iec850 driver when receives time accuracy N, then uses as FractionOfSecond only N bits, but shall use N+1
Summary
IEC61850 Client driver truncates all non-significant bits of received time stamp (t-attribute) from a 850-server with TimeQuality.TimeAccuracy <> 31 ('unspecified'). The driver treats the Time Accuracy value N as number of significant bits in FractionOfSeconds and then truncates all the rest bits. The TISSUE 7-2 #1435 corrects the Standard and defines that the client shall use at least N+1 bits to calculate the time stamp (milliseconds).
Description
IEC61850 Client driver truncates all non-significant bits of received time stamp (t-attribute) from a 850-server with TimeQuality.TimeAccuracy <> 31 ('unspecified'). The driver treats the Time Accuracy value N as number of significant bits in FractionOfSeconds and then truncates all the rest bits. The TISSUE 7-2 #1435 corrects the Standard and defines that the client shall use at least N+1 bits to calculate the time stamp (milliseconds).
Solution
Accuracy calculation now uses N+1 bits of received FractionsOfSecons when set to N in TimeQuality octet of t-attribute.
Information
The mistake in the Standard that the TimeAccuracy is the quantity of significant bits was resulting by some t-values in wrong milliseconds of time stamp. e.g. FractionOfSeconds = 93 F4 11h, Time Accuracy = 10:
- truncated to N=10 bits --> 93 c0 00h = 9682944 --> multiplied by 2^-24 = 0,57714843750 --> 577 ms
- truncated to N+1=11 bits --> 93 e0 00h = 9691136 --> 0,57763671875 --> rounded --> 578 ms
TISSUE #1435 corrects that at least N+1 bits are significant.
Issue Number: 35547
Fixed on Date: 12.11.2015
Versions: 7.11 0 BUILD 24090 | 7.20 0 BUILD 24121