MCX-N947: 1 MHz clock (sirc_1mhz, clk_1M)

ygrayne — Fri, 14 Nov 2025 01:27:38 GMT

According to the block diagram on page 1221 of the reference manual for the MCX-N947, the clock 'sirc_1mhz' is always on. SysTick and CTIMER allow to select this clock, assuming 'clk-1M' is this SIRC-derived 1 MHz clock (is it?). However, neither SysTick nor CTIMER work with this clock selected. Both work with other clock selections.

Do I miss something to enable the 1 MHz clock, despite the aforementioned block diagram?

FWIW, a similar block diagram can be found in the ref manual for the MCX-A346, and on this MCU the 1 MHz clock is always on (called 'CLK_1M' there, in the diagram 'sirc_1mhz').

Thanks.

Re: MCX-N947: 1 MHz clock (sirc_1mhz, clk_1M)

Harry_Zhang — Fri, 14 Nov 2025 03:38:28 GMT

Hi @ygrayne

"According to the block diagram on page 1221 of the reference manual for the MCX-N947, the clock 'sirc_1mhz' is always on. "

No, you need to enable this clock.

SYSCON->CLOCK_CTRL |= SYSCON_CLOCK_CTRL_FRO1MHZ_CLK_ENA_MASK; /*!< Enable FRO_1M is on */

"SysTick and CTIMER allow to select this clock, assuming 'clk-1M' is this SIRC-derived 1 MHz clock (is it?)."

Yes, you are right.

I think you can refer to this code.

SYSCON->CLOCK_CTRL |= SYSCON_CLOCK_CTRL_FRO1MHZ_CLK_ENA_MASK; /*!< Enable FRO_1M is on */ CLOCK_AttachClk(kCLK_1M_to_SYSTICK0); /*!< Switch SYSTICK0 to CLK_1M */ CLOCK_AttachClk(kCLK_1M_to_CTIMER0); /*!< Switch CTIMER0 to CLK_1M */

Hope this will help you.

Harry

topic MCX-N947: 1 MHz clock (sirc_1mhz, clk_1M) in MCX Microcontrollers

MCX-N947: 1 MHz clock (sirc_1mhz, clk_1M)

Re: MCX-N947: 1 MHz clock (sirc_1mhz, clk_1M)