Arduino DUE programing

[foxetera]

I have a question about Arduino DUE programming!
I'm not sure about the structure of the following program minutes and what they represent.
Please tell me the meaning of "->" and "｜=" and why it is written like PIO_PB25B_TIOA0;.

 TC0->TC_CHANNEL[0].TC_CCR = TC_CCR_SWTRG | TC_CCR_CLKEN;

PIOB->PIO_ABSR |= PIO_PB25B_TIOA0;

[anon77222424]

I got the same question:

PIOC->PIO_SODR=(1u<<22);  //digitalWrite(RA_STP, HIGH);

I can work out most of it. I would just like to know what the "1u" means?
Is there any timing in this statement?

[MartinL]

Hi @foxetera

This line sets the SWTRIG and CLKEN bits in the TC0, channel 0's CCR (Channel Control Register).

TC0->TC_CHANNEL[0].TC_CCR = TC_CCR_SWTRG | TC_CCR_CLKEN;

The -> operator specifies a pointer to a structure.

TC0 is defined as a pointer to an address in memory, that points to the base address of the TC0's hardware registers:

#define TC0        ((Tc     *)0x40080000U) /**< \brief (TC0       ) Base Address */

Where this structure resides:

/** \brief Tc hardware registers */
#define TCCHANNEL_NUMBER 3
typedef struct {
       TcChannel TC_CHANNEL[TCCHANNEL_NUMBER]; /**< \brief (Tc Offset: 0x0) channel = 0 .. 2 */
  __O  uint32_t  TC_BCR;                       /**< \brief (Tc Offset: 0xC0) Block Control Register */
  __IO uint32_t  TC_BMR;                       /**< \brief (Tc Offset: 0xC4) Block Mode Register */
  __O  uint32_t  TC_QIER;                      /**< \brief (Tc Offset: 0xC8) QDEC Interrupt Enable Register */
  __O  uint32_t  TC_QIDR;                      /**< \brief (Tc Offset: 0xCC) QDEC Interrupt Disable Register */
  __I  uint32_t  TC_QIMR;                      /**< \brief (Tc Offset: 0xD0) QDEC Interrupt Mask Register */
  __I  uint32_t  TC_QISR;                      /**< \brief (Tc Offset: 0xD4) QDEC Interrupt Status Register */
  __IO uint32_t  TC_FMR;                       /**< \brief (Tc Offset: 0xD8) Fault Mode Register */
  __I  uint32_t  Reserved1[2];
  __IO uint32_t  TC_WPMR;                      /**< \brief (Tc Offset: 0xE4) Write Protect Mode Register */
} Tc;

In your example, the TC0 pointer points to the array TC_CHANNEL[0] member in the structure above.

However, the TC_CHANNEL[0] array item is a structure itself, containg the location of various TC channel specific hardware registers:

/** \brief TcChannel hardware registers */
typedef struct {
  __O  uint32_t TC_CCR;       /**< \brief (TcChannel Offset: 0x0) Channel Control Register */
  __IO uint32_t TC_CMR;       /**< \brief (TcChannel Offset: 0x4) Channel Mode Register */
  __IO uint32_t TC_SMMR;      /**< \brief (TcChannel Offset: 0x8) Stepper Motor Mode Register */
  __I  uint32_t Reserved1[1];
  __I  uint32_t TC_CV;        /**< \brief (TcChannel Offset: 0x10) Counter Value */
  __IO uint32_t TC_RA;        /**< \brief (TcChannel Offset: 0x14) Register A */
  __IO uint32_t TC_RB;        /**< \brief (TcChannel Offset: 0x18) Register B */
  __IO uint32_t TC_RC;        /**< \brief (TcChannel Offset: 0x1C) Register C */
  __I  uint32_t TC_SR;        /**< \brief (TcChannel Offset: 0x20) Status Register */
  __O  uint32_t TC_IER;       /**< \brief (TcChannel Offset: 0x24) Interrupt Enable Register */
  __O  uint32_t TC_IDR;       /**< \brief (TcChannel Offset: 0x28) Interrupt Disable Register */
  __I  uint32_t TC_IMR;       /**< \brief (TcChannel Offset: 0x2C) Interrupt Mask Register */
  __I  uint32_t Reserved2[4];
} TcChannel;

In your example, the TC_CCR (Channel Control Register) member is determined with the structure member operator, represented by a dot "."

This line:

PIOB->PIO_ABSR |= PIO_PB25B_TIOA0;

...does a read-modify-write operation, setting the PIO_PB25B_TIOA0 bit in the PIOB->PIO_ABSR regsiter without affecting the other bits in the register.

To clear the same bit requires the bitwise ANDing of the register with the negated PIO_PB25B_TIOA0 definition:

PIOB->PIO_ABSR &= ~PIO_PB25B_TIOA0;

The SAM3X8E mircocontroller hardware register definitions on my Windows machine are located at:

C:\Users\Computer\AppData\Local\Arduino15\packages\arduino\hardware\sam\1.6.12\system\CMSIS\Device\ATMEL\sam3xa\include

[foxetera]

Thank you, that was a very clear explanation.