SLAU847D October 2022 – May 2024 MSPM0L1105 , MSPM0L1106 , MSPM0L1227 , MSPM0L1228 , MSPM0L1228-Q1 , MSPM0L1303 , MSPM0L1304 , MSPM0L1304-Q1 , MSPM0L1305 , MSPM0L1305-Q1 , MSPM0L1306 , MSPM0L1306-Q1 , MSPM0L1343 , MSPM0L1344 , MSPM0L1345 , MSPM0L1346 , MSPM0L2227 , MSPM0L2228 , MSPM0L2228-Q1
The MFCLK provides a continuous 4MHz clock to a variety of peripherals on the device. The MFCLK 4MHz rate is always derived from the SYSOSC. As the SYSOSC frequency is not fixed (it can be configured for 32, 24, 16, or 4MHz), SYSCTL automatically applies a divider to SYSOSC to keep MFCLK at a constant 4MHz rate regardless of the current SYSOSC frequency. MFCLK can be used by peripherals such as timers and serial interfaces that require a constant clock source in RUN, SLEEP, and STOP power modes.
After a SYSRST, MFCLK is initially disabled. MFCLK can be enabled in software by setting USEMFTICK in the MCLKCFG register in SYSCTL. MFCLK is active in RUN, SLEEP, and STOP power modes only, and SYSOSC must be enabled for MFCLK to operate.
All MFCLK edges are synchronized to the main system clocks (MCLK and ULPCLK), meaning that the registers of peripherals clocked by MFCLK can be read or written to at any time without any special handling.
Peripherals can select MFCLK as their functional clock source through their respective CLKSEL mux. Not all peripherals support running from MFCLK.
When using MFCLK in STOP mode, SYSOSC can be configured to automatically switch to 4MHz (low frequency) when entering STOP mode and automatically switch back to the previously selected frequency when exiting STOP mode to RUN mode (gear shift mode). As MFCLK is a 4MHz clock source, running SYSOSC at 4MHz in STOP mode reduces power consumption when in STOP mode. To configure SYSOSC for gear shift mode, see Section 2.3.1.2.1.
When MFCLK is configured to be enabled, it is only active when SYSOSC is active and MCLK is not sourced from LFCLK. When MCLK is sourced from LFCLK, MFCLK is stopped by hardware automatically. Note that if the device is in STANDBY, MCLK is always sourced from LFCLK and MFCLK is always disabled by hardware.
Asynchronous fast clock requests, if configured, temporarily enable SYSOSC to handle specific peripheral events and activity. If MFCLK is configured to be enabled (USEMFTICK is set), then MFTICK runs when a peripheral asserts an asynchronous fast clock request.