Cannot read multiple Bytes from LSM9DS0 via I2C

[espruino-discuss2]

Posted at 2015-10-07 by otbe

Hi everyone,

Im currently writing a module for Sparkfuns LSM9DS0 9DOF IMU. The IMU is properly wired and works as expected. After some configuration I try to read 6 Bytes from register OUT_X_L_A (0x28). My code looks like the following:

I2C2.writeTo(ADDR, OUT_X_L_A);
var result = I2C2.readFrom(ADDR, 6);

result is an Int8Array of size 6, but it contains 6 equal values. More specific: its the value from OUT_X_L_A and all other registers (OUT_X_L_A+1, OUT_X_L_A+n) won't be read. Something like [ 13, 13, 13, 13, 13, 13 ] instead of [ 13, 28, 90, 54, 77, 1 ].
I have seen many modules for other I2C devices that work this way, but if I do:

I2C2.writeTo(ADDR, OUT_X_L_A);
var byte1 = I2C2.readFrom(ADDR, 1);
I2C2.writeTo(ADDR, OUT_X_L_A+1);
var byte2 = I2C2.readFrom(ADDR, 1);
...

it works...Does anyone have an advice for me?

Best regards
otbe

EDIT: Im using a espruino pico with 1v80 firmware. The LSM9DS0 should be capable to send multiple bytes.

[espruino-discuss2]

Posted at 2015-10-07 by DrAzzy

Not all I2C devices automatically increment the address like that - take a look at the datasheet...

Edit: Ahha! Here, pg 33, second paragraph:

In order to read multiple bytes, it is necessary to assert the most significant bit of the subaddress
field. In other words, SUB(7) must be equal to 1 while SUB(6-0) represents the
address of first register to be read.

And in sparkfun's code that's just what they do:

void LSM9DS0::I2CreadBytes(uint8_t address, uint8_t subAddress, uint8_t * dest, uint8_t count)
{  
	Wire.beginTransmission(address);   // Initialize the Tx buffer
	// Next send the register to be read. OR with 0x80 to indicate multi-read.
	Wire.write(subAddress | 0x80);     // Put slave register address in Tx buffer
	Wire.endTransmission(false);       // Send the Tx buffer, but send a restart to keep connection alive
	uint8_t i = 0;
	Wire.requestFrom(address, count);  // Read bytes from slave register address 
	while (Wire.available()) 
	{
		dest[i++] = Wire.read(); // Put read results in the Rx buffer
	}
}

[espruino-discuss2]

Posted at 2015-10-07 by otbe

Hi,

after my post I re-read the docs to verify that the LSM9DS0 is capable of block reading. Yes it is, but I overlooked something. The MSB of the register to read must be 1 for auto incrementing the address. I will give this a try later and add another post. :)

Thank you.

Edit: hehe you were faster :D