Linux Xenomai UAV Sensor platform.

Transcription

1 Linux Xenomai UAV Sensor platform. Hard real time sensor platform for: MSPIL (Mobile Sensor Platform Innovation Lab) AMOS (Autonomous Marine Operations and Systems) AUV (Autonomous Underwater Vehicle) UAV (Unmanned Aerial Vehicle) Strategic Institute Projects (SIP) Terje Frøysa Technology for a better society 1

2 Sensor system hardware IDI Sensors for UAV/AUV GPS (Global Positioning System) / GLONASS (GLObal NAvigation Satellite System) Tactical Grade Ten Degrees of Freedom Inertial Sensor (IMU) Gyro meter/barometer/magnetometer Swarm Radio (intra swarm position/communication) GPS GPS Gyro meter Barometer Magnetometer Processor Swarm Radio Technology for a better society 2

3 Prosessor and OS IDI Requirements Hard real time Multi tasking Sufficient I/O capabilities Sufficient computing power Low weight Embedded prosessor (COTS) Beaglebone Black (Sitara 1GHz Cortex A8) Open source design. Hard real time? OS Linux (preferred over commercial OS'es) Versatile, open source, large community. No hard real time (1 25ms latency) Xenomai (Provides hard real time to Linux) Technology for a better society 3

4 Linux Architectures Real time Linux Xenomai Device driver Spesific Hardware processes User process Kernel process OS kernel Hardware Abstraction Layer (HAL) CPU + motherboard Xenomai tasks Xenomai services Real time device driver Spesific Hardware processes Xenomai kernel Linux threads/processes Linux services OS kernel Hardware Abstraction Layer (HAL) ADEOS (Interrupt pipeline) CPU + motherboard device driver Spesific Hardware processes User mode Software Hardware Obtaining real time by introducing A micro kernel module. An interrupt pipeline. A real time device driver standard (RTDM). Technology for a better society 4

5 Xenomai evolution RTAI 2001 Xenomai 3 Cobalt dual core Xenomai 2 dual core Xenomai 3 Mercury single core Preemptive Linux Technology for a better society 5

6 Xenomai system calls I pipe interposition VxWorks application libvxworks glibc Xenomai offers API skins to allow porting applications from other RTOS without rewriting. Xenomai libraries are equivalent to glibc but the calls are routed to the proper skin emulator. Xenomai intercepts the regular Linux system call dispatcher by means of the I pipe. VxWorks syscalls Xenomai nucleus Linux syscalls VxWorks skin Regular Linux Sub system (I/O,VM..etc) : User space : Kernel space Technology for a better society 6

7 Xenomai and ADEOS ADEOS (Adaptive Domain Environment for Operating System) / I pipe A Linux kernel patch A resource virtualization layer. Allows Xenomai and Linux to run on the same hardware platform. Introduces the event pipeline, a chain of domains (OS'es) of decreasing priority. Interrupts & Traps (kernel events) Xenomai domain Domain events Event flow pipeline Interrupt Shield Linux (root) domain Lowest priority Virtual irq mask Technology for a better society 7

8 Software for sensor data delivery IDI GPS: 1Hz GPIO interrupts relates delivered data (UART) to time line. IMU: 450Hz GPIO interrupts relates delivered data (SPI) to time line. Gyro meter: 8Hz GPIO interrupt relates data (I2C) to time line. Magnetometer: 8Hz Barometer/Altimeter: 200Hz GPIO interrupts relates data (I2C) to time line. Swarm Radio: TBD 10Hz? Sensor Sensor Sensor irq irq irq Sensor Task Sensor Task Sensor Task Buf1 Buf2 Buf1 Buf3 Buf2 Buf1 Buf3 Buf2 Buf3 Buffer Administrator Consumer Task Dynamics Model (Kalman Filter) Actuators Swarm Radio Technology for a better society 8

9 Sensor interfacing at test Sensor Frq. Interface Speed Payload GPS 1 Hz UART 115 Kb/s 678 bytes Gyro Ca. 4 Hz I 2 C 400 Kb/s 14 bytes Magnetometer Ca. 4 Hz I 2 C 400 Kb/s 6 bytes Barometer Ca. 1 Hz I 2 C 400 Kb/s 5 bytes IMU 200 Hz SPI 746 Kb/s 78 bytes No RTDM drivers found for BeagleBone Black interfaces. Have to use standard Linux drivers (for now). RTDM drivers for sensor GPIO interrupts for precise registration of irq timing. Standard Linux UART driver Standard Linux I2C driver Modified Linux SPI driver (sub optimal and requires kernel queues for array transfer) Technology for a better society 9

10 RTDM driver for GPIO interrupts Receive irq. Read jiffies. Set semaphore. Block on Semaphore. Time to user_space info = device.rtdm_dev.device_data; info->gpio_irq_time = rtdm_clock_read_monotonic(); sem = rtdm_irq_get_arg(gpio_irq, rtdm_sem_t); if(sem->value == 0)rtdm_sem_up(sem); return RT_INTR_HANDLED; Sensor Task Initialize sensor Read irq time Read Related data from sensor Process Linux standard driver info = context->device->device_data; err = rtdm_sem_down(&(info->gpio_irq_sem)); Sensor data utime.value = info->gpio_irq_time; err = rtdm_safe_copy_to_user(user_info, buf, utime.bytes, sizeof(utime.bytes)); return sizeof(nanosecs_abs_t); Technology for a better society 10

11 Xenomai user tasks main pthread_create Linux thread Low priority Linux scheduler rt_task_create rt_task_start Xenomai task Soft real time On Linux syscall Automatic return Linux syscall Linux kernel Real time scheduler Xenomai task Xenomai syscall Xenomai kernel Hard real time Memory space: User space Kernel space High priority Technology for a better society 11

12 Xenomai real time shadow How can tasks migrate between the Linux and Xenomai domains? Linux scheduler Internal backlinks Struct task_struct Xenomai scheduler Struct xntread Higher level of integration with Linux env. compared to e.g. RTAI or RTLinux. Derives real time threads from regular Linux tasks through standard POSIX API. Inherits Linux tasks ability to invoke regular Linux services. Each scheduler uses its own data. Has access to the other scheduler's data structure. Migrates to Linux keeping its priority and scheduler policy (SCHED_FIFO). Technology for a better society 12

13 /proc/xenomai/stat and sched information CPU PID MSW CSW PF STAT %CPU NAME ROOT/ baro_task gyro_task gps_task imu_task consume_task IRQ67: [timer] IRQ135: gps_rtdm IRQ155: imu_rtdm IRQ176: gyro_rtdm IRQ188: baro_rtdm CPU PID CLASS PRI TIMEOUT TIMEBASE STAT NAME 0 0 idle -1 - master R ROOT/ rt 60 - master W baro_task rt 50 - master W gyro_task rt 50 - master W gps_task rt 70 - master W imu_task rt 40 20ms368us master D consume_task MSW = Mode switches: primary >secondary/secondary >primary CSW = Context switches (operated by Xenomai for real time threads, kernel + user space). PF = Page Faults Technology for a better society 13

14 Timing measurements At time: 521 seconds Baro [0] irqs: 527, period ms, min_time ms, max_time ms, Jitter: / ms Gyro [1] irqs: 2047, period ms, min_time ms, max_time ms, Jitter: / ms GPS [2] irqs: 512, period ms, min_time ms, max_time ms, Jitter: / ms IMU [3] irqs: , period ms, min_time ms, max_time ms, Jitter: / ms Consumer cnts: 6497, period ms, min_time ms, max_time ms, Jitter: / ms About irq's: (Missed irq time is from start of measurement) Baro [0] irqs: 527, missed irqs: 0, at: Gyro [1] irqs: 2047, missed irqs: 0, at: GPS [2] irqs: 512, missed irqs: 0, at: IMU [3] irqs: , missed irqs: 1, at: s, About kernel-to-user space latencies: Baro: mean ms, min_time ms, max_time ms, Jitter: / ms Gyro: mean ms, min_time ms, max_time ms, Jitter: / ms GPS.: mean ms, min_time ms, max_time ms, Jitter: / ms IMU.: mean ms, min_time ms, max_time ms, Jitter: / ms About I/O latencies: Baro: mean ms, min_time ms, max_time ms, Jitter: / ms Gyro: mean ms, min_time ms, max_time ms, Jitter: / ms GPS.: mean ms, min_time ms, max_time ms, Jitter: / ms IMU.: mean ms, min_time ms, max_time ms, Jitter: / ms The standard Linux SPI driver does not meet the requirements of the IMU sensor. IDI Technology for a better society 14

15 Does the sensor platform provide hard real time? Linux Xenomai will most probably provide sufficient hard real time for an UAV sensor platform. With proper RTDM drivers it would perform even better. Thank you! Technology for a better society 15