LinuxPPS

User Tools

Site Tools

Trace:
technical_information

Differences

This shows you the differences between two versions of the page.

Link to this comparison view

Next revision		Previous revision
technical_information [2018/08/29 14:06] – created giomettitechnical_information [2025/02/24 09:02] (current) – [Parallel port generator] giometti
Line 1: Line 1:
-====== RFC considerations ======+====== Technical Information ====== 
 + 
 +===== RFC considerations =====
  
 While implementing a PPS API as RFC 2783 defines and using an embedded While implementing a PPS API as RFC 2783 defines and using an embedded
Line 26: Line 28:
 into files ''/dev/pps0'', ''/dev/pps1'', etc. into files ''/dev/pps0'', ''/dev/pps1'', etc.
  
-====== PPS with USB to serial devices ======+===== PPS with USB to serial devices =====
  
 It is possible to grab the PPS from an USB to serial device. However, It is possible to grab the PPS from an USB to serial device. However,
Line 42: Line 44:
 ch341 and pl2303 examples). ch341 and pl2303 examples).
  
-====== Coding example ======+===== Coding example =====
  
 To register a PPS source into the kernel you should define a ''struct To register a PPS source into the kernel you should define a ''struct
Line 87: Line 89:
 Please see the file ''drivers/pps/clients/pps-ktimer.c'' for example code. Please see the file ''drivers/pps/clients/pps-ktimer.c'' for example code.
  
-====== SYSFS support ======+===== SYSFS support =====
  
 If the SYSFS filesystem is enabled in the kernel it provides a new class: If the SYSFS filesystem is enabled in the kernel it provides a new class:
Line 117: Line 119:
    PPS source is connected to (if it exists).    PPS source is connected to (if it exists).
  
-====== Testing the PPS support ======+===== Testing the PPS support =====
  
 In order to test the PPS support even without specific hardware you can use In order to test the PPS support even without specific hardware you can use
Line 142: Line 144:
 This is available in the **pps-tools** repository mentioned above. This is available in the **pps-tools** repository mentioned above.
  
-====== Generators ======+===== Generators =====
  
 Sometimes one needs to be able not only to catch PPS signals but to produce Sometimes one needs to be able not only to catch PPS signals but to produce
 them also. For example, running a distributed simulation, which requires them also. For example, running a distributed simulation, which requires
-computers' clock to be synchronized very tightly. One way to do this is to +computers' clock to be synchronized very tightly.
-invent some complicated hardware solutions but it may be neither necessary +
-nor affordable. The cheap way is to load a PPS generator on one of the +
-computers (master) and PPS clients on others (slaves), and use very simple +
-cables to deliver signals using parallel ports, for example.+
  
-  Parallel port cable pinout: +To do so the class pps-gen has been added. PPS generators can be 
-  pin     name    master      slave +registered in the kernel by defining a ''struct pps_gen_source_info'' as 
-  1       STROBE    *------     * +follows: 
-  2       D0        *     |     * + 
-  3       D1        *     |     * +    static struct pps_gen_source_info pps_gen_dummy_info = { 
-  4       D2        *     |     * +            .name                   = "dummy", 
-  5       D3        *     |     * +            .use_system_clock       = true, 
-  6       D4        *     |     * +            .get_time               = pps_gen_dummy_get_time, 
-  7       D5        *     |     * +            .enable                 = pps_gen_dummy_enable, 
-  8       D6        *     |     * +    }; 
-  9       D7        *     |     * + 
-  10      ACK       *     ------* +Where the ''use_system_clock'' states if the generator uses the system 
-  11      BUSY      *           * +clock to generate its pulses, or they are from a peripheral device 
-  12      PE        *           * +clock. Method ''get_time()'' is used to query the time stored into the 
-  13      SEL       *           * +generator clock, while the method ''enable()'' is used to enable or 
-  14      AUTOFD    *           * +disable the PPS pulse generation. 
-  15      ERROR     *           * + 
-  16      INIT      *           * +Then calling the function ''pps_gen_register_source()'' in your 
-  17      SELIN     *           * +initialization routine as follows creates a new generator in the 
-  18-25   GND       *-----------*+system: 
 + 
 +    pps_gen = pps_gen_register_source(&pps_gen_dummy_info); 
 + 
 +===== Generators SYSFS support ===== 
 + 
 +If the SYSFS filesystem is enabled in the kernel it provides a new class: 
 + 
 +    $ ls /sys/class/pps-gen/ 
 +    pps-gen0/  pps-gen1/  pps-gen2/ 
 + 
 +Every directory is the ID of a PPS generator defined in the system and 
 +inside of it you find several files: 
 + 
 +    $ ls -F /sys/class/pps-gen/pps-gen0/ 
 +    dev  enable  name  power/  subsystem@  system  time  uevent 
 + 
 +To enable the PPS signal generation you can use the command below: 
 + 
 +    $ echo 1 > /sys/class/pps-gen/pps-gen0/enable 
 +     
 +===== Parallel port generator ===== 
 + 
 +One way to do this is to invent some complicated hardware solutions but it 
 +may be neither necessary nor affordable. The cheap way is to load a PPS 
 +generator on one of the computers (master) and PPS clients on others 
 +(slaves), and use very simple cables to deliver signals using parallel 
 +ports, for example. 
 + 
 +Parallel port cable pinout: 
 + 
 +        pin     name    master      slave 
 +        1       STROBE    *------     * 
 +        2       D0        *     |     * 
 +        3       D1        *     |     * 
 +        4       D2        *     |     * 
 +        5       D3        *     |     * 
 +        6       D4        *     |     * 
 +        7       D5        *     |     * 
 +        8       D6        *     |     * 
 +        9       D7        *     |     * 
 +        10      ACK       *     ------* 
 +        11      BUSY      *           * 
 +        12      PE        *           * 
 +        13      SEL       *           * 
 +        14      AUTOFD    *           * 
 +        15      ERROR     *           * 
 +        16      INIT      *           * 
 +        17      SELIN     *           * 
 +        18-25   GND       *-----------*
  
 Please note that parallel port interrupt occurs only on high->low transition, Please note that parallel port interrupt occurs only on high->low transition,
Line 177: Line 224:
 using polling in the interrupt handler which actually can be done way more using polling in the interrupt handler which actually can be done way more
 precisely because interrupt handling delays can be quite big and random. So precisely because interrupt handling delays can be quite big and random. So
-current parport PPS generator implementation (''pps_gen_parport'' module) is+current parport PPS generator implementation (pps_gen_parport module) is
 geared towards using the clear edge for time synchronization. geared towards using the clear edge for time synchronization.
  
Line 184: Line 231:
 latencies. But if it is too small slave won't be able to capture clear edge latencies. But if it is too small slave won't be able to capture clear edge
 transition. The default of 30us should be good enough in most situations. transition. The default of 30us should be good enough in most situations.
-The delay can be selected using ''delay'' ''pps_gen_parport'' module parameter.+The delay can be selected using ''delay'' pps_gen_parport module parameter. 
 + 
technical_information.1535551598.txt.gz · Last modified: by giometti