Storage Abstractions in TinyOS 2.x

1. Storage Abstractionsin TinyOS 2.x Jonathan Hui jwhui@cs.berkeley.edu University of California, Berkeley David Gay dgay@acm.org Intel Research, Berkeley TinyOS Technology Exchange

2. Non-Volatile Storage • Flash storage becoming more widely used • “Mass” data storage • logging sensor data • network programming • event logging for debugging • Configuration data that survives • power-failure • reprogramming TinyOS Technology Exchange

3. Flash Storage Variety • STMicro M25P (NOR) • Telos rev. B, Eyes 1 • Intel StrataFlash (NOR) • iMote 2 • Atmel AT45DB (NOR) • Mica Family, Telos rev. A, Eyes 2 • But has very different characteristics TinyOS Technology Exchange

4. Technology Differences • One write per bit per erase cycle • Flash characteristics: Not used in current motes TinyOS Technology Exchange

5. Architecture • Differences + limited RAM preclude common low-level HIL interfaces (e.g. block interface) • Provide high-level storage services useful for sensor network applications • Large Objects • Small Objects • Large Sequential Objects • Separate implementations of these abstractions for each class of storage chip TinyOS Technology Exchange

6. Large Objects • Get a large object, write to each byte once in any arbitrary order, and commit. • Characteristics • Size: Large (100B to 100KB, or more) • Reads: random • Writes: random (write once) • Fault tolerance: validity check • Example Applications • Network Programming • Large Data Transfer TinyOS Technology Exchange

7. Small Objects • Maintain a small chunk of values. Requires multiple and random reads/writes. • Characteristics • Size: Small (< 100B) • Reads: random • Writes: random • Fault tolerance: writes are atomic • Failure between/during writes  no data loss • Example Applications: • Configuration data storage TinyOS Technology Exchange

8. Large Sequential Object • Some applications (e.g., low-rate data collection) may want to reliably log all their results. • Characteristics • Size: Large • Reads: sequential • Writes: sequential • Fault tolerance: user-specified commit points • Failure between/during writes  entire object is not lost • Example Applications • Logging TinyOS Technology Exchange

9. Putting It Together • Sharing the flash through Volumes, with numerical identifiers • Volumes allocated similar to using fdisk. • A utility explicitly “formats” the flash. 1) Init volume table 2) Allocate each desired volume (user specifies UID and size) 3) Commit volume table • Volume table kept in non-volatile storage. Volume 0 Volume 1 Volume 2 Volume 3 Flash TinyOS Technology Exchange

10. Putting It Together • TinyOS apps must mount volume before use. • Mount by specifying UID of volume • No unmount operation • A volume is used by at most one HIL. • Allows switching of applications while managing the sharing of flash. Small Object Large Object Log Log Volume 0 Volume 1 Volume 2 Volume 3 Flash TinyOS Technology Exchange

11. Implementation Status • Currently under development: • AT45DB – Mica family, Telos rev. A, Eyes 2 • STM25P – Telos rev. B, Eyes 1 • Alpha (incomplete, etc) code on SourceForge, in: • tinyos-2.x/tos/chips/at45db • tinyos-2.x/tos/chips/stm25p • Thanks! TinyOS Technology Exchange

12. Backup Slides TinyOS Technology Exchange

13. BlockStorage interface BlockRead { command result_t read(addr_t addr, void* dest, addr_t len); event void readDone(storage_result_t result); command result_t verify(); event void verifyDone(storage_result_t result); } interface BlockWrite { command result_t write(addr_t addr, void* source, addr_t len); event void writeDone(storage_result_t result); command result_t erase(); event void eraseDone(storage_result_t result); command result_t commit(); event void commitDone(storage_result_t result); } TinyOS Technology Exchange

14. ConfigStorage interface ConfigStorage { command result_t read(addr_t addr, void* dest, addr_t len); event void readDone(storage_result_t result); command result_t write(addr_t addr void* source, addr_t len); event void writeDone(storage_result_t result); command result_t commit(); event void commitDone(storage_result_t result); } TinyOS Technology Exchange

15. Logger interface LogRead { command result_t read(uint8_t* data, uint32_t numBytes); event void readDone(uint8_t* data, uint32_t numBytes, storage_result_t success); command result_t seek(uint32_t cookie); event void seekDone(storage_result_t success); } interface LogWrite { command result_t erase(); event void eraseDone(storage_result_t success); command result_t append(uint8_t* data, uint32_t numBytes); event void appendDone(uint8_t* data, uint32_t numBytes, storage_result_t success); command uint32_t currentOffset(); command result_t sync(); event void syncDone(storage_result_t success); } TinyOS Technology Exchange

16. Volume Management interface FStorage { command result_t init(); command result_t allocate(uint8_t id, addr_t size); command result_t allocateFixed(uint8_t id, addr_t addr, addr_t size); command result_t commit(); event void commitDone(storage_result_t result, uint8_t id); } interface Mount { command result_t mount(uint8_t id); event void mountDone(storage_result_t result, uint8_t id); } TinyOS Technology Exchange