FDCAN->CKDIV vs FDCAN_CONFIG->CKDIV

[Uwe Bonnes]

rm0456 describes CKDIV belonging to the FDCAN register structure, However the actual header in the cmsis_device_u5 repo make it a member of the FDCAN_Config_TypeDef. This is missleading!

Probably FDCAN_Config_TypeDef. is some structure found in the MCAN IP. There is no description of FDCAN_Config in the reference manual. A description is welcome,

[Andrew Neil]

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@Uwe Bonnes wrote:

rm0456 describes CKDIV belonging to the FDCAN register structure, However the actual header in the cmsis_device_u5 repo make it a member of the FDCAN_Config_TypeDef. This is missleading!,

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Is it?

The RM calls it "FDCAN CFG Clock Divider" - so FDCAN_Config_TypeDef doesn't seem an unreasonable name?

https://www.st.com/resource/en/reference_manual/rm0456-stm32u5-series-armbased-32bit-mcus-stmicroelectronics.pdf#page=3082

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@Uwe Bonnes wrote:

Probably FDCAN_Config_TypeDef. is some structure found in the MCAN IP. ,

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Use your IDE's 'Go To Definition' feature to find it.

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@Uwe Bonnes wrote:

There is no description of FDCAN_Config in the reference manual. 

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Well, the RM describes the hardware - not the software.

[Uwe Bonnes]

From 70.4.37, it could be expected that FDCAN1 -> CKDIV resolves against the device header. But it does not resolve:

...

#include <stm32u355xx.h>

...

FDCAN1 -> CKDIV = 0xa;

> arm-none_eabi_gcc ...

/devel/stm32u5_fdcan/lv2_splitter_u535/../fdcan.c:378:12: error: 'FDCAN_GlobalTypeDef' has no member named 'CKDIV'
378 | FDCAN1 -> CKDIV = 0xa; //divide by 20
       |                ^~

[mƎALLEm]

Hello,

I didn't find any definition called FDCAN_Config_TypeDef in the HAL.

Referring to the HAL implementation (HAL_FDCAN_Init()/stm32u5xx_hal_fdcan.c), this is what I can see:

  /* Configure Clock divider */
  FDCAN_CONFIG->CKDIV = hfdcan->Init.ClockDivider;

[mƎALLEm]

Ok I found it in stm32u385xx.h (nothing called stm32u355xx.h:(

typedef struct
{
  __IO uint32_t CKDIV;            /*!< FDCAN clock divider register,                            Address offset: 0x100 + 0x000 */
       uint32_t RESERVED1[128];   /*!< Reserved,                                                0x100 + 0x004 - 0x100 + 0x200 */
  __IO uint32_t OPTR;             /*!< FDCAN option register,                                   Address offset: 0x100 + 0x204 */
       uint32_t RESERVED2[58];    /*!< Reserved,                                                0x100 + 0x208 - 0x100 + 0x2EC */
  __IO uint32_t HWCFG;            /*!< FDCAN hardware configuration register,                   Address offset: 0x100 + 0x2F0 */
  __IO uint32_t VERR;             /*!< FDCAN IP version register,                               Address offset: 0x100 + 0x2F4 */
  __IO uint32_t IPIDR;            /*!< FDCAN IP ID register,                                    Address offset: 0x100 + 0x2F8 */
  __IO uint32_t SIDR;             /*!< FDCAN size ID register,                                  Address offset: 0x100 + 0x2FC */
} FDCAN_Config_TypeDef;

and:

#define FDCAN_CONFIG_BASE_NS (APB1PERIPH_BASE_NS + 0x0000A500UL)
#define FDCAN_CONFIG FDCAN_CONFIG_NS
#define FDCAN_CONFIG_NS ((FDCAN_Config_TypeDef *) FDCAN_CONFIG_BASE_NS)

PS sometimes you are speaking about STM32U3 sometimes STM32U5 .. need to keep talking about one device.

And in HAL_FDCAN_Init():

  /* Configure Clock divider */
  FDCAN_CONFIG->CKDIV = hfdcan->Init.ClockDivider;

So I didn't understand what is the issue?

[Uwe Bonnes]

Sorry for the typo. I mean <stm32u535xx.h>. U3 is not covered by rm0456.

Issue is that RM0456 talks about  FDCAN_DIV that is not defined in the device header To set the divisor FDCAN_CONFIG is needed, but this structure is not covered by rm0456. Device header and Reference manual should be in sync.

[Andrew Neil]

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@Uwe Bonnes wrote:

Issue is that RM0456 talks about  FDCAN_DIV 

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No, it talks about FDCAN_CKDIV:

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@Uwe Bonnes wrote:

that is not defined in the device header 

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CKDIV is in the header:

typedef struct
{
  __IO uint32_t CKDIV;  /*!< FDCAN clock divider register,                            Address offset: 0x100 + 0x000 */

 and the Address offset matches

[Uwe Bonnes]

Yes, CKDIV is in the headers but for the FDCAN_CONFIG register set. But the reference manual describes if for the FDCAN register set. 

  __IO uint32_t TXEFS;        /*!< FDCAN Tx Event FIFO Status register,                             Address offset: 0x0E4 */
  __IO uint32_t TXEFA;        /*!< FDCAN Tx Event FIFO Acknowledge register,                        Address offset: 0x0E8 */
} FDCAN_GlobalTypeDef;

/**
  * @brief FD Controller Area Network Configuration
  */
typedef struct
{
  __IO uint32_t CKDIV;        /*!< FDCAN clock divider register,                            Address offset: 0x100 + 0x000 */
       uint32_t RESERVED1[128];/*!< Reserved,                                               0x100 + 0x004 - 0x100 + 0x200 */
  __IO uint32_t OPTR;         /*!< FDCAN option register,                                   Address offset: 0x100 + 0x204 */
       uint32_t RESERVED2[58];/*!< Reserved,                                                0x100 + 0x208 - 0x100 + 0x2EC */
  __IO uint32_t HWCFG;        /*!< FDCAN hardware configuration register,                   Address offset: 0x100 + 0x2F0 */
  __IO uint32_t VERR;         /*!< FDCAN IP version register,                               Address offset: 0x100 + 0x2F4 */
  __IO uint32_t IPIDR;        /*!< FDCAN IP ID register,                                    Address offset: 0x100 + 0x2F8 */
  __IO uint32_t SIDR;         /*!< FDCAN size ID register,                                  Address offset: 0x100 + 0x2FC */
} FDCAN_Config_TypeDef;

 Either it is offset 0x100 of FDCAN_GlobalTypeDef or offset 0 of FDCAN_Config_TypeDef.