Not sure the plumbing is consistent with how it used to be.
APB4 used to be fractional from the AHB clock (M4 CPU), so M7 400 MHz, AHB 200 MHz, APB4 100 MHz.
Should be possible to get 150 MHz M4, with 75 MHz APB4 using the same relationships.
I suspect the paper relates to electromigration exacerbated by speed and temperature.
As I recollect the early H7's could hit >500 MHz in nominal conditions, vs 400 MHz spec, later revised upward to the 480 MHz on the V-Step
/**
* @brief System Clock Configuration
* The system Clock is configured as follow :
* System Clock source = PLL (HSE BYPASS)
* SYSCLK(Hz) = 400000000 (CPU Clock)
* HCLK(Hz) = 200000000 (Cortex-M4 CPU, Bus matrix Clocks)
* AHB Prescaler = 2
* D1 APB3 Prescaler = 2 (APB3 Clock 100MHz)
* D2 APB1 Prescaler = 2 (APB1 Clock 100MHz)
* D2 APB2 Prescaler = 2 (APB2 Clock 100MHz)
* D3 APB4 Prescaler = 2 (APB4 Clock 100MHz)
* HSE Frequency(Hz) = 8000000
* PLL_M = 4
* PLL_N = 400
* PLL_P = 2
* PLL_Q = 4
* PLL_R = 2
* VDD(V) = 3.3
* Flash Latency(WS) = 4
* @PAram None
* @retval None
*/
static void SystemClock_Config(void)
{
RCC_ClkInitTypeDef RCC_ClkInitStruct = {0};
RCC_OscInitTypeDef RCC_OscInitStruct = {0};
HAL_StatusTypeDef ret = HAL_OK;
/*!< Supply configuration update enable */
HAL_PWREx_ConfigSupply(PWR_DIRECT_SMPS_SUPPLY);
/* The voltage scaling allows optimizing the power consumption when the device is
clocked below the maximum system frequency, to update the voltage scaling value
regarding system frequency refer to product datasheet. */
__HAL_PWR_VOLTAGESCALING_CONFIG(PWR_REGULATOR_VOLTAGE_SCALE1);
while(!__HAL_PWR_GET_FLAG(PWR_FLAG_VOSRDY)) {}
/* Enable HSE Oscillator and activate PLL with HSE as source */
RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE;
RCC_OscInitStruct.HSEState = RCC_HSE_BYPASS;
RCC_OscInitStruct.HSIState = RCC_HSI_OFF;
RCC_OscInitStruct.CSIState = RCC_CSI_OFF;
RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON;
RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE;
RCC_OscInitStruct.PLL.PLLM = 4;
RCC_OscInitStruct.PLL.PLLN = 400;
RCC_OscInitStruct.PLL.PLLFRACN = 0;
RCC_OscInitStruct.PLL.PLLP = 2;
RCC_OscInitStruct.PLL.PLLR = 2;
RCC_OscInitStruct.PLL.PLLQ = 4;
RCC_OscInitStruct.PLL.PLLVCOSEL = RCC_PLL1VCOWIDE;
RCC_OscInitStruct.PLL.PLLRGE = RCC_PLL1VCIRANGE_2;
ret = HAL_RCC_OscConfig(&RCC_OscInitStruct);
if(ret != HAL_OK)
{
Error_Handler();
}
/* Select PLL as system clock source and configure bus clocks dividers */
RCC_ClkInitStruct.ClockType = (RCC_CLOCKTYPE_SYSCLK | RCC_CLOCKTYPE_HCLK | RCC_CLOCKTYPE_D1PCLK1 | RCC_CLOCKTYPE_PCLK1 | \
RCC_CLOCKTYPE_PCLK2 | RCC_CLOCKTYPE_D3PCLK1);
RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK;
RCC_ClkInitStruct.SYSCLKDivider = RCC_SYSCLK_DIV1;
RCC_ClkInitStruct.AHBCLKDivider = RCC_HCLK_DIV2;
RCC_ClkInitStruct.APB3CLKDivider = RCC_APB3_DIV2;
RCC_ClkInitStruct.APB1CLKDivider = RCC_APB1_DIV2;
RCC_ClkInitStruct.APB2CLKDivider = RCC_APB2_DIV2;
RCC_ClkInitStruct.APB4CLKDivider = RCC_APB4_DIV2;
ret = HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_4);
if(ret != HAL_OK)
{
Error_Handler();
}
/*
Note : The activation of the I/O Compensation Cell is recommended with communication interfaces
(GPIO, SPI, FMC, QSPI ...) when operating at high frequencies(please refer to product datasheet)
The I/O Compensation Cell activation procedure requires :
- The activation of the CSI clock
- The activation of the SYSCFG clock
- Enabling the I/O Compensation Cell : setting bit[0] of register SYSCFG_CCCSR
To do this please uncomment the following code
*/
/*
__HAL_RCC_CSI_ENABLE() ;
__HAL_RCC_SYSCFG_CLK_ENABLE() ;
HAL_EnableCompensationCell();
*/
}
