Based on kernel version 3.19. Page generated on 2015-02-13 21:22 EST.
1 2 * PTP hardware clock infrastructure for Linux 3 4 This patch set introduces support for IEEE 1588 PTP clocks in 5 Linux. Together with the SO_TIMESTAMPING socket options, this 6 presents a standardized method for developing PTP user space 7 programs, synchronizing Linux with external clocks, and using the 8 ancillary features of PTP hardware clocks. 9 10 A new class driver exports a kernel interface for specific clock 11 drivers and a user space interface. The infrastructure supports a 12 complete set of PTP hardware clock functionality. 13 14 + Basic clock operations 15 - Set time 16 - Get time 17 - Shift the clock by a given offset atomically 18 - Adjust clock frequency 19 20 + Ancillary clock features 21 - One short or periodic alarms, with signal delivery to user program 22 - Time stamp external events 23 - Period output signals configurable from user space 24 - Synchronization of the Linux system time via the PPS subsystem 25 26 ** PTP hardware clock kernel API 27 28 A PTP clock driver registers itself with the class driver. The 29 class driver handles all of the dealings with user space. The 30 author of a clock driver need only implement the details of 31 programming the clock hardware. The clock driver notifies the class 32 driver of asynchronous events (alarms and external time stamps) via 33 a simple message passing interface. 34 35 The class driver supports multiple PTP clock drivers. In normal use 36 cases, only one PTP clock is needed. However, for testing and 37 development, it can be useful to have more than one clock in a 38 single system, in order to allow performance comparisons. 39 40 ** PTP hardware clock user space API 41 42 The class driver also creates a character device for each 43 registered clock. User space can use an open file descriptor from 44 the character device as a POSIX clock id and may call 45 clock_gettime, clock_settime, and clock_adjtime. These calls 46 implement the basic clock operations. 47 48 User space programs may control the clock using standardized 49 ioctls. A program may query, enable, configure, and disable the 50 ancillary clock features. User space can receive time stamped 51 events via blocking read() and poll(). One shot and periodic 52 signals may be configured via the POSIX timer_settime() system 53 call. 54 55 ** Writing clock drivers 56 57 Clock drivers include include/linux/ptp_clock_kernel.h and register 58 themselves by presenting a 'struct ptp_clock_info' to the 59 registration method. Clock drivers must implement all of the 60 functions in the interface. If a clock does not offer a particular 61 ancillary feature, then the driver should just return -EOPNOTSUPP 62 from those functions. 63 64 Drivers must ensure that all of the methods in interface are 65 reentrant. Since most hardware implementations treat the time value 66 as a 64 bit integer accessed as two 32 bit registers, drivers 67 should use spin_lock_irqsave/spin_unlock_irqrestore to protect 68 against concurrent access. This locking cannot be accomplished in 69 class driver, since the lock may also be needed by the clock 70 driver's interrupt service routine. 71 72 ** Supported hardware 73 74 + Freescale eTSEC gianfar 75 - 2 Time stamp external triggers, programmable polarity (opt. interrupt) 76 - 2 Alarm registers (optional interrupt) 77 - 3 Periodic signals (optional interrupt) 78 79 + National DP83640 80 - 6 GPIOs programmable as inputs or outputs 81 - 6 GPIOs with dedicated functions (LED/JTAG/clock) can also be 82 used as general inputs or outputs 83 - GPIO inputs can time stamp external triggers 84 - GPIO outputs can produce periodic signals 85 - 1 interrupt pin 86 87 + Intel IXP465 88 - Auxiliary Slave/Master Mode Snapshot (optional interrupt) 89 - Target Time (optional interrupt)