topic Re: i2c call back is not getting called in LPC Microcontrollers

i2c call back is not getting called

sushmasan — Wed, 07 Jan 2026 23:28:47 GMT

Hello Team,

I am working with a DAC module (MCP47FEB21A0) that is interfaced with an LPC55S69 over I²C.

I observed that I2C_MasterTransferBlocking() works correctly, but when I use I2C_MasterTransferNonBlocking(), the I²C callback is never invoked.

I2C_MasterTransferNonBlocking() is returning kStatus_Success.

For reference, I2C_MasterTransferCreateHandle() is called once during I²C initialization.

Could someone please explain why the I²C callback is not getting called when using I2C_MasterTransferNonBlocking()?

Regards,
Santhosh

Re: i2c call back is not getting called

Harry_Zhang — Thu, 08 Jan 2026 06:58:49 GMT

Hi @sushmasan

I think you can refer to the lpcxpresso55s69_lpc_i2c_interrupt_b2b_transfer_master_cm33_core0 SDK demo.

Harry

Re: i2c call back is not getting called

sushmasan — Thu, 08 Jan 2026 14:53:21 GMT

Hi @Harry_Zhang ,

Thanks for your response.

I have other sensor modules that are working with non-blocking calls.

I am using a BMP390 sensor, and the I²C communication works fine with non-blocking calls. For example, if one of the register addresses is 0x01, I assign the subaddress as shown below:

masterXfer.subaddress = (uint32_t)0x01;

However, for the DAC (MCP47FEB21A0) module, the subaddress is assigned differently:

uint8_t subAddress;
subAddress = (uint8_t)(reg_addr << 3); // Based on the MCP47FEB21A0 datasheet, the register address must be shifted left by 3
masterXfer.subaddress = (uint32_t)subAddress;

Is it going to make any difference?

Regards,
San

Re: i2c call back is not getting called

Harry_Zhang — Mon, 12 Jan 2026 03:27:23 GMT

Hi @sushmasan

I think you can try to set subaddressSize = 0 and put the DAC’s command byte(s) and data bytes directly in masterXfer.data, then start a write transfer.

Harry

Re: i2c call back is not getting called

sushmasan — Mon, 12 Jan 2026 19:18:00 GMT

Hi @Harry_Zhang ,

I even tried it,

uint8_t txData[3] = {0};

txData[0] = (uint8_t) (reg_addr << 3);

txData[1] = (uint8_t)(data >> 8); /* Data high byte */

txData[2] = (uint8_t)(data & 0xFFU); /* Data low byte */

masterXfer.data = txData;

masterXfer.dataSize = 3; /* 3 bytes total */

I have some data which is of 2 bytes, so after the adding reg addr it becomes 3 bytes.

Still I²C callback is not getting called when I use I2C_MasterTransferNonBlocking().

Regards,

San

Re: i2c call back is not getting called

sushmasan — Tue, 13 Jan 2026 15:30:09 GMT

Yesterday I replied to your message, but mistakenly I did a reply to the topic. I am not sure whether you have noticed it or not, that's why responding to your message again here.

Hi @Harry_Zhang ,

I even tried it,

uint8_t txData[3] = {0};

txData[0] = (uint8_t) (reg_addr << 3);

txData[1] = (uint8_t)(data >> 8); /* Data high byte */

txData[2] = (uint8_t)(data & 0xFFU); /* Data low byte */

masterXfer.data = txData;

masterXfer.dataSize = 3; /* 3 bytes total */

I have some data which is of 2 bytes, so after the adding reg addr it becomes 3 bytes.

Still I²C callback is not getting called when I use I2C_MasterTransferNonBlocking().

Regards,

San

Re: i2c call back is not getting called

Harry_Zhang — Mon, 19 Jan 2026 02:55:54 GMT

Hi @sushmasan

Can you share the your code so I can take a look?

Harry

Re: i2c call back is not getting called

sushmasan — Mon, 19 Jan 2026 15:56:09 GMT

Hi @Harry_Zhang ,

Please find the code snippet for your reference,

#define I2C5_BASE (0x40096000u) #define I2C5_MASTER_BASE (I2C5_BASE) #define I2C5_MASTER_CLOCK_FREQUENCY (12000000) #define I2C5_MASTER ((I2C_Type *) I2C5_MASTER_BASE) static void i2c_master_callback(I2C_Type *base, i2c_master_handle_t *handle, status_t status, void *userData) { /* Signal transfer success when received success status. */ if (status == kStatus_Success) { // Successfully completed data transfer g_MasterCompletionFlag = true; g_i2cCallBackStatus = kStatus_Success; } /* Signal transfer failure when received failure status. */ else { if(status == kStatus_I2C_Nak) { g_i2cCallBackStatus = kStatus_I2C_Nak; } else if (status == kStatus_I2C_Addr_Nak) { g_i2cCallBackStatus = kStatus_I2C_Addr_Nak; } else if (status == kStatus_I2C_ArbitrationLost) { g_i2cCallBackStatus = kStatus_I2C_ArbitrationLost; } else { g_i2cCallBackStatus = false; } } return; } bool i2c_readwrite(i2c_master_transfer_t *masterXfer) { status_t status = kStatus_Fail; status_t finalStatus = kStatus_Fail; bool retVal = false; g_MasterCompletionFlag = false; g_i2cCallBackStatus = kStatus_Fail; /* Send master non-blocking data to slave (Performing the write operation) */ /* Allowing the CPU to continue executing other tasks in parallel while the I2C transfer is being handled in the background. */ status = I2C_MasterTransferNonBlocking(I2C5_MASTER, &g_m_handle, masterXfer); PRINTF("(%s() => Wait for the data transfer to slave completion. status:%d \r\n",__func__,status); /* Wait for transfer completed. */ while (!g_MasterCompletionFlag) { } g_MasterCompletionFlag = false; // Driver-level error (could not start transfer) if(status == kStatus_Success) retVal = true; // Transfer completed else retVal = false; g_i2cCallBackStatus = kStatus_Fail; return retVal; } // THIS IS WITH I2C NON BLOCKING CALL -> CALL BACK IS NOT GETTING INVOKED. bool dac_write_reg(uint8_t reg_addr, uint16_t data) { /* The DAC needs 1 address byte + 2 data bytes. */ static i2c_master_transfer_t masterXfer = {0}; static uint8_t txData[3] = {0}; bool retVal = false; bool write_status = false; memset(&masterXfer, 0, sizeof(masterXfer)); txData[0] = (uint8_t) (reg_addr << 3); txData[1] = (uint8_t)(data >> 8); txData[2] = (uint8_t)(data & 0xFFU); masterXfer.slaveAddress = 0x60; masterXfer.direction = kI2C_Write; masterXfer.subaddress = 0; masterXfer.subaddressSize = 0; masterXfer.data = txData; masterXfer.dataSize = 3; masterXfer.flags = kI2C_TransferDefaultFlag; write_status = i2c_readwrite(&masterXfer); if(true == write_status) { PRINTF("(%s) -> I2C write PASS @line:%d \r\n",__func__,__LINE__); retVal = true; } else { PRINTF("(%s) -> I2C write failed with status %d \r\n",__func__,write_status); retVal = false; } return retVal; } // THIS IS WITH I2C BLOCKING CALL -> WORKING FINE int8_t dac_write_reg(uint8_t reg_addr, uint16_t data) { /* The DAC needs 1 address byte + 2 data bytes. */ i2c_master_transfer_t masterXfer; uint8_t txData[2]; uint8_t subAddress; memset(&masterXfer, 0, sizeof(masterXfer)); subAddress = (uint8_t)(reg_addr << 3); /* DAC reg byte */ txData[0] = (uint8_t)(data >> 8); /* Data high byte */ txData[1] = (uint8_t)(data & 0xFFU); /* Data low byte */ masterXfer.slaveAddress = 0x60; masterXfer.direction = kI2C_Write; masterXfer.subaddress = (uint32_t) subAddress; masterXfer.subaddressSize = 1; masterXfer.data = txData; masterXfer.dataSize = 2; masterXfer.flags = kI2C_TransferDefaultFlag; status_t status = I2C_MasterTransferBlocking(I2C5_MASTER, &masterXfer); if (status == kStatus_Success) { PRINTF("(%s) -> dac_write_reg PASS @line:%d \r\n",__func__,__LINE__); status = 1; } else { PRINTF("(%s) -> I2C_MasterTransferBlocking() failed with status %d \r\n",__func__,status); status = -1; } return status; } int main() { I2C_MasterGetDefaultConfig(&masterConfig); I2C_MasterInit(I2C5_MASTER, &masterConfig, I2C5_MASTER_CLOCK_FREQUENCY); I2C_MasterTransferCreateHandle(I2C5_MASTER, &g_m_handle, i2c_master_callback, NULL); dac_write_reg(0x08, 0x0001); }

Re: i2c call back is not getting called

Harry_Zhang — Thu, 22 Jan 2026 09:48:44 GMT

Hi @sushmasan

i have reviewed your code.

But I'm sorry, I couldn't find a clear error. I think you can also use an oscilloscope to check if the data transmission is correct and if the returned data is correct.

Harry