Extend IOP16 minimal example

Overview

This is a guide to extending the minimal IOP example by adding IOP16 Peripherals to the minimal design

• This is not the same as Embedding the IOP16 into another design
• This guide requires general familiarity with IOP16 16-bit I/O CPU Design
• This example does not cover porting to a different FPGA card
  • Will need to adjust I/O pin assignments if a different FPGA is used

Steps

• Start with baseline (minimal) design
• Copy/clone baseline (minimal) design
• Build baseline (minimal) design
• Copy design to new folder
• Select/add peripherals
• Create new peripherals
• Write assembly code
• Build/test

Baseline Design

Starts from IOP example

• Similar to Arduino "Blink Sketch" and uses the following resources
  • Timer Unit - 1 second timer
    • The Timer unit can be removed if not needed
    • Timer makes Blink easier
  • On-board LED

Copy/Clone Sources

• Clone the two repositories to the same directory level since relative paths are used for source files
  • IOP16 GitHub repository
  • Design a CPU GitHub repository
• Example copies files to TestBuild folder
• There are a lot of extra files in the two unzipped folders (380MB)

Alternately download ZIP files

• Alternately you can download the two ZIP files from GitHub

• Unzip these two folders into the same folder

• Rename the folders to remove the -main from the folder path

• Result

Build Minimal Design

Start by building the minimal example in Quartus II

• Open the Project file (TestIOP16B.qpf) in Quartus II
• Relative path: ..\TestBuild\IOP16\Higher_Level_Examples\TestIOP16_Minimal

• Entities in Quartus should look like

• Build FPGA (click the blue "Start Compilation arrow)

Fix ROM File Path

• Quartus does not verify the ROM file was correct
  • Could be buried in the status messages
  • Likely need to re-point to the ROM .MIF file since Quartus II sometimes "forgets"
  • Double click on the IOP_ROM file

• Hit finish
  • Check for error message

• Re-point to the ROM file
• Make sure to select .MIF file extension

Build Again / Download

• Build again
• Should be no error messages
• Result

• Download to FPGA
• Make sure pointing to the right folder

• User LED should be blinking

Copy Design to new folder

• Copy from folder ..\TestBuild\IOP16\Higher_Level_Examples\TestIOP16_Minimal

• Copy to folder ..\TestBuild\IOP16\Higher_Level_Examples\TestIOP16_UART_Loopback

• Build (as above)

• Make sure to update ROM file (as above)
• Make sure pointing to the right folder when downloading
• Test (as above)

Select Peripherals

• Pick from Supported peripherals list

Select UART for example

• This example will add UART peripheral
  • Will set up UART in loopback

Update Memory Map

• Update Memory map in comments at start of TestIOP16B.vhd to add UART addresses

-- IOP16 MEMORY Map
-- 0X00      - KEY1 Pushbutton (R)
-- 0X00      - User LED (W)
-- 0x04-0x07 - Timer Unit
-- 0X08      - UART (Cmd/Stat) (r/w)
-- 0X09      - UART (Data) (r/w)

Add UART files to project

• Select VHDL files from \TestBuild\Design_A_CPU\Peripherals\UART folder

Add UART pins to top level entity pins list

entity TestIOP16B is
  port
  (
    -- Clock and Reset
    i_clk     : in std_logic := '1';		-- Clock (50 MHz)
    i_n_reset : in std_logic := '1';		-- SW2 on FPGA the card
    -- The key and LED on the FPGA card 
    i_key1    : in std_logic := '1';		-- SW1 on the FPGA card
    o_UsrLed  : out std_logic := '1';		-- USR LED on the FPGA card
		
    rxd1      : in std_logic := '1';		-- Hardware Handshake needed
    txd1      : out std_logic;
    cts1      : in std_logic := '1';
    rts1      : out std_logic;
    ...

Add to signals list

-- Decodes/Strobes
signal w_wrUart				:	std_logic;
signal w_rdUart				:	std_logic;
...
-- Interfaces
signal w_UartDataOut			:	std_logic_vector(7 downto 0);
...
-- Serial clock enable
signal serialEn      		: std_logic;		-- 16x baud rate clock

Add UART instance to section after begin

-- 6850 style UART
UART: entity work.bufferedUART
  port map (
    clk     			=> i_CLOCK_50,
    -- Strobes
    n_wr				=> not w_wrUart,
    n_rd    			=> not w_rdUart,
    -- CPU 
    regSel  			=> w_periphAdr(0),
    dataIn  			=> w_periphOut,
    dataOut 			=> w_UartDataOut,
    -- Clock strobes
    rxClkEn 			=> serialEn,
    txClkEn 			=> serialEn,
   -- Serial I/F
    rxd     			=> rxd1,
    txd     			=> txd1,
    n_rts   			=> rts1,
    n_cts   			=> cts1
  );

Add Baud Rate Generator instance

• Sets baud rate to 115,200 baud

-- Baud Rate Generator
-- These clock enables are asserted for one period of input clk, at 16x the baud rate.
-- Set baud rate in BAUD_RATE generic
BAUDRATEGEN	:	ENTITY work.BaudRate6850
  GENERIC map (
    BAUD_RATE	=> 115200
  )
  PORT map (
  i_CLOCK_50	=> i_clk,
  o_serialEn	=> serialEn
);

Add Chip selects logic

• Make sure to set the address of the UART (0x08-0x09 in this instance)

-- Strobes/Selects
w_wrUart <= '1' when ((w_periphAdr(7 downto 1)="0000100") and (w_periphWr = '1')) else '0';
w_rdUart <= '1' when ((w_periphAdr(7 downto 1)="0000100") and (w_periphRd = '1')) else '0';

Add UART output data to w_periphIn

• Make sure to set the address of the UART (0x08-0x09 in this instance)

-- Peripheral bus read mux
w_periphIn <=	"0000000"&w_keyBuff when w_periphAdr=x"00"							else
                w_timerOut          when w_periphAdr(7 downto 2) = "000001"	else
                w_UartDataOut       when w_periphAdr(7 downto 1) = "0000100"	else
                x"00";

• May have to fix some signal names
  • i_CLOCK_50 -> i_clk

Update Pins List

• New pins may need to be added

Verify no build issues

• Fix issues until it builds
• Test nothing broke
  • LED should blink

Create new peripherals

• Patterned like above example
• Takes in signals w_periphAdr, w_periphOut, w_periphWr, w_periphRd
• Create out signal and add to mux
• Create needed signals
• Create strobes

Write Assembly code

Add stack if needed

• If code will contain single level subroutine, fix cpu_001 calling instance

IOP16: ENTITY work.cpu_001
-- Need to pass down instruction RAM and stack sizes
  generic map 	( 
    INST_ROM_SIZE_PASS => 512, -- Small code size since program is "simple"
    STACK_DEPTH_PASS   => 1    -- Single level subroutine (not nested)
)

• If code will contain nested subroutines, fix cpu_001 calling instance

IOP16: ENTITY work.cpu_001
-- Need to pass down instruction RAM and stack sizes
  generic map 	( 
    INST_ROM_SIZE_PASS => 512, -- Small code size since program is "simple"
    STACK_DEPTH_PASS   => 4    -- Deeper stack
)

Edit example

• Start from existing code example \TestBuild\IOP16\IOP16_Code\testTimer folder
• Copy to \TestBuild\IOP16\IOP16_Code\UART_Loopback folder

• Open UART_Loopback.csv in spreadsheet program (LibreOffice CALC, Excel, etc)

LABEL	OPCODE	REG_LABEL	OFFSET_ADDR	COMMENT	V3.0.0
START	IOW	0X08	0X00	WRITE TO LED
	LRI	0X00	0X01	TIME 1 SEC
	IOW	0X00	0X06	STORE TO START TIMER
WAITDUN	IOR	0X01	0X04	READ TIMER
	ARI	0X01	0X01	CHECK BUSY
	BNZ	WAITDUN
	IOW	0X09	0X00	WRITE TO LED
	LRI	0X00	0X01	TIME 1 SEC
	IOW	0X00	0X06	STORE TO START TIMER
WAITD2	IOR	0X01	0X04	READ TIMER
	ARI	0X01	0X01	CHECK BUSY
	BNZ	WAITD2
	JMP	START

• Edit code
• Make sure to save as CSV

LABEL	OPCODE	REG_LABEL	OFFSET_ADDR	COMMENT	V3.0.0
START	JSR	INITURT		INITIALIZE THE ACIA UART
	LRI	0X03	0X01	LED INITIALLY OFF
	IOW	0X03	0X00	WRITE LED
WAITRXD	IOR	0X00	0X08	READ UART STATUS
	ARI	0X00	0X01	MASK RX DATA PRESENT BIT
	BEZ	WAITRXD		NO KBD DATA
	IOR	0X01	0X09	READ UART DATA TO REG1
WAITTXR	IOR	0X00	0X08	READ UART STATUS
	ARI	0X00	0X02	MASK TX EMPTY BIT
	BEZ	WAITTXR		TX NOT YET READY
	IOW	0X01	0X09	WRITE OUT DATA TO UART
	XRI	0X03	0X01	TOGGLE THE LED
	IOW	0X03	0X00	WRITE LED
	JMP	WAITRXD		RINSE AND REPEAT
INITURT	LRI	0X00	0X03	RESET UART COMMAND
	IOW	0X00	0X08	WRITE UART CMD REG
	LRI	0X00	0X20	TX CTRLS RTS
	IOW	0X00	0X08	WRITE UART CMD REG
	RTS

Assemble

• Use Assembler to create .MIF and .LST files
• Assembler is in \TestBuild\Design_A_CPU\Assembler folder
• If Python 3 is installed double click pyAssemble_cpu_001.py to run
• Browse to .\TestBuild\IOP16\IOP16_Code\UART_Loopback folder
• Select UART_Loopback.csv file
• Output .MIF and .LST files will be written to folder

Update .MIF file in ROM

• Update (as above)

• Set path to new code
• Make sure to set extension to .MIF

• Resources

Test the build

• Download code to FPGA
• Run puTTY
  • 115,200 baud
  • RTS/CTS handshake
• Type on keyboard
• Chars will loopback on serial
• LED will toggle on/off with each character

UART Loopback build

• Branches of the trees that capture these changes
  • IOP-16 UARTLoopback Tree
  • Design a CPU UARTLoopback Tree

Debug using SignalTap

• SignalTap is an embedded Logic Analyzer
  • Can be used to debug designs
• Right click on device Settings
• Select .stp file

• Select Tools, Signal Tap Logic Analyzer

• Add nodes

1. Compile
2. Download
3. Start capture
4. Press reset to trigger