I think I am enabling packet error checking on specific I2C reads from a peripheral device. I do this by setting CR1 bits PEC, POS, and ENPEC, then doing a HAL_I2C_Mem_Read. I get expected results from the register read. Should PEC be zero?

[TAnde.5]

I look at SR2 PEC contents (most significant 8 bits), and they always are zero. Is that normal?

[TAnde.5]

I went back and printed full SR2 register contents, and I am seeing different PEC values in the PEC bits.

Sorry, should have done that sooner...

[TAnde.5]

Another question: When using HAL_I2C_Mem_Read to read a register from an external device, I am setting a value of 2 for the number of bytes to read (16-bit register).

I am getting proper value of the register being written. But do I need to set a different value when I am also getting PEC, or is that done by the setup?

[Pavel A.]

For PEC, use the SMBUS API: HAL_SMBUS_Init etc.

https://github.com/STMicroelectronics/STM32CubeH7/blob/master/Drivers/STM32H7xx_HAL_Driver/Src/stm32h7xx_hal_smbus.c

[TAnde.5]

Is PEC not available when using HAL_I2C_Mem_Read if I have set the following bits in CR2: PEC, POS, ENPEC? Or do I need to be in SMBUS mode for PEC to be functional? Is there an appnote that explains how to make use of PEC?

I am interfacing with an external device that differs from EEPROM in the protocol.

EEPROM

Master S AD+W RA S AD+R NACK P

Slave ACK ACK ACK DATA

GAUGE

Master S AD+W RA S AD+R ACK NACK P

Slave ACK ACK ACK DATA PEC

It is my understanding that setting the POS bit in CR2 enables the Master to generate ACK prior to receiving PEC, correct?

[TAnde.5]

Sorry, formatting got messed up after pressing "Answer" button.

[TAnde.5]

Here is my code for working with PEC - it assumes that I2C is already in use, and adds code for PEC (and then subtracts...)

  // 1. Clear PE bit.

  CLEAR_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_PE);

  __asm__ __volatile__("nop");

  // 2. Set PEC bit in I2Cx_CR1 register.

  SET_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_PEC);

  __asm__ __volatile__("nop");

  /* 3. Set POS bit in I2Cx_CR1 register. */

  SET_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_POS);

  __asm__ __volatile__("nop");

  /* 4. Set PECEN bit in I2Cx_CR1 register. */

  SET_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_ENPEC);

  __asm__ __volatile__("nop");

  /* 5. Set SMBTYPE bit in I2Cx_CR1 register. */

  SET_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_SMBTYPE);

  __asm__ __volatile__("nop");

  /* 6. Set SMBUS bit in I2Cx_CR1 register. */

  SET_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_SMBUS);

  __asm__ __volatile__("nop");

  /* 7. Enable the I2C peripheral by setting the PE bit in I2Cx_CR1 register */

  SET_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_PE);

  __asm__ __volatile__("nop");

  iRet = HAL_I2C_Mem_Read(reqB->hi2c, BQ_ADDR, reg, 1, bVal, sizeof(bVal)+1,pdMS_TO_TICKS(B_I2C_TIMEOUT));

  osDelay(5); // Delay 5 milliseconds

  sr2val = reqB->hi2c->Instance->SR2;

  if(reqB->hi2c->Instance->SR1&0x1000)

  {

   DbgPrintf("PEC error\r\n");

  }

  else

  {

   DbgPrintf("PEC good, PEC=%x\r\n",sr2val);

  }

  // 1. Clear PE bit.

  CLEAR_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_PE);

  __asm__ __volatile__("nop");

  // 2. Clear PEC bit in I2Cx_CR1 register.

  CLEAR_BIT(reqBatt->hi2c->Instance->CR1, I2C_CR1_PEC);

  __asm__ __volatile__("nop");

  /* 3. Clear POS bit in I2Cx_CR1 register. */

  CLEAR_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_POS);

  __asm__ __volatile__("nop");

  /* 4. Clear ENPEC bit in I2Cx_CR1 register. */

  CLEAR_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_ENPEC);

  __asm__ __volatile__("nop");

  /* 5. Clear SMBTYPE bit in I2Cx_CR1 register. */

  CLEAR_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_SMBTYPE);

  __asm__ __volatile__("nop");

  /* 6. Clear SMBUS bit in I2Cx_CR1 register. */

  CLEAR_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_SMBUS);

  __asm__ __volatile__("nop");

  /* 7. Enable the I2C peripheral by setting the PE bit in I2Cx_CR1 register */

  SET_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_PE);

  __asm__ __volatile__("nop");

The code above works, but I am not sure if I need everything that is here. For instance, does PE need to be disabled, enabled or can I remove those?

Existing code had NOPs included - are those necessary?

[TAnde.5]

Any answers to my questions?

1. Do I need to clear/set PE bit?
2. Do I need to include NOPs between register writes?

Are there any other things regarding PEC that I need to know?

[TAnde.5]

Experimentation - NEED CONFIRMATION! I have removed NOPs and PE bit reset/set, and this appears to work.

  // 1. Set PEC bit in I2Cx_CR1 register.

  SET_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_PEC);

  /* 2. Set POS bit in I2Cx_CR1 register. */

  SET_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_POS);

  /* 3. Set PECEN bit in I2Cx_CR1 register. */

  SET_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_ENPEC);

  /* 4. Set SMBTYPE bit in I2Cx_CR1 register. */

  SET_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_SMBTYPE);

  /* 5. Set SMBUS bit in I2Cx_CR1 register. */

  SET_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_SMBUS);

  iRet = HAL_I2C_Mem_Read(reqB->hi2c, BQ_ADDR, reg, 1, bVal, sizeof(bVal)+1,pdMS_TO_TICKS(B_I2C_TIMEOUT));

  osDelay(5); // Delay 5 milliseconds

  if(reqB->hi2c->Instance->SR1&0x1000)

  {

   DbgPrintf("PEC error\r\n");

  }

  else

  {

   DbgPrintf("PEC good, PEC=%x\r\n",sr2val);

  }

  // 1. Clear PEC bit in I2Cx_CR1 register.

  CLEAR_BIT(reqBatt->hi2c->Instance->CR1, I2C_CR1_PEC);

  /* 2. Clear POS bit in I2Cx_CR1 register. */

  CLEAR_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_POS);

  /* 3. Clear ENPEC bit in I2Cx_CR1 register. */

  CLEAR_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_ENPEC);

  /* 4. Clear SMBTYPE bit in I2Cx_CR1 register. */

  CLEAR_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_SMBTYPE);

  /* 5. Clear SMBUS bit in I2Cx_CR1 register. */

  CLEAR_BIT(reqB->hi2c->Instance->CR1, I2C_CR1_SMBUS);

[Bfdgr.1]

Another question: When the use of HAL_I2C_Mem_Read to read a check in from an outside tool, I am setting a cost of 2 for the wide variety of bytes to examine here. I am getting right price of the sign up being written.