topic Re: Question about _rtc_get_time in MQX Software Solutions

Question about _rtc_get_time

rogerchaplin — Fri, 17 Oct 2014 17:55:53 GMT

I'm looking at the _rtc_get_time source code in srtc.c for MQX 4.1.0 (I'm using it in a VF65GS10 project) and believe I may have found a bug. Here is the code:

uint32_t tmp = 0;

do {

*time = tmp;

tmp = (snvs->LPSRTCMR << 17) | (snvs->LPSRTCLR >> 15) ;

} while (tmp != *time);

This is apparently trying to achieve a coherent read of the two RTC registers by continually reading them until it obtains two consecutive identical values. However, this code will always go through the do/while only one time, because of the way the tmp variable is initialized. To operate correctly the first line should instead be:

uint32_t tmp = (snvs->LPSRTCMR << 17) | (snvs->LPSRTCLR >> 15) ;

Am I missing something here?

Re: Question about _rtc_get_time

matthewkendall — Fri, 17 Oct 2014 21:33:52 GMT

On the contrary, it is guaranteed to go through the loop at least twice, because at the end of the first iteration *time will be zero and tmp will be the result of reading the registers (presumably non-zero). Thus the condition evaluates as true and it loops.

Re: Question about _rtc_get_time

rogerchaplin — Tue, 21 Oct 2014 02:02:56 GMT

Thanks for the reply. I must have been having a bad logic day.