Root/
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) |
90 |
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