diff options
Diffstat (limited to 'nuttx/sched/Kconfig')
| -rw-r--r-- | nuttx/sched/Kconfig | 32 |
1 files changed, 22 insertions, 10 deletions
diff --git a/nuttx/sched/Kconfig b/nuttx/sched/Kconfig index 07d1194da..54cb698d7 100644 --- a/nuttx/sched/Kconfig +++ b/nuttx/sched/Kconfig @@ -65,21 +65,33 @@ config SCHED_TICKLESS additional plaform specific interfaces that must be provided as defined include/nuttx/arch.h -config MSEC_PER_TICK +config USEC_PER_TICK int "Milliseconds per system timer tick" - default 10 if !SCHED_TICKLESS - default 1 if SCHED_TICKLESS + default 10000 if !SCHED_TICKLESS + default 100 if SCHED_TICKLESS ---help--- - The default system timer is 100Hz or MSEC_PER_TICK=10. This setting - may be defined to inform NuttX that the processor hardware is providing - system timer interrupts at some interrupt interval other than 10 msec. + In the "normal" configuration where system time is provided by a + periodic timer interrupt, the default system timer is expected to + run at 100Hz or USEC_PER_TICK=10000. This setting must be defined + to inform of NuttX the interval that the the processor hardware is + providing system timer interrupts to the OS. If SCHED_TICKLESS is selected, then there are no system timer - interrupts. In this case, MSEC_PER_TICK does not control any timer + interrupts. In this case, USEC_PER_TICK does not control any timer rates. Rather, it only determines the resolution of time reported by clock_systimer() and the resolution of times that can be set for - certain delays including watchdog timers and delayed work. In these - cases it is better to have the MSEC_PER_TICK as low as possible. + certain delays including watchdog timers and delayed work. In this + case there is a tradeoff: It is better to have the USEC_PER_TICK as + low as possible for higher timing resolution. However, the the time + is currently held in 'unsigned int' on some systems, this may be + 16-bits but on most contemporary systems it will be 32-bits. In + either case, smaller values of USEC_PER_TICK will reduce the range + of values that delays that can be represented. So the tradeoff is + between range and resolution (you could also modify the code to use + a 64-bit value if you really want both). + + The default, 100 microseconds, will provide for a range of delays + up to 120 hours. if !SCHED_TICKLESS @@ -101,7 +113,7 @@ config SYSTEM_TIME64 default n ---help--- The system timer is incremented at the rate determined by - MSEC_PER_TICK, typically at 100Hz. The count at any given time is + USEC_PER_TICK, typically at 100Hz. The count at any given time is then the "uptime" in units of system timer ticks. By default, the system time is 32-bits wide. Those defaults provide a range of about 13.6 years which is probably a sufficient range for "uptime". |