s110 and max value of app timer

Question

Hi, 
 What is the largest possible value of "MAX_VAL" for application timer given below: 
 "#define APP_TIMER_PRESCALER 0" 
 "#define M_DELAY APP_TIMER_TICKS(MAX_VAL, APP_TIMER_PRESCALER)" 
 Is it 32 bit value?

Clem Taylor · Accepted Answer

The RTC timer is only 24 bits and app_timer does all its timing modulo 2^24. So the largest value for your M_DELAY is (2^24)-1. However due to the way the modulo counting is done the max value is a bit smaller then this. The value I use is: 
 #define RTC_TICKS_BITS 24 // size of RTC[01] counter in bits 
#define TIMER_MAX_TIMEOUT \
 ((1 << RTC_TICKS_BITS) - APP_TIMER_MIN_TIMEOUT_TICKS * 10) // fudge
 
 How much time this represents is a function of the prescaler chosen. APP_TIMER_TICKS converts from miliseconds to ticks. 
 The max value in miliseconds is something like: 
 (2**24) * (APP_TIMER_PRESCALER+1) * 1000 / 32768 - fudge
 
 This works out to <512 seconds for prescaler of 0. 
 Personally I think app_timer could really use a thorough rewrite. It wouldn't take much for it to support timeout intervals longer then the roll-over period of the timer and in the process the code could be greatly simplified. Only one timer is available for the user and I need it to provide both a monotonic real time counter (which requires a small prescaler), and timeouts/time scheduled events (which requires a larger prescaler for longer intervals) .

s110 and max value of app timer

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