I2C registry read after a write requires to wait (delay)

[Alessandro Balzarelli]

hello,

I'm writing a simple code on RPI0W to write a registry and then read its value (the slave is an I2C to CAN module).

bcm2835_i2c_begin (); bcm2835_i2c_setSlaveAddress (0x25); bcm2835_i2c_write (buf,1);  bcm2835_i2c_read (buf,1); printf("User Register = %X \r\n",buf[0]); bcm2835_i2c_end ();

Above code is not working unless I put a delay (i.e. usleep) between the read and write. Is it expected?  Is there a wait to know if/when the write is really completed instead of just waiting and try?

Thanks a lot!!

Alex

[mike james]

There is often a slow read problem with I2C. You can't 

know how long a device will take to respond. The solution is to either use

clock stretching or polling devices usually but not always support both.

If you know a maximum time it takes the device to respond you can just wait

longer than this and then read.

mikej 

[Alessandro Balzarelli]

Thank you Mike! I'm going to use a very short delay and do retries trying to read the register.