at24cxx v0.1.0

AT24Cxx I2C EEPROM driver.

Application scenarios

• Calibration constants and serial numbers.
• User settings that survive power loss.
• A small event log with page writes.

Contract

typedef struct {
    void *context;
    uint8_t (*write_at)(void *context, uint8_t address, uint32_t memory,
                        const uint8_t *data, uint16_t length);
    uint8_t (*read_at)(void *context, uint8_t address, uint32_t memory,
                       uint8_t *data, uint16_t length);
    void (*delay_ms)(void *context, uint16_t milliseconds);
} at24cxx_port_t;

uint8_t at24cxx_init(at24cxx_t *device, at24cxx_port_t port,
                     uint8_t i2c_address, at24cxx_type_t type);
uint8_t at24cxx_read(at24cxx_t *device, uint32_t address,
                     uint8_t *data, uint16_t length);
uint8_t at24cxx_write(at24cxx_t *device, uint32_t address,
                      const uint8_t *data, uint16_t length);

• write_at and read_at perform one I2C transaction with the memory address.
• write splits at page boundaries and waits 5 ms after each page.
• Returns 1 on success, 0 on a range error or a bus error.
• Supported types: 24C01, 24C02, 24C04, 24C08, 24C16, 24C32, 24C64,

24C128, 24C256, 24C512.

Parameters

• Page size is 8, 16, 32, 64, or 128 bytes depending on the type.
• 24C01..24C16 use a one-byte memory address; larger parts use two.
• The I2C address is 7-bit (0x50..0x57).

Memory and timing

• No allocation. write needs one page delay per page (5 ms).
• A full 24C512 write takes about 2.6 s; do it outside a control loop.
• Read has no page limit; the adapter may cap the transfer length.

Integration

at24cxx_t eeprom;
at24cxx_init(&eeprom, board_i2c_port(), 0x50, AT24C02);
uint8_t serial[8];
at24cxx_read(&eeprom, 0x00, serial, sizeof(serial));

Adapters

• The adapter adds the memory address bytes and issues a repeated start.
• Reference: LibDriver at24cxx (MIT) and the Atmel AT24Cxx datasheet.
• This implementation is original.

When not to use

• More than 64 KiB; use a flash chip or a file system.
• Frequent writes; EEPROM endurance is limited.

Verification

make test covers a page-boundary write, read-back, range rejection, and

the page delay count.

AT24C01 = 0,
AT24C02,
AT24C04,
AT24C08,
AT24C16,
AT24C32,
AT24C64,
AT24C128,
AT24C256,
AT24C512,

void *context;
uint8_t (*write_at)(void *context, uint8_t address, uint32_t memory,
const uint8_t *data, uint16_t length);
uint8_t (*read_at)(void *context, uint8_t address, uint32_t memory,
uint8_t *data, uint16_t length);
void (*delay_ms)(void *context, uint16_t milliseconds);

at24cxx_port_t port;
uint8_t i2c_address;
uint32_t capacity;
uint16_t page_size;
uint8_t address_bytes;