CONFIG_SYS_CLOCK_TICKS_PER_SEC:

This option specifies the frequency of the system clock in Hz.

Depending on the choice made, an amount of possibly expensive math must occur when converting ticks to milliseconds and vice-versa. Some values are optimized, and yield significantly less math.

The optimal values from a computational point-of-view are 1000, 500, 250 and 125, since in these cases there is either no computation required, or it is all done via bit-shifting. These also give a granularity from 1ms to 8ms.

Other good values are 100, 50, 25, 20 and 10. In this case, some math is required but is minimized. These are also values that necessitate a reduced number of clock interrupts per second, at the cost of granularity (10ms to 100ms).

All other values require some extensive 64-bit math, and in some configurations even require calls to compiler built-in functions, and can require a non-trivial extra amount of stack space (e.g. around 80 bytes on x86).

Using the legacy API also incurs an extra penalty, since when asking for a timeout, a translation is made from ticks to milliseconds to call the native kernel APIs, and then another translation is made back to ticks, since the kernel is tick-based.

Symbol:

SYS_CLOCK_TICKS_PER_SEC
Type:

int
Value:

“100”
User value:

(no user value)
Visibility:

“y”
Is choice item:

false
Is defined:

true
Is from env.:

false
Is special:

false
Prompts:
  • “System tick frequency (in ticks/second)”
Default values:
  • 100 (value: “n”)
  • Condition: (none)
Selects:

(no selects)
Reverse (select-related) dependencies:
 

(no reverse dependencies)
Additional dependencies from enclosing menus and ifs:
 

(no additional dependencies)
Locations:
  • ../kernel/Kconfig:404