beremiz

Modbus plugin: reset periodic activation timer when overrun occurs (delays due to communication errors, ...)

2018-06-02, Mario de Sousa
7f08b03a5d92
Parents c1298e7ffe3a
Children 8efa26af791d0f6dae98ddc5
Modbus plugin: reset periodic activation timer when overrun occurs (delays due to communication errors, ...)
1 files changed, 29 insertions(+), 21 deletions(-)
  • +29 -21
    modbus/mb_runtime.c
    • --- a/modbus/mb_runtime.c Fri Mar 24 12:07:47 2017 +0000
    +++ b/modbus/mb_runtime.c Sat Jun 02 11:56:01 2018 +0100
    @@ -292,6 +292,15 @@
    }
    +#define timespec_add(ts, sec, nsec) { \
    + ts.tv_sec += sec; \
    + ts.tv_nsec += nsec; \
    + if (ts.tv_nsec >= 1000000000) { \
    + ts.tv_sec ++; \
    + ts.tv_nsec -= 1000000000; \
    + } \
    +}
    +
    static void *__mb_client_thread(void *_index) {
    int client_node_id = (char *)_index - (char *)NULL; // Use pointer arithmetic (more portable than cast)
    @@ -362,33 +371,32 @@
    }
    }
    // Determine absolute time instant for starting the next cycle
    - // struct timespec prev_cycle;
    - // prev_cycle = next_cycle;
    - next_cycle.tv_sec += period_sec;
    - next_cycle.tv_nsec += period_nsec;
    - if (next_cycle.tv_nsec >= 1000000000) {
    - next_cycle.tv_sec ++;
    - next_cycle.tv_nsec -= 1000000000;
    - }
    - /* It probably does not make sense to check for overflow of timer.
    + struct timespec prev_cycle, now;
    + prev_cycle = next_cycle;
    + timespec_add(next_cycle, period_sec, period_nsec);
    + /* NOTE A:
    + * When we have difficulty communicating with remote client and/or server, then the communications get delayed and we will
    + * fall behind in the period. This means that when communication is re-established we may end up running this loop continuously
    + * for some time until we catch up.
    + * This is undesirable, so we detect it by making sure the next_cycle will start in the future.
    + * When this happens we will switch from a purely periodic task _activation_ sequence, to a fixed task suspension interval.
    + *
    + * NOTE B:
    + * It probably does not make sense to check for overflow of timer.
    * Even in 32 bit systems this will take at least 68 years since the computer booted
    * (remember, we are using CLOCK_MONOTONIC, which should start counting from 0
    * every time the system boots). On 64 bit systems, it will take over
    * 10^11 years to overflow.
    */
    - /*
    - if (next_cycle.tv_sec) < prev_cycle.tv_sec) {
    - // we will lose some precision by reading the time again,
    - // but it is better than the alternative...
    - clock_gettime(CLOCK_MONOTONIC, &next_cycle);
    - next_cycle.tv_sec += period_sec;
    - next_cycle.tv_nsec += period_nsec;
    - if (next_cycle.tv_nsec >= 1000000000) {
    - next_cycle.tv_sec ++;
    - next_cycle.tv_nsec -= 1000000000;
    - }
    + clock_gettime(CLOCK_MONOTONIC, &now);
    + if ( ((now.tv_sec > next_cycle.tv_sec) || ((now.tv_sec == next_cycle.tv_sec) && (now.tv_nsec > next_cycle.tv_nsec)))
    + /* We are falling behind. See NOTE A above */
    + || (next_cycle.tv_sec < prev_cycle.tv_sec)
    + /* Timer overflow. See NOTE B above */
    + ) {
    + next_cycle = now;
    + timespec_add(next_cycle, period_sec, period_nsec);
    }
    - */
    clock_nanosleep(CLOCK_MONOTONIC, TIMER_ABSTIME, &next_cycle, NULL);
    }