Consider the I/O system shown below that has four devices all of which share a bus to communicate with the CPU. To perform an I/O transfer, a device raises its bus request line and waits to receive a bus grant signal. Each time the device receives the grant signal, the device performs one block transfer and immediately issues a request for another transfer.

a) What conditions must exist for Device 2 to receive the grant signal allowing it to perform a transfer?

b) Device 3 transmits a 512-byte block of data for each transfer. To consume a bus bandwidth of 40 MB/s, how many times per second would Device 3 have to get control of the bus?

c) Write down a logic expression that gives the Bus_Grant signal as a logic funtion of Bus_Request and Bus_Busy. Bus_grant = _________________________

Bus Grant Device 0 Device 1 Device 2 Device 3 CPU with Arbiter Bus Request Bus Busy Data Bus Bus Grant Device 0 Device 1 Device 2 Device 3 CPU with Arbiter Bus Request Bus Busy Data Bus