SWCU195A December 2024 – May 2025 CC2744R7-Q1 , CC2745P10-Q1 , CC2745R10-Q1 , CC2745R7-Q1 , CC2755R10
This mechanism calculates the time period of 1 LF clock (referred to as LFINC) and provides it to the RTC to maintain the system time across standby entry exits.
The LFINC value is of format 6b.16b us and can be from any of the following four sources :
Fixed 0x1E8000 - This value corresponds to an LF period of 30.5μs.
Filtered (average) value - This is the average value of LF clock's period measured till now.
Direct measurement value - This is the live value of LF clock's period measured using the faster ULL clock (24MHz).
MMR CKMD.LFINCOVR.LFINC - Override value when CKMD.LFINCOVR.OVERRIDE is set
There are a number of factors that determine which of the 1st three sources of LF period would be forwarded to RTC. These are mentioned below :
Whether the LF clock is running or not
Whether HFOSC tracking is active or not
Whether the LF filter has settled or not (read the read-only MMR LFCLKSTAT.FLTSETTLED)
Whether LFINCCTL.PREVENTSTBY MMR is set or not
The above 4 factors are also responsible for deciding whether the LF filter is getting updated or not. This is better explained using the truth table below.
| LFOSC running | Tracking Active | LF filter Settled | CKMD.LFINCCTL. PREVENTSTBY | LFINC Source | LFTICK Source | Filter Update |
0 | 0 | 0 | 0 | Constant (0x1E8000 i.e. 30.5us) | Untracked HFOSC/4 | No |
0 | 0 | 0 | 1 | Constant (0x1E8000 i.e. 30.5us) | Untracked HFOSC/4 | No |
0 | 0 | 1 | 0 | Constant (0x1E8000 i.e. 30.5us) | Untracked HFOSC/4 | No |
0 | 0 | 1 | 1 | Constant (0x1E8000 i.e. 30.5us) | Untracked HFOSC/4 | No |
0 | 1 | 0 | 0 | Constant (0x1E8000 i.e. 30.5us) | Tracked HFOSC/4 | No |
0 | 1 | 0 | 1 | Constant (0x1E8000 i.e. 30.5us) | Tracked HFOSC/4 | No |
0 | 1 | 1 | 0 | Constant (0x1E8000 i.e. 30.5us) | Tracked HFOSC/4 | No |
0 | 1 | 1 | 1 | Constant (0x1E8000 i.e. 30.5us) | Tracked HFOSC/4 | No |
1 | 0 | 0 | 0 | Filter | LFOSC | No |
1 | 0 | 1 | 0 | Filter | LFOSC | No |
1 | 0 | 1 | 1 | Filter | LFOSC | No |
1 | 1 | 0 | 0 | Live | LFOSC | Yes |
1 | 1 | 0 | 1 | Live | LFOSC | Yes |
1 | 1 | 1 | 0 | Live | LFOSC | Yes |
1 | 1 | 1 | 1 | Live | LFOSC | Yes |