experimental retro 16 bit cpu written in verilog xilinx vivado intended for fpga Cmod S7 from Digilent
2 cycles / instruction
pre pipeline
second try at fpga verilog vivado
development continued in project zen-one
z n - r c vintage 16 bit cpu
e e e a
r g t l 64K 16 bit instructions
o a u l 64K 16 bit data
t r 16 16 bit registers
i n 64 calls stack
v 66 MHz
e
| 0 | 1 | 2 | 3 | 4 - 7 | 8-11 | 12-15|
|---|---|---|---|-----------|------|------|
| z | n | r | c | op | rega | regb |
|---|---|---|---|---|-------|------|------|--------
/ . / . / . / 0 / 0 / 0 0 0 / .... / .... / add /
/ . / . / . / 0 / 0 / 1 0 0 / .... / .... / sub /
/ . / . / . / 0 / 0 / 0 1 0 / .... / .... / or /
/ . / . / . / 0 / 0 / 1 1 0 / .... / .... / xor /
/ . / . / . / 0 / 0 / 0 0 1 / .... / .... / and /
/ . / . / . / 0 / 0 / 1 0 1 / ... / .... / not /
/ . / . / . / 0 / 0 / 0 1 1 / .... / .... / cp /
/ . / . / . / 0 / 0 / 1 1 1 / imm4 / .... / shf /
/---/---/---/---/---/-------/------/------/-------/
/ . / . / . / 0 / 1 / 0 0 0 / imm4 / .... / addi /
/ . / . / . / 0 / 1 / 1 0 0 / 0000 / .... / ldi /
/ . / . / . / 0 / 1 / 0 1 0 / src / dst / ld /
/ . / . / . / 0 / 1 / 1 1 0 / dst / src / st /
/ . / . / . / 0 / 1 / 0 0 1 / .... / .... / /
/ . / . / . / 0 / 1 / 1 0 1 / .... / .... / /
/ . / . / . / 0 / 1 / 0 1 1 / .... / .... / /
/ . / . / . / 0 / 1 / 1 1 1 / .... / .... / /
/---/---/---/---/---/-------/------/------/-------/
/ . / . / 0 / 1 / immediate 12 << 4 / call /
/ . / . / 1 / 1 / signed immediate 12 / jmp /
/---/---/---/---/---/-------/------/------/-------/
\ . \ . \ . \ 0 \ 1 \ 1 0 0 \ 0100 \ .... \ wl \
\ . \ . \ . \ 0 \ 1 \ 1 0 0 \ 0101 \ .... \ wh \
\ . \ . \ . \ 0 \ 1 \ 1 0 0 \ 0110 \ .... \ rl \
\ . \ . \ . \ 0 \ 1 \ 1 0 0 \ 0111 \ .... \ rh \
\ . \ . \ . \ 0 \ 1 \ 1 0 0 \ 1100 \ .... \ \
\ . \ . \ . \ 0 \ 1 \ 1 0 0 \ 1101 \ .... \ \
\ . \ . \ . \ 0 \ 1 \ 1 0 0 \ 1110 \ .... \ led \
\ . \ . \ . \ 0 \ 1 \ 1 0 0 \ 1111 \ imm4 \ ledi \
op : : cyc |
-----:-------:-----:--------------------------------------
0000 : add : 2 : reg[b] += reg[a]
0010 : sub : 2 : reg[b] -= reg[a]
0100 : or : 2 : reg[b] |= reg[a]
0110 : xor : 2 : reg[b] ^= reg[a]
1000 : and : 2 : reg[b] &= reg[a]
1010 : not : 2 : reg[b] = ~reg[a]
1100 : cp : 2 : reg[b] = reg[a]
1110 : shf : 2 : reg[b] >>= (imm4>=0?++imm4:-imm4)
-----:-------:-----:--------------------------------------
0001 : addi : 2 : reg[b] += (imm4>=0?++imm4:-imm4)
0011 : ldi : 4 : reg[b] = { next instruction }
0101 : ld : 2 : reg[b] = ram[a]
0111 : st : 2 : ram[a] = reg[b]
1001 : : :
1011 : : :
1101 : : :
1111 : : :
-----:-------:-----:--------------------------------------
rc : : cyc :
-----+-------+-----+--------------------------------------
01 : call : 2 : pc = imm12 << 4
11 : jmp : 2 : pc += signed imm12
-----+-------+-----+--------------------------------------
i/o
|z|n|r|c| op |rega|regb| mnemo | description
|-+-+-+-+----+----+----+-------+--------------------------------------
|.|.|.|0|1100|0100|....| wl | uart blocking write lower regs[b]
|.|.|.|0|1100|0101|....| wh | uart blocking write higher regs[b]
|.|.|.|0|1100|0110|....| rl | uart blocking read lower regs[b]
|.|.|.|0|1100|0111|....| rh | uart blocking read higher regs[b]
|.|.|.|0|1100|1100|....| |
|.|.|.|0|1100|1101|....| |
|.|.|.|0|1100|1110|....| led | sets leds to lower 4 bits of regs[b]
|.|.|.|0|1100|1111|imm4| ledi | sets leds to imm4
zn flags in instructions are compared with current flags
instruction executes according to:
* zn=11 : always
* zn=00 : positive number
* zn=10 : zero
* zn=01 : negative number
instructions with rc=10 return from call
how-to with Vivado v2023.1:
* to program device edit path to ROM in "zen-x.srcs/sources_1/new/Top.v"
* connect fpga board Cmod S7 from digilent.com
* run synthesis, run implementation, program device
* find out which tty is on the usb connected to the card (i.e. /dev/ttyUSB1)
* connect with terminal at 9600 baud, 8 bits, 1 stop bit, no parity
* button 0 is reset, click it to restart and display the prompt
* "HELLO" is the prompt
* after the tests and prompt the program enters a read / write loop (echo)
* provided ROM is meant for tests run in the simulator
programming zen-x
* use 'zasm' to compile assembler code
* see 'notes/zasm-samples/' for examples.