The current processor has only one 8-bit external output interface which can be

Question

The current processor has only one 8-bit external output interface which can be written to with the 'out' instruction. Microcontrollers tend to have much more bits on their output interfaces. Provide a detailed explanation and justification of how the UoS educational processor could be modified to have four 8-bit output ports instead of one. In particular: explain what should be changed in the encoding of the 'out' instruction to enable four output ports; provide the new instruction encoding and give examples of this encoding; explain what should be changed in the part dealing with the external interface in cpu.vhd to have 4 output ports which can be written to with the newly defined encoding of the 'out' instruction: explain what should be changed in the port declaration of the cpu entity in cpu.vhd.

Explanation / Answer

i) The encoding should be done with the help of the monosatable multivibrator which is a pulse stretcher. The software part can be encoded with python due to its light weight, hyper theading features.

Port 0: ovs_system (internal)

Port 1: s1 ( internal)

Port 2: s1-eth1

Port 3: s1-eht2

Port 4: s2 (internal)

ii) In the external interface the summing amplifier and a monostable multivibrator should be attached to obtain the desired result.

iii) When the controller sends the flow-mod for h1 ping h2. saying if input port 2 <eth-address> 1 <etc> then output port 1. These port numbers s2 (1,2) will be mapped to openflow port do_output ( ).

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