Reading spi_RDR in debug window is potentially harmful: This is a 
hardware register where reading has side effects!

While you are debugging SPI code, save those registers into a variable 
that you can safely read with the debugger.

Even if I read in a variable, value still remains in the register. I 
would like to know why is this issue coming. I have configured the 
atsam4e8c in master mode. Even though the address to read the chip id of 
sensor is sent, a value of 0xff is there in the receive register and not 
getting cleared during debug. Once I start a new debug session,proper 
reset value is there.
Thank you in advance.

Aditya K. wrote:
> Even though the address to read the chip id of
> sensor is sent, a value of 0xff is there in the receive register and not
> getting cleared during debug.

Why should RDR get cleared? SPI always sends and receives at the same 
time, so there will be the last transferred value in the RDR.

Do you know that you usually have to transfer a dummy value to be able 
to read from the slave?

sorry I got confused.When the RDR is read,the RDRF bit should be 
cleared. In my case RDRF bit is not set.
Yes if any data is required from the slave, a dummy value should be 
sent.
In this case,I am trying to read the chip id and also other registers of 
slave by sending its corresponding address, even though the value 
received is 0xff. Please let me know what may be the issue.