I2C API

The ALP SDK I2C driver provides a CMSIS-Driver compatible interface for I2C master and slave communication across all E1M modules.

Header

#include "alp_i2c.h"

Initialization

#include "alp_i2c.h"

/* Get the I2C driver instance for bus 0 */
ALP_I2C_Driver_t *i2c = ALP_I2C_GetDriver(0);

/* Initialize and power on */
i2c->Initialize(i2c_event_callback);
i2c->PowerControl(ALP_POWER_FULL);

/* Configure as master, standard mode (100 kHz) */
i2c->Control(ALP_I2C_BUS_SPEED, ALP_I2C_BUS_SPEED_STANDARD);

Master Transmit

#define SENSOR_ADDR  0x48

uint8_t tx_data[] = {0x00, 0x01};  /* Register address + value */

i2c->MasterTransmit(SENSOR_ADDR, tx_data, sizeof(tx_data), false);
while (i2c->GetStatus().busy);

The xfer_pending parameter (last argument) controls the STOP condition:

• false -- Send STOP after the transfer (normal single transaction)
• true -- Do not send STOP (for repeated START sequences)

Master Receive

uint8_t reg_addr = 0x00;
uint8_t rx_data[2];

/* Write register address with repeated START */
i2c->MasterTransmit(SENSOR_ADDR, &reg_addr, 1, true);
while (i2c->GetStatus().busy);

/* Read 2 bytes from the register */
i2c->MasterReceive(SENSOR_ADDR, rx_data, 2, false);
while (i2c->GetStatus().busy);

Event Callback

void i2c_event_callback(uint32_t event)
{
    if (event & ALP_I2C_EVENT_TRANSFER_DONE) {
        /* Transfer completed successfully */
    }
    if (event & ALP_I2C_EVENT_TRANSFER_INCOMPLETE) {
        /* Slave sent NACK before all bytes transferred */
    }
    if (event & ALP_I2C_EVENT_ADDRESS_NACK) {
        /* No slave acknowledged the address */
    }
    if (event & ALP_I2C_EVENT_BUS_ERROR) {
        /* Bus error (misplaced START/STOP) */
    }
}

Bus Speed Modes

Mode	Constant	Speed
Standard	ALP_I2C_BUS_SPEED_STANDARD	100 kHz
Fast	ALP_I2C_BUS_SPEED_FAST	400 kHz
Fast Plus	ALP_I2C_BUS_SPEED_FAST_PLUS	1 MHz

API Reference

Functions

Function	Description
ALP_I2C_GetDriver()	Get driver instance for an I2C bus
Initialize()	Initialize the I2C driver with event callback
Uninitialize()	De-initialize and release resources
PowerControl()	Set power state
Control()	Configure bus speed and addressing mode
MasterTransmit()	Transmit data as bus master
MasterReceive()	Receive data as bus master
SlaveTransmit()	Transmit data as bus slave
SlaveReceive()	Receive data as bus slave
GetDataCount()	Get number of bytes transferred
GetStatus()	Get current driver status
Abort()	Abort an in-progress transfer

Events

Event	Description
ALP_I2C_EVENT_TRANSFER_DONE	Transfer completed successfully
ALP_I2C_EVENT_TRANSFER_INCOMPLETE	Transfer incomplete (NACK received)
ALP_I2C_EVENT_ADDRESS_NACK	Slave address not acknowledged
ALP_I2C_EVENT_ARBITRATION_LOST	Master lost bus arbitration
ALP_I2C_EVENT_BUS_ERROR	Bus error detected

Pull-Up Resistors

I2C requires external pull-up resistors on SDA and SCL. Recommended values:

Speed Mode	Pull-Up Resistance
Standard	4.7 kohm
Fast	2.2 kohm
Fast Plus	1 kohm

See the Design Guide for carrier board I2C layout recommendations.