Random CAN Clock

[David Pekin]

Posted on December 29, 2017 at 21:52

Hello, I'm trying to bring up CAN on the STM32F303RE.  After banging my head against the wall, and with much help from the forum, I'm getting closer.  What I notice is that the CAN clock is not repeatable from power up to power up.  I've copied the Config_System_Clock() function from the Can Networking example from the STM32373C_Eval.  It is shown below.  The line with the 

HSEPredivValue does not compile since this platform doesn't define it.  I suspect my random CAN bus timing is because the System Clock is not configured properly.  

Has anyone experienced this?  Does anyone have a known good clock configuration that will repeatably drive the CAN bus at a known rate?  (I'd also like to know how to change the clock to vary the bus rate.)

Thanks and happy new year!

/** * @brief System Clock Configuration * The system Clock is configured as follow : * System Clock source = PLL (HSI) * SYSCLK(Hz) = 64000000 * HCLK(Hz) = 64000000 * AHB Prescaler = 1 * APB1 Prescaler = 2 * APB2 Prescaler = 1 * HSI Frequency(Hz) = 8000000 * PREDIV = RCC_PREDIV_DIV2 (2) * PLLMUL = RCC_PLL_MUL16 (16) * Flash Latency(WS) = 2 * @param None * @retval None */

static void SystemClock_Config(void)

{ RCC_ClkInitTypeDef RCC_ClkInitStruct; RCC_OscInitTypeDef RCC_OscInitStruct;

/* Enable HSE Oscillator and activate PLL with HSE as source */

RCC_OscInitStruct.OscillatorType = RCC_OSCILLATORTYPE_HSE; RCC_OscInitStruct.HSEState = RCC_HSE_ON;// RCC_OscInitStruct.HSEPredivValue = RCC_HSE_PREDIV_DIV1;     This line does not compile on STM32f303 platform RCC_OscInitStruct.PLL.PLLState = RCC_PLL_ON; RCC_OscInitStruct.PLL.PLLSource = RCC_PLLSOURCE_HSE; RCC_OscInitStruct.PLL.PLLMUL = RCC_PLL_MUL9; if (HAL_RCC_OscConfig(&RCC_OscInitStruct)!= HAL_OK) { Error_Handler(); }

/* Select PLL as system clock source and configure the HCLK, PCLK1 and PCLK2

clocks dividers */ RCC_ClkInitStruct.ClockType = (RCC_CLOCKTYPE_SYSCLK | RCC_CLOCKTYPE_HCLK | RCC_CLOCKTYPE_PCLK1 | RCC_CLOCKTYPE_PCLK2); RCC_ClkInitStruct.SYSCLKSource = RCC_SYSCLKSOURCE_PLLCLK; RCC_ClkInitStruct.AHBCLKDivider = RCC_SYSCLK_DIV1; RCC_ClkInitStruct.APB1CLKDivider = RCC_HCLK_DIV2; RCC_ClkInitStruct.APB2CLKDivider = RCC_HCLK_DIV1; if (HAL_RCC_ClockConfig(&RCC_ClkInitStruct, FLASH_LATENCY_2)!= HAL_OK) { Error_Handler(); }}

[Tesla DeLorean]

Posted on December 29, 2017 at 23:38

You should look at the SystemCoreClock value, and then have it compute the APB1/APB2 clocks.

To see what's going wrong decompose the RCC/PLL setting to determine sources.

printf('Core=%d, %d MHz\n', SystemCoreClock, SystemCoreClock / 1000000);

printf('APB1=%d\n', HAL_RCC_GetPCLK1Freq());printf('APB2=%d\n', HAL_RCC_GetPCLK2Freq());

{

RCC_OscInitTypeDef RCC_OscInitStruct; HAL_RCC_GetOscConfig(&RCC_OscInitStruct);

// Dump out Osc states

}

One could use the APB to compute prescaler and bit-quanta on the fly, but you most probably want to get to the bottom of the issue you mention first.

[David Pekin]

Posted on January 02, 2018 at 03:16

I guess I'm wondering how the clock can be somewhat random.  At this point I just want a repeatable CAN clock so I can work on send/receive between devices.  As I mentioned, I copied the ConfigSystemClock from the eval to my STM32F303re project.  Does anyone know the system clock differences between the STM32373_eval and the 303? I hope I can avoid a page by page comparison of the clock systems between the devices... I appreciate the ARB and printf() suggestions.  Unfortunately, I don't have a serial output from the 303 currently and my knowledge of the clock subsystem is seriously lacking...  

Anyone have a ConfigSystemClock function that works for the 303 handy?

Thanks

[Tesla DeLorean]

Posted on January 02, 2018 at 03:26

Sometimes the EVAL board use different crystals, and HSE_VALUE define (ie 8 MHz vs 25 MHz)

If you lack a serial port consider using the SWV (Serial Wire Viewer via the debugger's PB3-SWO connection)

I'd imagine the HAL examples for the assorted boards contain working clock configurations.

Map the internal clocks out the PA8-MCO pin so you can scope them.

You're really going to need to get some diagnostic information out to be able to trouble shoot this.

[T J]

Posted on January 02, 2018 at 13:36

did you use the cube ?  I setup the canbus inside the cube.

The CanDo unit made it very easy with its clock configurator.

[David Pekin]

Posted on January 02, 2018 at 19:33

I did not use the cube tool.   I thought I'd just work off the example projects since what I'm trying to do should be pretty simple - monitor an ADC and GPIO and read/write from the CAN bus.  I thought it would be easy.  Just getting the CAN bus almost working has been anything but.  But I'm close...  I'm hoping I can use another 303 sample project's clock setup to get a stable CAN bus clock.   I suspect that installing and coming up to speed on a new framework tool, the cube, will take a lot of time.  I may end up there if the sample code approach doesn't work..