers must determine the worst-case execution times (WCETs) of the applications. The predictability of SPM makes these WCETs easier to measure.
This thesis presents a new method for allocating stack and global data to the SPM. It is the first method to make use of the special properties of non-escaping variables so as to increase the effective size of the SPM. Our insight is that many local variables of caller functions can be temporarily swapped out of the SPM while the callee function executes.
Ours is also the first method to support profiled WCET measurements in the allocation strategy. Most previous SPM methods optimize only for the average-case execution time (ACET), despite the fact that SPMs are often used in real-time environments where the WCET is also important. This new memory allocation strategy is also the first to be WCET/ACET tunable, a feature that is particular useful for soft real-time systems.
Only one previous work considers a WCET-targeted SPM allocator. That work, however, only applies to static WCET analysis tools. Such tools are difficult to program and are not widely used. Also, they only have application to the most safety-critical of real-time systems. In contrast, our approach is the first to employ measurement-based WCET analysis (such as is most commonly used in industry) for SPM allocation.
| Identifer | oai:union.ndltd.org:NSYSU/oai:NSYSU:etd-0810109-230024 |
| Date | 10 August 2009 |
| Creators | Wu, Cheng-Ying |
| Contributors | none, Steve W. Haga, Chung-nan Lee |
| Publisher | NSYSU |
| Source Sets | NSYSU Electronic Thesis and Dissertation Archive |
| Language | English |
| Detected Language | English |
| Type | text |
| Format | application/pdf |
| Source | http://etd.lib.nsysu.edu.tw/ETD-db/ETD-search/view_etd?URN=etd-0810109-230024 |
| Rights | off_campus_withheld, Copyright information available at source archive |
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