RTL Design & Implementation of a RISC Processor and Peripheral Multiplexer -Part II

Here is the second part of the RISC Processor Design. I have implemented this Processor as a part of my ASIC Design Lab project “Programmable Controller/Router and Peripheral Design with peripheral I/O multiplexing”. This project focuses of peripheral multiplexing to the GPIO pins of the processor in runtime. An example case will be a Pulse Width Modulated wave switching between any I/O pins during processor execution or an UART Transmitter pin routed to a pin based on board design without the need of external multiplexers.

The processor can access the peripherals via register write instructions. Similar to register file, the peripherals support two data reads and one data write simultaneously. Since I have used custom instructions, a custom Instruction Set Architecture (ISA) is also designed.

BLOCK DIAGRAM:

16-bit Instruction Format :

1. Register Instruction:

OPCODE [15:12]

DEST[11:8]

SRC_1 [7:4]

SRC_2 [3:0]

2. Immediate Instruction:

OPCODE [15:12]

DEST[11:8]

Immediate [7:0]

INSTRUCTION SET:

INSTRUCTION	OPCODE	INSTRUCTION	OPCODE
NOP	0000	NOT	0111
ADD	0001	MOV	1000
ADDI	0010	MVI	1001
SUB	0011	BC	1010
SUBI	0100	BS	1011
AND	0101	HLT	1111
OR	0110

REGISTER BANK:

The instructions that are supported by the CPU are mainly register instructions (R-type) and hence the register bank plays an important role in the execution of the instructions. There are a total of 16 registers available in the CPU all of which are 8 bits. The CPU registers (r0-r7) and peripheral registers share a common address space. Peripheral Address decoding is taken care by the peripherals themselves.