Question
STM32WB55 Outputting a 40Mhz clock out signal
I have an IC on a board I'm designing that needs a 40Mhz clock in signal. Due to a variety of design and regulatory requirements, I would like to avoid having an external oscillator and instead use the clock out signal of the STM32WB55 on the board. I have written firmware that can output a 32Mhz signal, but I'm struggling with outputting 40Mhz:
volatile unsigned int *RCC_AHB2ENR = (unsigned int *)0x5800004C;
volatile unsigned int *RCC_CFGR = (unsigned int *)0x58000008;
volatile unsigned int *GPIOA_MODER = (unsigned int *)0x48000000;
volatile unsigned int *GPIOA_AFRH = (unsigned int *)(0x48000000 + 0x24);
#define RCC_AHB2ENR_GPIOAEN (1 << 0)
#define RCC_CFGR_MCOSEL_Pos (24)
#define RCC_CFGR_MCOSEL_SYSCLK (0x1 << RCC_CFGR_MCOSEL_Pos)
#define RCC_CFGR_MCOPRE_Pos (28)
#define RCC_CFGR_MCOPRE_DIV2 (0x1 << RCC_CFGR_MCOPRE_Pos)
void configure_clock_out() {
// Enable the clock for GPIOA
*RCC_AHB2ENR |= RCC_AHB2ENR_GPIOAEN;
// Configure pin A8 as alternate function (AF0)
*GPIOA_MODER &= ~(0x3 << (16)); // Reset the bits for pin A8
*GPIOA_MODER |= (0x2 << (16)); // Set the bits for pin A8 to alternate function mode
*GPIOA_AFRH &= ~0xF; // Reset the alternate function bits for pin A8
// Configure the MCO output to 32 MHz
*RCC_CFGR &= ~(RCC_CFGR_MCOSEL_SYSCLK); // Reset the MCO configuration bits
*RCC_CFGR |= (RCC_CFGR_MCOSEL_SYSCLK); // Set the MCO configuration to 32 MHz
}