I just got my NUCLEO-H723ZG board, I loaded the GPIO_InfiniteLedToggling example project, downloaded the program to the board and it worked fine. Then I added a very simple code to output the HSE clock to an MCO pin.
/* Enable the MCO1 Clock */
LL_AHB4_GRP1_EnableClock(LL_AHB4_GRP1_PERIPH_GPIOA);
/* Configure the MCO1 pin in alternate function mode */
LL_GPIO_InitTypeDef gpio_InitStruct;
gpio_InitStruct.Pin = MCO1_PIN;
gpio_InitStruct.Mode = LL_GPIO_MODE_ALTERNATE;
gpio_InitStruct.Speed = LL_GPIO_SPEED_FREQ_VERY_HIGH;
gpio_InitStruct.OutputType = LL_GPIO_OUTPUT_PUSHPULL;
gpio_InitStruct.Pull = LL_GPIO_PULL_NO;
gpio_InitStruct.Alternate = ((uint8_t)0x00); // Alt. function = MCO.
LL_GPIO_Init(MCO1_GPIO_PORT, &gpio_InitStruct);
// Enable MCO1 (Source is HSE, 8 MHz, no prescaler).
RCC->CFGR |= ((0x2 << RCC_CFGR_MCO1_Pos) | (0x0 << RCC_CFGR_MCO1PRE_Pos));
I inspected the clock output n the scope and I can see it's very jittery. I check the board schematic and found out that the HSE is a clock signal that is generated by a secondary MCU on the board which implements the ST-LinkV3 debugger, and in itself is an MCO signal. A 25MHz clock oscillator is attached to this secondary mcu and I guess the 8 MHz MCO signal is generated from this. I inspected this clock signal and it also has high jitter! The jitter is very bad, I've never even seen this much jitter from a clock signal generated by an internal RC oscillator.
I then enabled the LSE which uses the on-board 32KHz crystal as the source for the MCO output and saw that it also has considerable jitter, certainly not what I would expect coming from a clock signal generated by an external 32KHz crystal.
Is this something to be expected from an MCO output in STM32H7 devices?
