Commodore 64 for STM32F429 Discovery board

So here is a Commodore 64 emulator I built for STM32F429 Discovery board:

Yeah, the LCD is tiny at 2.4", and the emulation runs about 15% slower than an NTSC C64.  But it's running on a small embedded board that's available for under $30 US (DigiKey, Mouser, ...) including mounted LCD display and USB OTG jack.  Just add keyboard, OTG USB adapter, and power supply.

This is a port of my portable C64/6502 emulator for terminal console, which was a port of my Commodore/6502 emulator for Windows Console.   But this time, I dropped the console part, and went for real video (LCD) and USB keyboard support.   Hello PETSCII!

Keyboard mapping (showing my Dell keyboard):

   STOP(ESC) F1 F2 F3 F4 F5 F6 F7 F8            Restore(PrtScr/SysRq) Run/Stop(Pause/Break)

             1! 2@ 3# 4$ 5% 6^ 7& 8* 9( 0) -_ += Del/Ins(Back)    Ins Hme/Clr     / * -

   Ctrl(Tab) Q  W  E  R  T  Y  U  I  O  P  [  ]  £ (\)            Del           7 8 9 +

             A  S  D  F  G  H  J  K  L  ;: '" Return(ENTER)                     4 5 6

   LShift    Z  X  C  V  B  N  M  ,< .> /?  RShift                     Up       1 2 3

   C=(Ctrl)           SPACEBAR              C=(Ctrl)              Lft Down Rt   0 .   Enter

Features:

• 320x200 text screen on graphics LCD, with top/bottom border.
• USB Keyboard (e.g. PC-103) support (symbolic, not positional)
• Tab maps to C64 Ctrl key
• Ctlr maps to C64 Commodore key
• Esc key maps to C64 RUN/STOP key
• PrtScr/SysRq maps to C64 RESTORE key (supports STOP+RESTORE)
• PgUp also maps to C64 RESTORE key
• Full 6502 emulation.  Go ahead, run some machine language on it.
• Commodore character set
• Text video at $0400 (address 1024)
• Text color at $D800 (address 55296)
• Keyboard scan by writing to $DC00, reading from $DC01
• Full 64K RAM.  Update 2020-04-14: RAM/ROM/IO/Charset banking is implemented!  And 1K color nybbles
• 1/60 second IRQ.  So we've got the software clock: TI, TI$
• Upper/lower case switch ($D018), and reverse characters.
• Border color ($D020) and background color ($D021).

Limitations:

• Approximately 85% cpu speed of a real C64
• No NMI.  No Restore key.  Update 2020-04-15: implemented, see keyboard above.
• No other device support.  No tape, no disk, no serial, no cartridges, no joysticks, no printer.
• VIC-II support is limited to getting system booted.
• No full register support.
• Text address can't be moved.
• No graphics support.
• No programmable characters.
• No raster interrupts.
• No sprites.
• No left/right side border displayed.  Ran out of pixels.
• No CIA1/CIA2 (except for keyboard data ports, but no data direction registers)
• No SID.
• In progress.  There are bugs lurking (for example, the IRQ and USB keyboard stops working exactly at 35 minutes, 38 seconds from start, maybe a resource leak in third party libraries, so we'll call that time limited I guess)
• Keyboard support may need tweaks for more complete PETSCII key support
• No CAPS LOCK or SHIFT LOCK supported
• Doesn't utilize full capabilities of the STM32F429 MCU and discovery board components including 2.0MB of Flash (uses 110KB), 256KB of RAM (uses 83KB), 8MB SDRAM, motion sensor, user leds, user button, or other expansion capabilities.  Opportunity awaits!

Links:

• Source on mbed.com (utilizes MBED OS, MBED USBHOST, ST429 BSP)
• Terminal Console related C64/6502 emulator source on github.com
• Binary firmware (yes you can flash and try right now if you have the hardware)
• ST-Link Utility (flash utility for STM32, programmer built into discovery board)
• STM32F429x Datasheet
• STM32F429IDISCOVERY resources at st.com

Credit:  

• Something similar has been done before (but not source related).  See hackaday.com.
• Thanks to STMicroelectronics for the cool development board!

Getting started with OpenOCD

As referenced in my JTAG Adapter post the OpenOCD project is an open source JTAG program and set of drivers.  Professional JTAG programmers can commonly cost US $100 and up (some are thousands), and are often proprietary to a specific development toolset.  Open source and open hardware efforts have made JTAG available at much lower cost and at least works with open source development toolsets such as gcc/gdb and Eclipse, as well as some commercial offerings that are built on Eclipse.

Olimex has collected these open source development toolsets with OpenOCD and created a single installer called Olimex OpenOCD Development Suite for use with their development boards and their JTAG programmer.   Installing their suite is one of the easiest ways to get an ARM gcc toolchain installed on your system with an IDE and JTAG programmer.  Their toolset includes OpenOCD, Eclipse, gcc/gdb, and Zylin Embedded CDT.  Sample projects are provided for some of their Atmel, STM32, and NXP (LPC) boards.  I found that I needed to perform slight revisions their OpenOCD scripts included in at least the SAM7-P256-cdc_FLASH project because they were out of date.  Once that was done, I was using my JTAG adapter with their ARM7 board performing programming and debugging.  This suite and examples can be leveraged to target other boards. 

OpenOCD can also be used directly from the command line to make a connection with a board, and then use telnet to issue commands (see User's Guide) to direct it.  From the command line you can verify and discover commands to issue to your board.  In the following examples I will use my JTAG programmer to talk to the STM32F4Discovery board.  I have a breakout board for this development board that includes a JTAG socket.  I have disconnected the jumpers on the STM32F4Discovery for its onboard ST-LINK/V2 debugger, so I can use my JTAG programmer instead.

First you must have an interface script to talk to your JTAG programmer.  From the openocd-0.6.1 directory, I copied scripts/interface/ftdi/flossjtag.cfg to the file ft2232h.cfg in the current directory.  Then I commented out the ftdi_device_desc statement in that file, and appended
    adapter_khz 500
to the end of the file.

$ bin/openocd-0.6.1.exe -f ft2232h.cfg -f scripts/target/stm32f4x.cfg

Open On-Chip Debugger 0.6.1 (2012-10-07-10:34)
Licensed under GNU GPL v2
For bug reports, read    http://openocd.sourceforge.net/doc/doxygen/bugs.html
WARNING!
This file was not tested with real interface, it is based on code in ft2232.c.
Please report your experience with this file to openocd-devel mailing list,
so it could be marked as working or fixed.
Info : only one transport option; autoselect 'jtag'
adapter speed: 500 kHz
adapter speed: 1000 kHz
adapter_nsrst_delay: 100
jtag_ntrst_delay: 100
cortex_m3 reset_config sysresetreq
Info : clock speed 1000 kHz
Info : JTAG tap: stm32f4x.cpu tap/device found: 0x4ba00477 (mfg: 0x23b, part: 0xba00, ver: 0x4)
Info : JTAG tap: stm32f4x.bs tap/device found: 0x06413041 (mfg: 0x020, part: 0x6413, ver: 0x0)
Info : stm32f4x.cpu: hardware has 6 breakpoints, 4 watchpoints

Then I open a telnet window to localhost port 4444.  From here I can issue various commands to OpenOCD to perform JTAG commands.

$ telnet localhost 4444

Open On-Chip Debugger
> reset halt
JTAG tap: stm32f4x.cpu tap/device found: 0x4ba00477 (mfg: 0x23b, part: 0xba00, ver: 0x4)
JTAG tap: stm32f4x.bs tap/device found: 0x06413041 (mfg: 0x020, part: 0x6413, ver: 0x0)
target state: halted
target halted due to debug-request, current mode: Thread
xPSR: 0x01000000 pc: 0xfffffffe msp: 0xfffffffc
> flash probe 0
device id = 0x10016413
flash size = 1024kbytes
device id = 0x10016413
flash size = 1024kbytes
flash 'stm32f2x' found at 0x08000000
> flash banks
#0 : stm32f4x.flash (stm32f2x) at 0x08000000, size 0x00100000, buswidth 0, chipwidth 0
> flash list
{name stm32f2x base 134217728 size 1048576 bus_width 0 chip_width 0}
> flash erase_check 0
successfully checked erase state
        #  0: 0x00000000 (0x4000 16kB) erased
        #  1: 0x00004000 (0x4000 16kB) erased
        #  2: 0x00008000 (0x4000 16kB) erased
        #  3: 0x0000c000 (0x4000 16kB) erased
        #  4: 0x00010000 (0x10000 64kB) erased
        #  5: 0x00020000 (0x20000 128kB) erased
        #  6: 0x00040000 (0x20000 128kB) erased
        #  7: 0x00060000 (0x20000 128kB) erased
        #  8: 0x00080000 (0x20000 128kB) erased
        #  9: 0x000a0000 (0x20000 128kB) erased
        # 10: 0x000c0000 (0x20000 128kB) erased
        # 11: 0x000e0000 (0x20000 128kB) erased
> dump_image image.bin 0x08000000 0x100000
dumped 1048576 bytes in 14.406221s (71.080 KiB/s)
> flash write_image erase stm32f4discovery_00.s19
auto erase enabled
wrote 1048576 bytes from file stm32f4discovery_00.s19 in 31.499985s (32.508 KiB/s)
> reset run
JTAG tap: stm32f4x.cpu tap/device found: 0x4ba00477 (mfg: 0x23b, part: 0xba00, ver: 0x4)
JTAG tap: stm32f4x.bs tap/device found: 0x06413041 (mfg: 0x020, part: 0x6413, ver: 0x0)
> exit


^C

There you have it, some example OpenOCD commands.  Hope you learned something useful.

OpenOCD FT2232H based JTAG Adapter(s) with UART

USB to JTAG, and JTAG to JTAG adapters

JTAG adapters are commonly used to program and debug microcontrollers and microprocessors.  This circuit is a prototype of one that is compatible with OpenOCD which is an open source JTAG program and set of drivers.  The board and circuit presented here is simply a set of connections, jumpers, and sockets that leverage the FT2232H Mini Module as a USB to JTAG adapter. 

Four JTAG and/or SWD ports are provided for compatibility with a variety of development boards: 6-pin ST-LINK, 8-pin LPC-Link, 10-pin JTAG, 20-pin JTAG. 

Using one of two plug in modules, the 10-pin is either 0.05" pitch or 0.1" pitch. I plan to include both 10-pin formats on any revisions to this JTAG board so I can easily adapt between the formats.

When used as a USB JTAG adapter, only one of the JTAG or SWD ports is used.  Note that pin 1 is consistently in the upper left on this board.  Ribbon cables or socket cables are used to connect to the target board.  It is useful to have sets of cables that support all these pin-out formats.  Cables are quicker and easier than single conductor jumpers between individual connector pins.

An alternate use is to adapt from one pin-out to another when using other JTAG and/or SWD programmers.  In this case the mini module can be removed or simply disconnect the USB cable from the computer.  The board is only being used to convert pin-outs.  For example, I can use a 6-conductor socket to socket cable to connect the ST-LINK port to the ST-LINK socket on my STM32F4Discovery board, and then connect the LPC-Link socket via an appropriate cable to an LPCxpresso board.  I have used this method to program and debug my LPCxpresso board for LPC1343 with CooCox IDE.

Multiple JTAG adaptions are possible

• ST-LINK to LPC-Link
• ST-LINK to 10-pin
• ST-LINK to 20-pin
• LPC-Link to 10-pin
• LPC-Link to 20-pin
• 10-pin to 20-pin
• 10-pin (1.27mm) to 10-pin (2.54mm) in future revision

Boards I was able to communicate with either with OpenOCD, ST-LINK, or CoLinkEx using the JTAG adapter(s) board include:

• Netduino Shield Base Beta (STM32F205RE)
• Netduino Plus 2 (STM32F405RG)
• Arduino Due (ATSAM3X8E/AU)
• Simplecortex (LPC1769)
• STM32F4Discovery (STM32F407VG)
• CooCox Embedded Pi (STM32F103RB)
• NGX LPC1830-Xplorer
• Olimex SAM7-P256 (AT91SAM7S256)
• LPCxpresso for LPC1343

Caveats and Warnings.  Note that I did not do extensive testing.  I am not sure the RESET and RTCK lines are working.  Some boards I could only connect to using SWD instead of JTAG.  Driver installation and basic use of OpenOCD is not described in this post, so see Getting Started with OpenOCD.

Inspiration and References.  Most of the JTAG circuit is gleaned from multiple FTDI specifications regarding the FT2232H, Mini Module, and related MPSSE Basics Application Note AN_135.  And the circuit is very similar to the FLOSS-JTAG one shown here.



Under belly of the JTAG board

 


JTAG Schematic

Hello World tutorial for STM32 Discovery boards using CooCox CoIDE and GCC ARM

ST Microelectronics has been supporting their Discovery line of ARM demonstration and development boards for a while now.  I was first introduced to the STM32 Value line discovery (STM32-F1), getting a free one at one of the embedded development conferences in San Jose or Santa Clara.  I had tucked it away for safe keeping (or hoarding), and over the years also acquired a STM32-F0, STM32-F4, and STM32-F3.  These are low cost (most $8-$11, with one at $15 US), and some of the more advanced boards include an accelerometer, gyroscope, or compass and multiple LEDs.

I recently stumbled across the CooCox CoIDE for working with the Simplecortex (I'll blog more about NXP chips and boards another time), and while starting to play with it, discovered that this IDE also supported the STM32 boards.  Which is great, as I had just started reading Discovering the STM32 Microcontroller by Geoffrey Brown of Indiana University and wanted to try my hand at developing for ARM in C.

As stated in their tagline, CooCox is a set of "Free and Open ARM Cortex MCU Development Tools."  CoIDE is an Eclipse based integrated development enviroment supporting the standard GCC ARM tool set: compiler, assembler, linker, and debugger.  The STM32 discovery boards include an embedded ST-LINK or ST-LINK/V2 which is supported by CoIDE for flashing and debugging.  The real value add by CoIDE is point and click choice of MCU library modules for various peripherals, with hypertext library references and examples.  CooCox supports a variety of ARM Cortex MCUs from various manufacturers.  ST is just one of the manufacturers.

Here I will show you how to install CoIDE and essential dependencies to develop a simple Hello World program for the STM32 Value line discovery board.  The steps are very similar for the other boards (except STM32-F3 is not directly supported at this time).  The program will display debug output from printf() through the ST-LINK to the IDE's console window.  This is the essential first program to see results from a program running on an embedded board.  And it's not just a blinking LED, though we'll do that too.

One time installation and configuration.

1. Download ARM GCC
2. Download CoIDE
3. Download STM32 ST-LINK Utility
3. Install ARM GCC
4. Install CoIDE
5. Configure CoIDE to point to ARM GCC
6. Install STM32 ST-LINK Utility
7. Plug in USB cable from PC to ST-LINK on discovery board

Creating your first project.

1. Click Create Project, name it hello
2. When prompted Chip or Board, choose Chip
3. Choose ST, and STM32F100RB.  Click Finish
4. In the Repository window, click on Semihosting and GPIO.  Required dependencies will autoselect
5. Double click on main.c in the Project window, and modify to contain

#include <stdio.h>
#include <stm32f10x_gpio.h>
#include <stm32f10x_rcc.h>

int main(void)
{
 GPIO_InitTypeDef gpio;
 RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOC, ENABLE);

 GPIO_StructInit(&gpio);
 gpio.GPIO_Pin = GPIO_Pin_9; // Green LED
 gpio.GPIO_Mode = GPIO_Mode_Out_PP;
 gpio.GPIO_Speed = GPIO_Speed_2MHz;
 GPIO_Init(GPIOC, &gpio);

 gpio.GPIO_Pin = GPIO_Pin_8; // Blue LED
 GPIO_Init(GPIOC, &gpio);

 printf("Hello World!\r\n");

 while(1)
 {
  static int count=0;
  static int i;
  static int led_state=0;

  for (i=0; i<1000000; ++i);
  GPIO_WriteBit(GPIOC, GPIO_Pin_9, led_state ? Bit_SET : Bit_RESET);
     led_state = !led_state;
     GPIO_WriteBit(GPIOC, GPIO_Pin_8, led_state ? Bit_SET : Bit_RESET);

  printf("%d\r\n", ++count);
 }
}

6. Open printf.c from the Project window
7. Add #include <semihosting.h> after the other includes.
8. In the PrintChar method, add the following line before the closing brace

SH_SendChar(c);

 

9. Right click on hello in tree of Project Window and choose Configuration

10. Navigate to Debugger tab, and verify ST-Link is chosen

11. Click on Semihosting Enable

12. Choose Project + Build, should be successful

13. Choose Debug + Debug, will deploy to board and stop at top of main

14. Choose Debug + Run to continue the program, should see output in Semihosting window