When performing command Erase a sector :
At the end of command , signal busy is deasserted
Did this mean that the sector erasure has been completed or
I have to check status register bit 0 which means erase in progress and wait til this bit goes low ?
The busy signal goes high when the ASMI IP core is executing a valid operation (in this case erase operation), and it goes low after the operation completes. Which configuration flash device are you referring to? For EPCS and EPCQ device. you don't require to read the status register. For EPCQL device , you can try to read the status register bit 0 to know if the erase operation is in progress or complete.
Configuration flash device used : Micron MT25QL256ABA8SEF IC FLASH Serial NOR 256MBIT Quad I/O
FPGA used : 5AGXMA1D6F31C6N
So from your answer , I only need to wait for signal BUSY to be deasserted and go to next command ?
If you are using ASMI Parallel IP, you can either just monitor the busy signal goes low (erase operation complete) or use read_status operation to read the status register bit 0. Otherwise to be safe you can use both where once the busy goes low (erase operation complete) wait at least two clock cycle, then execute the read_status operation.