Linux/AM4378: Configuring CPU frequency in U-boot

Sung-IL

Part Number: AM4378

Tool/software: Linux

Dear Team,

For checking and changing Cortex-A9 CPU frequency in u-boot, refer to the below files:

u-boot/arch/arm/cpu/armv7/am33xx/clock_am43xx.c
u-boot/arch/arm/cpu/armv7/omap-common/clocks-common.c
u-boot/board/ti/am43xx/board.c

You can check registers PRCM_CM_CLKSEL_DPLL_MPU (0x44DF2800 + 0x560) and PRCM_CM_DIV_M2_DPLL_MPU (0x44DF2800 + 0x570) from the u-boot prompt with "md" command and thus get M,N and M2 values. Then you can calculate the CPU frequency according to the formula provided in AM437x TRM (section 6.6.3 ADPLLS).

You need also define what is the DPLL_MPU input frequency. It is based on main OSC frequency, which is 24MHz on the TI EVM.

Although I checked in TRM, I'm confusing and I would confirm if my understanding is right.

Is CPU frequency same as CLKOUT in the below Table 6-17. of AM437x TRM(Rev.H)?

e.g. CPU frequency = CLKOUT = ((CLKINP/(N+1)) * M)/M2 ?