Caravel User Project

Jacaranda-8: 8bit CPU

Jacaranda-8 is educational ISA for home-build CPU beginners. This project implements the microarchitecture: CHARLATAN which is a simple implementation of Jacaranda-8 ISA.The following table shows the specifications of this CPU.

Jacaranda-8

item	value
microarchitecture	CHARLATAN
data bus width	8bit
instruction bus width	8bit
memory address bus width	8bit
architecture type	harvard architecture, RISC
number of general purpose register	4
I/O	memory mapped
Interruption	enabled

Instruction type	field
reg-imm load/store	op[3:0] imm[3:0]
reg-reg mov	op[3:0] rd[1:0] rs[1:0]
reg-reg cal	op[3:0] rd[1:0] rs[1:0]
jump/branch	op[3:0] mode[1:0] rs[1:0]
reg-mem load/store	op[3:0] rd[1:0] rs[1:0]

registers	type
pc	program counter
flag	comparison flag
r0	general purpose
r1	general purpose
r2	general purpose
r3	general purpose/immediate load

Number	Instruction name	mnemonic	7	6	5	4	3	2	1	0	pesudo code
0	Move	mov rd, rs	0	0	0	0	rd_index[1]	rd_index[0]	rs_index[1]	rs_index[0]	rd[7:0] = rs[7:0], PC += 1
1	Add	add rd, rs	0	0	0	1	rd_index[1]	rd_index[0]	rs_index[1]	rs_index[0]	rd[7:0] = rd[7:0] + rs[7:0], PC += 1
2	Substruct	sub rd, rs	0	0	1	0	rd_index[1]	rd_index[0]	rs_index[1]	rs_index[0]	rd[7:0] = rd[7:0] - rs[7:0], PC += 1
3	And	and rd, rs	0	0	1	1	rd_index[1]	rd_index[0]	rs_index[1]	rs_index[0]	rd[7:0] = rd[7:0] & rs[7:0], PC += 1
4	Or	or rd, rs	0	1	0	0	rd_index[1]	rd_index[0]	rs_index[1]	rs_index[0]	rd[7:0] = rd[7:0] \| rs[7:0], PC += 1
5	Not	not rd, rs	0	1	0	1	rd_index[1]	rd_index[0]	rs_index[1]	rs_index[0]	rd[7:0] = !rs[7:0], PC += 1
6	Shift Left Logical	sll rd, rs	0	1	1	0	rd_index[1]	rd_index[0]	rs_index[1]	rs_index[0]	rd[7:0] = rd[7:0] << rs[7:0], PC += 1
7	Shift Right Logical	srl rd, rs	0	1	1	1	rd_index[1]	rd_index[0]	rs_index[1]	rs_index[0]	rd[7:0] = rd[7:0] >> rs[7:0], PC += 1
8	Shift Right Arithmetic	sra rd, rs	1	0	0	0	rd_index[1]	rd_index[0]	rs_index[1]	rs_index[0]	rd[7:0] = rd[7:0] >>> rs[7:0], PC += 1
9	Compare	cmp rd, rs	1	0	0	1	rd_index[1]	rd_index[0]	rs_index[1]	rs_index[0]	flag = rd[7:0] == rs[7:0], PC += 1
10	Jump equal	je rs	1	0	1	0	0	0	rs_index[1]	rs_index[0]	PC = flag ? rs[7:0] : PC += 1
11	Jump	jmp rs	1	0	1	1	0	0	rs_index[1]	rs_index[0]	PC = rs[7:0]
12	Load Immediate High	ldih imm	1	1	0	0	imm[3]	imm[2]	imm[1]	imm[0]	imm_register[7:4] = imm[3:0], PC += 1
13	Load Immediate Low	ldil imm	1	1	0	1	imm[3]	imm[2]	imm[1]	imm[0]	imm_register[3:0] = imm[3:0], PC += 1
14	Load	ld rd, rs	1	1	1	0	rd_index[1]	rd_index[0]	rs_index[1]	rs_index[0]	rd[7:0] = mem[rs[7:0]], PC += 1
15	Store	st rd, rs	1	1	1	1	rd_index[1]	rd_index[0]	rs_index[1]	rs_index[0]	mem[rs[7:0]] = rd[7:0], PC += 1
16	Interrupt Return	iret	1	0	1	1	0	1	0	0	PC = retaddr

project build guide

Jacaranda-8 programming guide

You can program your Jacaranda-8 machine code from the management SoC by Wishbone bus.

address	function
0x3000_0000	IMEM_WRITE
0x3000_0004	UART_CLK_FREQ

IMEM_WRITE

bits[7:0] for data that will be contained in the instruction memory.
bits[15:8] for address that indicates address in the instruction memory.

UART_CLK_FREQ

put board's clock frequency

Jacaranda MMapped I/O summary

address	description	note
255	UART FLAG REGISTER 1(UFR1)
254	UART FLAG REGISTER 2(UFR2)	read only
253	UART TX DATA(UTD)
252	UART RX DATA(URD)	read only
251	GPIO OUT
250	interrupt vector
249	GPIO IN	read only