How do I define an i2c device that has multiple addresses.

[chrisstv]

I have a 2 Mbit EEPROM, normally I would configure the overlay as follows:

	m24m02: m24m02@50 {
		compatible = "atmel,at24";
		reg = <0x50>;
		size = <262144>;
		pagesize = <256>;
		address-width = <16>;  // Max address length = 16 we need 18!
		timeout = <5>;
		//label = "M24M02E";    // Label depricated.
		//wp-gpios = <&gpio0 22 (GPIO_PULL_DOWN | GPIO_ACTIVE_LOW)>;
		//supply-gpios = <&gpio0 7 GPIO_PULL_DOWN>;
		status = "okay";
	};

But the M24M02 eeprom uses 4 addresses to access 4 blocks of memory within the device, 50, 51, 52, 53.

So my question is how do I configure the overlay so that the driver can access 4 addresses depenedent of the memory address to be accessed?

Do I have to define 4 different devices?

Many thanks

Chris

[Kazi Afroza Sultana]

Hello Chris,

'' So my question is how do I configure the overlay so that the driver can access 4 addresses depenedent of the memory address to be accessed?

Do I have to define 4 different devices?'' 

This sounds correct. Looks like zephyr x_nucleo_eeprma2 board has similar way of defining eeprom.

source: sdk-zephyr/boards/shields/x_nucleo_eeprma2/x_nucleo_eeprma2.overlay at v4.1.99-ncs1-snapshot1 · nrfconnect/sdk-zephyr · GitHub

However, you need to make sure with the vendor as M24M02 eeprom is not out product.

Thanks.

BR

Kazi

[chrisstv]

Hi Kazi,

No unfortunately in that example they are actually defining 3 different size EEPROMs I guess their development kit has 3 different size devices on their PCB.

My issue is that the M24M02 is a 2 Mbit (256K) eeprom. Given eeproms have only 2 x 8 bit address bytes (16 bits) but to access 2 Mbit (256K) you need 18 bits of address.  ST use a 2 bit field in the eeprom address register for the extra 2 bits required.

Which means you have to address the eeprom at 4 different addresses (50, 51, 52, 53) each address can access 64K of the eeprom array, making a total of 256k.

Regards

Chris

[Kazi Afroza Sultana]

Hello Chris,

You can have a look this example sdk-zephyr/samples/sensor/sgp40_sht4x/boards/blackpill_f411ce.overlay at main · nrfconnect/sdk-zephyr · GitHub; which shows how to add multple slave under one bus.

[chrisstv]

Hi

Sorry, as per the previous suggestion, This shows how to specify two different devices on one bus.

I have a single device with 4 addresses.

Which means you have to address the one single eeprom at 4 different addresses (50, 51, 52, 53) each address can access 64K of the eeprom array, making a total of 256k.

Regards

Chris

[Kenneth]

Hi Chris,

Looks like the driver may actually already support this? 
https://github.com/nrfconnect/sdk-zephyr/blob/main/drivers/eeprom/eeprom_at2x.c#L236  

/**
* @brief translate an offset to a device address / offset pair
*
* It allows to address several devices as a continuous memory region
* but also to address higher part of eeprom for chips
* with more than 2^(addr_width) adressable word.
*/
static uint16_t eeprom_at24_translate_offset(const struct device *dev,
               off_t *offset)
{
  const struct eeprom_at2x_config *config = dev->config;

 

  const uint16_t addr_incr = *offset >> config->addr_width;
  *offset &= BIT_MASK(config->addr_width);

 

  return config->bus.i2c.addr + addr_incr;
}

Kenneth