TinyOS Programming Boot Camp Part II – Tiny OS Component Design and Tools

1. TinyOS Programming Boot CampPart II – Tiny OS Component Design and Tools David Culler, Jason Hill, Robert Szewczyk, Alec Woo U.C. Berkeley 2/9/2001

2. Networked Sensor System Challenge sensors actuators • Managing multiple concurrent flows • some with real-time requirements • Very limited I/O controller hierarchy • process every bit, or perhaps byte in CPU • Asynchronous and synchronous devices • Limited storage and processing • At very low power storage network TOS Boot 2

3. TinyOS Execution Contexts Tasks events commands Interrupts Hardware TOS Boot 2

4. TinyOS Storage Model • Single shared stack • Each component has a static frame • only accessible locally (except msg buffers) • Msg buffers allocated statically by components, but shared dynamically by ownership discipline TOS Boot 2

5. TinyOS Commands and Events { ... status = TOS_CALL_COMMAND(name)(args) ... } TOS_COMMAND(name)(args) { ... return status; } TOS_EVENT(name)(args) { ... return status; } { ... status = TOS_SIGNAL_EVENT(name)(args) ... } TOS Boot 2

6. Commands • Function call across component boundary • cause action to be initiated • bounded amount of work • cannot block • always return status (0 => error) • component can refuse to perform command • share call stack and execution context • command body has access to local frame • commands may post tasks or call commands • commands may not signal events TOS Boot 2

7. Events • Upcall to notify action has occured • must do bounded (and small) amount of work • cannot block • access local frame, shares stack • Lowest-level events triggered by hardware interrupts • hardware abstraction components perform critical section and enable interrupts • Events may signal events • Events may call commands • Entire event “fountain” must stay within overall application jitter tolerance TOS Boot 2

8. initc sens_output_init /sub_output_init startc sens_output_start /sub_clock_init clocke sens_clock_event /getdata clocke datae /output sens_data_ready FSM Programming Style • Most components are essentially FSMs • Composed via events and commands • non-blocking! TOS Boot 2

9. TASKS • provide concurrency internal to a component • longer running operations • are preempted by events • able to perform operations beyond event context • may call commands • may signal events • not preempted by tasks { ... TOS_POST_TASK(name) ... } void TOS_TASK(name) { ... } TOS Boot 2

10. Typical application use of tasks • event driven data acquisition • schedule task to do computational portion char TOS_EVENT(MAGS_DATA_EVENT)(int data){ struct adc_packet* pack = (struct adc_packet*)(VAR(msg).data); printf("data_event\n"); VAR(reading) = data; TOS_POST_TASK(FILTER_DATA); ... TOS Boot 2 mags.c

11. Filter Magnetometer Data Task TOS_TASK(FILTER_DATA){ int tmp; VAR(first) = VAR(first) - (VAR(first) >> 5); VAR(first) += VAR(reading); VAR(second) = VAR(second) - (VAR(second) >> 5); VAR(second) += VAR(first) >> 5; VAR(diff) = VAR(diff) - (VAR(diff) >> 5); tmp = VAR(first) - VAR(second); if(tmp < 0) tmp = -tmp; VAR(diff) += tmp; if((VAR(diff) >> 5) > 85){ TOS_CALL_COMMAND(MAGS_LEDg_on)(); VAR(led_on) = 255; } } TOS Boot 2

12. Tasks in low-level operation • transmit packet • send command schedules task to calculate CRC • task initiated byte-level datapump • events keep the pump flowing • receive packet • receive event schedules task to check CRC • task signals packet ready if OK • byte-level tx/rx • task scheduled to encode/decode each complete byte • must take less time that byte data transfer • i2c component • i2c bus has long suspensive operations • tasks used to create split-phase interface • events can procede during bus transactions TOS Boot 2

13. High-level use of tasks • virtual machine interpreter schedules an “interpretation task” on clock event • similar for data event • may be a long running activity • utilizes many low-level components • reschedules itself on each virtual machine instruction TOS Boot 2

14. Scheduling • current sched.c is simple fifo scheduler • Bounded number of pending tasks • When idle, shuts down node except clock • Uses non-blocking task queue data structure TOS Boot 2

15. Programming tools TOS Boot 2

16. TOS compile time tools • tools/desc2objs • Generates the list of components that need to be compiled into an application • Generates “C” header files from .comp files • tools/mkheader • tools/mksuper_desc • Generates the super.h linkage file that wires components together • tools/mk_amdisp • Generates the mappings between handler ID’s and handler function names for the AM_MSG macro TOS Boot 2

17. tools/mkheader • Generates “C” header files from .comp files • Usage: mkheader component_file • Example: ./tools/mkheader APP.comp > APP.h • Looks for ACCEPTS, USES, SIGNALS, HANDLES section of comp files. TOS Boot 2

18. tools/desc2objs • Generates the list of components that need to be compiled into an application • Walks the graph of description files to determine which components are used by the application • Looks at .comp files for IMPLEMENTED_BY directives • Usage: • Desc2objs description_file • Example: • ./tools/desc2objs apps/cnt_to_leds.desc > Makefile.objs • Output: CUST_OBJS = MAGS.o system/ADC.o system/AM.o system/CLOCK.o system/LEDS.o system/MAIN.o system/PACKETOBJ.o system/RFM.o system/SEC_DED_RADIO_BYTE.o HEADER_FILES = MAGS.h system/ADC.h system/AM.h system/CLOCK.h system/LEDS.h system/MAIN.h system/PACKETOBJ.h system/RFM.h system/SEC_DED_RADIO_BYTE.h TOS Boot 2

19. tools/mksuper_desc • Generates the super.h linkage file that wires components together • Walks the graph of description files to determine which components are used by the application • Looks at .comp files for IMPLEMENTED_BY directives and types for each function. • Automatically generates fan-out code based on number and types of connections to each net. • Wires components together with #define. • Usage: mksuper_desc description_file ... TOS Boot 2

20. tools/mksuper_desc (cont.) • Treats all of the wiring lines from all the description files together. • Example Description file excerpt: GENERIC_COMM:COMM_SEND_MSG_COMMAND AM:AM_SEND_MSG CHIRP:CHIRP_SEND_MSG GENERIC_COMM:COMM_SEND_MSG • Example Output: #define COMM_SEND_MSG_COMMAND AM_SEND_MSG_COMMAND #define CHIRP_SEND_MSG_COMMAND AM_SEND_MSG_COMMAND #define AM_MSG_HANDLER_4_EVENT INT_READING_EVENT TOS Boot 2

21. tools/mk_amdisp • Generates the mappings between handler ID’s and handler function names for the AM_MSG macro • Sends AM_DISPATCH.mapping through C preprocessor and determines the function names of the active message types that are being handled. • Inserts macros that map from function name to handler number into am_dispatch.h • Usage: mk_amdisp • Output: #define INT_READING_EVENT__AM_DISPATCH 4  INT_READING_EVENT is handles message type 4. TOS Boot 2

22. All_headers.c • Used to type check across all of the component descriptions. • Compiled into a “.o” but not linked. • Will reveal errors that arise from: • Wiring the wrong functions together • Connecting incompatible components together • Mistakes in .comp files TOS Boot 2

23. Listen and Inject • tools/listen.* & tools/inject.* • Reads from the serial port and prints out packets to the screen • Linux uses .c or .java versions, Windows uses .java versions • Listen reads in packets from the UART and prints them out. • Inject sends out a single packet out the UART and then proceeds to print out data that is returned. TOS Boot 2

24. MakefilePC • You can compile TinyOS code to run on a PC • Used as a debugging tool • Verify application logic and state machine transitions before running code on Mote • Trust me, it’s worth taking the time to run it on the PC!!! • Can even debug networking applications TOS Boot 2

25. Project: build a component • Build a few nodes as sens_to_rfm to serve as data sources • Build generic_base to forward all traffic it picks up to the host • Using rfm_to_led as a starting point, construct a new application that will aggregate sensor readings and forward min,avg,max to the host • new AGGREGATE.comp and AGGREGATE.c • int reading handler might build a table of neighbor values • on change or tick, post task to compute aggregate and send new active message with aggregate • new agg.desc TOS Boot 2