Monday, July 15, 2013

PCF8574-based I2C LCD backpacks

So it seems that there's a lot of these about. A while back I picked up a bunch of cheap LCD backpacks on eBay, they look like this:

Like most of these cheap LCD backpack units, it utilises a GPIO expander chip. In this case, the chip used is a PCF8574. Most of the other I2C backpacks for Hitachi LCDs seem to utilise Microchip's MCP23008, which seems to be the little brother of the MCP23017 I've been playing with lately. So I had quite a hunt for some quick and easy code libraries to test out the backpacks with. I found one in Atlassian Bitbucket. I used version 1.2.1.

I then found this page which describes a number of the cheap eBay backpacks and clones. The third code example worked fine with the above library.

Unfortunately, after reducing the test sketch to merely the below, it was still gobbling 4768 bytes of flash. Unacceptably large, I think.

At some point in the past I'd picked up a bunch of black-on-green 16x2 LCDs for next to nothing. The total cost per LCD+backpack combo should come to easily less than $10 (AUD) each, including shipping. Pretty happy with that. They even work properly!

Friday, July 5, 2013

How I compile Stellaris projects under OSX

So I don't really know much about the TI Stellaris yet, having mainly used AVR chips to date. But I have a couple of the Stellaris Launchpads, and have managed to get the toolchain working under Mac OS X. I'm not going to repeat all the steps required for that here; you can use this page as a good starting point for that, and noting that you can save yourself a whole bunch of time/hassle by setting up MacPorts and doing this:

sudo port install arm-none-eabi-{gcc,binutils,gdb}

In my $HOME/Code/stellaris directory I have a single Makefile called Makefile.simple, and a separate subdirectory for each project. Its contents look like this:

CFLAGS_STELLARIS=-mthumb -mcpu=$(CPU) -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -ffunction-sections -fdata-sections -MD -I$(STELLARIS_TOP)
LDFLAGS_LEFT=-T $(PROG).ld --entry ResetISR 

$(PROG).bin: $(PROG).o startup_gcc.o $(PROG).ld
 $(LD) $(LDFLAGS_LEFT) -o $(PROG).bin $(PROG).o startup_gcc.o $(LDFLAGS_RIGHT)

$(PROG).out: $(PROG).bin
 $(OBJCOPY) -O binary $(PROG).bin $(PROG).out

 $(RM) $(PROG).bin $(PROG).out $(PROG).[od] startup_gcc.[od]

flash: $(PROG).out
 lm4flash $(PROG).out

You can see in the above that STELLARIS_TOP is set to the location in which I have unpacked (actually git clone...) StellarisWare. This is provided to gcc so that it can find C include files. Adjust as necessary if you are using my Makefile

In each project subdirectory I have a few files:

$ ls
Makefile       blinky.c       blinky.ld      startup_gcc.c

The Makefile merely includes ../Makefile.simple and specifies the name of this project:

-include ../Makefile.simple

The other files (blinky.ld and startup_gcc.c), at least at this learning stage, are the same for every project; I just copy them over from project to project.

To build my project, I just type make:

$ make
arm-none-eabi-gcc -std=c99 -Wall -Os -mthumb -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -ffunction-sections -fdata-sections -MD -I/Users/jslee/build/stellaris/stellaris   -c -o blinky.o blinky.c
arm-none-eabi-gcc -std=c99 -Wall -Os -mthumb -mcpu=cortex-m4 -mfpu=fpv4-sp-d16 -mfloat-abi=softfp -ffunction-sections -fdata-sections -MD -I/Users/jslee/build/stellaris/stellaris   -c -o startup_gcc.o startup_gcc.c
arm-none-eabi-ld -T blinky.ld --entry ResetISR  -o blinky.bin blinky.o startup_gcc.o --gc-sections

My project compiled and linked OK, so it is ready to send to the Launchpad with lm4flash:

$ make flash
arm-none-eabi-objcopy -O binary blinky.bin blinky.out
lm4flash blinky.out
ICDI version: 9270

Please let me know if you found this useful! I also use a similar Makefile structure for building and flashing AVR and MSP430 projects.

Sunday, June 30, 2013

MCP23017 and the Bus Pirate

So I wired up an MCP23017 GPIO expander to my Bus Pirate and couldn't understand why it wasn't acknowledging commands. Upon closer inspection of the datasheet I discovered that it expects an extra bit set in the I2C device address byte. The datasheet refers to this as the "Device Opcode".

Thus, if your device address lines are all tied to ground, ie. an address of 0x20, the address to write to is 0x40.

Once you've connected everything, the first step is to put your Bus Pirate in I2C mode and turn on the power:

Set speed:
 1. ~5KHz
 2. ~50KHz
 3. ~100KHz
 4. ~400KHz


This example assumes you've tied all three address lines from the MCP23017 to ground, making its I2C address 0x20. Now we'll configure both IO banks to be all outputs; the 0:3 notation tells the Bus Pirate to write the value three times. The first 0 selects the IODIRA register address. The second and third 0s clear all the bits in the IODIRA and IODIRB registers, thus configuring them as outputs.

WRITE: 0x40 ACK 
WRITE: 0x00 ACK 0x00 ACK 0x00 ACK 

Finally, we turn on all eight GPIOA pins by writing 0xFF to register 0x12.

WRITE: 0x40 ACK 
WRITE: 0x12 ACK 

As always, read the fine datasheet!

Quickstart guide: TI MSP430 on OSX Mountain Lion

I had all of this stuff working on my other OSX laptop but for some reason it wasn't as trivial to setup on my new laptop as it was last time around, mainly due to the USB driver. So I thought I'd save some notes for Google's (and possibly my!) future reference.

If this all fails on Mavericks when it arrives, I'll try to remember to update it.

  1. Install Xcode (I installed the commandline tools from inside Xcode too [Xcode menu => Preferences => Downloads tab]; these are probably not actually required)
  2. Install MacPorts
  3. Install the toolchain bits:
    sudo port install msp430-{binutils,gcc,gdb,libc}
  4. Get the fixed kernel extension source code - the TI download is broken under Mountain Lion and possibly Lion as well:
    git clone
  5. Follow the instructions included with the ez430rf2500 source to install the driver
  6. Plug in your Launchpad
  7. If everything is working, this should get you to an mspdebug shell: sudo mspdebug rf2500
[jslee@shamata Release] $ sudo mspdebug rf2500
MSPDebug version 0.21 - debugging tool for MSP430 MCUs
Copyright (C) 2009-2012 Daniel Beer 
This is free software; see the source for copying conditions.  There is NO

Trying to open interface 1 on 002
Initializing FET...
FET protocol version is 30066536
Set Vcc: 3000 mV
Configured for Spy-Bi-Wire
fet: FET returned error code 4 (Could not find device or device not supported)
fet: command C_IDENT1 failed
fet: identify failed
Trying again...
Initializing FET...
FET protocol version is 30066536
Set Vcc: 3000 mV
Configured for Spy-Bi-Wire
Sending reset...
Device ID: 0xf201
  Code start address: 0xf800
  Code size         : 2048 byte = 2 kb
  RAM  start address: 0x200
  RAM  end   address: 0x27f
  RAM  size         : 128 byte = 0 kb
Device: MSP430F2012/G2231
Number of breakpoints: 2
fet: FET returned NAK
warning: device does not support power profiling
Chip ID data: f2 01 01

Available commands:
    =           erase       isearch     opt         run         setwatch_w  
    alias       exit        load        power       save_raw    simio       
    break       fill        load_raw    prog        set         step        
    cgraph      gdb         locka       read        setbreak    sym         
    delbreak    help        md          regs        setwatch    verify      
    dis         hexout      mw          reset       setwatch_r  verify_raw  

Available options:
    color           gdb_loop        iradix          
    fet_block_size  gdbc_xfer_size  quiet           

Type "help " for more information.
Press Ctrl+D to quit.

(mspdebug) regs
    ( PC: 0ffff)  ( R4: 0dfde)  ( R8: 0fbef)  (R12: 0ffdf)  
    ( SP: 0ffff)  ( R5: 0f613)  ( R9: 07ffc)  (R13: 0feff)  
    ( SR: 00000)  ( R6: 0edff)  (R10: 0ffff)  (R14: 07bef)  
    ( R3: 00000)  ( R7: 0fbef)  (R11: 0cff7)  (R15: 0f5fc)  
    0ffff: ff                        

If all this works, you should be able to compile stuff and use mspdebug to load it into MSP430 flash via the Launchpad.

Friday, June 21, 2013

Van Halen @ Tokyo Superdome 2013-06-21 set list

  1. Unchained
  2. Runnin' with the devil
  3. She's the woman
  4. Show your love
  5. Tattoo
  6. Everybody wants some
  7. Somebody get me a doctor
  8. Downtown
  9. Hear about it later
  10. Pretty woman
  11. Drum & weird stuff
  12. You really got me
  13. Dance the night away
  14. ??? Synth song
  15. And the cradle will rock
  16. Hot for teacher
  17. Women in love
  18. Tora Tora???
  19. Mean streets
  20. Beautiful girls
  21. --- Dave lee Roth (as gaijin yakuza) short film
  22. DLR guitar acoustic intro to ice cream man
  23. Panama
  24. EVH solo thing
  25. Ain't talkin' 'bout love
  26. Encore: Jump