Sunday, April 29, 2012

WinUSB communication with STM32 (Part 3: Driver)

WinUSB driver must be linked to device. This means creating a driver INF file specifying WinUSB as driver for device with specific USB VID and PID. To complicate a bit further this information needs to be signed. That is done by signing a catalog file (CAT) created from INF file. Windows Driver Kit (WDK) includes all the tools to do it.
Driver (code) signing was introduced to help prevent the installation of software that is not trusted. From what I understand about driver signing is that Windows trust some global certificate authorities (CA). They then issue a code signing certificates containing the publishers' information to software publishers. By this they are saying that the publisher was verified by them. They do it manually like call the person/company which issued a request for certificate and verify their information. For this they charge a yearly fee. The result is a class 3 certificate which publisher uses to sign his software. On installation/execution Windows pop up a dialog asking if you trust the publisher named as specified in signature of the executable which you wish to install/run. Publisher can also send his driver directly to Microsoft for testing and signing. It is called WHQL Testing. I'm not sure but I think that drivers tested and signed by MS are installed without any warnings. Read more about it on wiki. And I believe this isn't free either.
Free of charge alternative is an open source code signing certificate issued by same trusted CA (e.g. The requirement is that "Open source" keywords are stated in certificate information (e.g. the Name field of certificate is "<publisher name>. Open Source Developer")
Another free of charge alternative for debugging is so called self-signed certificate. This is a certificate created by developer. I created a script that:
  1. creates the certificates,
  2. copies the redistributables from WDK,
  3. creates usbID.h file containing the IDs for USB descriptor which must match the INF file,  
  4. creates the INF file,
  5. checks the INF file,
  6. creates the CAT file from INF file and
  7. signs the CAT file with created certificate
I did this rather than publish a driver ready to install because it depends on personal information. Well I could distribute my self-signed certificate but I don't own a USB vendor ID. And since you have to have your own in the INF file the signed driver is no use to you because you must change it.

USB Vendor ID is another story to this. If you are serious and plan to sell USB devices you should apply for USB VID. It will be assigned to you after one time purchase. To additionally use the USB logo on the device you must pay a yearly fee... I think.

The script actually creates two certificates. First is your CA certificate. Second is code signing certificate issued by your CA. I omitted the installation of created CA certificate to "Root trusted certificates" because it seems to make no difference. First I thought that there will be no warnings if I put the created CA certificate next to other trusted CAs. But the Windows still pop up even more annoying warning saying that publisher can not be verified. I also tried generating the certificates with OpenSSL with no success.

Anyway, driver installation completes successfully if you choose to install anyway. The device is then displayed in the Device Manager as shown below.

Automatic installation can be done with dpinst.exe toll (part of WDK redistributables). But I didn't deal with why dpinst warning pops up saying that the publisher of dpinst is unknown. Maybe because it was ran from script?

To see details of all operations see the script.

This is the third post in this series (of total 4 posts). See 124.

[Update - I have a new WinUSB device project with STM32F407 without the need for Windows side driver info (.inf and .cat files) ]

Tuesday, April 24, 2012

WinUSB communication with STM32 (Part 2: Firmware)

The sources are available at Google code project.

I decided to make a communication pipes implementation as library so that it can be used with other USB hardware. The library uses two bulk endpoints and control endpoint. One bulk endpoint is for receiving the data and the other for sending the data. The default control endpoint (EP0) is used for communication control.
User's code should repeatedly call single function in library which does nothing while no data is received and calls user's function when new packet arrives.

Larger communication buffers are better for faster communication. To improve it even more the USB implementation should use double buffered endpoints - not the case at the moment.

This is the second post in this series (of total 4 posts). See 134

[Update - I have a new WinUSB device project with STM32F407 without the need for Windows side driver info (.inf and .cat files) ]

Wednesday, April 18, 2012

LPCXpresso upgrade for external debugger

I found long lost LPCXpresso under pile of paper when tidying the desk - you just have to do it every now and then :). Below are the images of modification for the board to work with external debugger. When added jumper is closed you can use external debugger with standard 10pin Cortex connector. If your debugger uses VCC pin (1) for target supply detection you should shorten the R29. My board came without R29 placed.

Added jumper holds integrated debugger in reset.

I soldered the pinhead on both sides for robustness.

Tuesday, April 17, 2012

WinUSB communication with STM32 (Part 1: Intro)

Aren't you fed up with putting a USB to serial converter in your embedded design while you have a USB capable device already in the design? Any other approach opens a can of worms though. Custom driver, certificate to sign it, USB vendor ID (2000$ at the moment), how to communicate with device on a layer above USB? But it is nice when OS pops up your name when your device is plugged in USB port. WinUSB is middle ground with tradeoffs one might consider.

I wanted to test the use of WinUSB with STM32F103 for some time now. When I finally got time I created a demo project. It shows basic request - response communication.
WinUSB kernel mode driver enables raw communication through USB pipes. In other words you can communicate with your USB device directly from application on the PC. So there is only code for application and code for firmware. Presuming you are not making standard USB class device like Mass Storage or HID. You might not even need custom PC side software in this case.
Furthermore the libraries to communicate are written for both ends to some extent. There SetupAPI and WinUSB on Windows side while ST has libraries for everything.
To get a taste check images below. I will post more about it in the future and probably publish the sources after I clean and organize them.

VS showing sent data.

winIDEA showing same received data on STM32.

This is the first post in this series (of total 4 posts). See  234.

[Update - I have a new WinUSB device project with STM32F407 without the need for Windows side driver info (.inf and .cat files) ]

Sunday, April 8, 2012

LCD Type On Cheap STM32 Camera Board From eBay

I bought a camera board with 2.8 inch TFT LCD and STM32 on eBay for 50 bucks some time ago. The primary project was put aside after I lost my initial excitement and motivation. After almost a year I was organizing libraries from ST for STM32 for some other purposes. I came across GUI library and remembered that I have the board laying around and decided to test the GUI library.

STM32 camera board (SWD debugging; I rewired the uSD  soon after I bought it)
Circle on functional LCD at the end (original FW displayed the picture from camera)
LCD connection - it is a 37pin connector

Soon I discovered that there are no usable markings for the LCD. I got the schematic from the seller and the demo project sources which were zipped in password protected archive. Nothing found with Google had any LCD type information. I had no way to determine how to set up the communication with the LCD. I didn't decide to query the seller for the password due to his lag in replying - I waited a week to get the mentioned files when I bought the board.
I assumed that the design is based on a evaluation board from ST. There are drives in ST libraries for the LCDs that ST uses on their boards.
Luckily I still have the original firmware (binary file only) to see how the LCD is used. I have programmed it and set up my debugger (winIDEA - I use iSystem emulator) to break on access to registers for the port to which LCD was connected. Fortunately only one port is used for LCD (PORTB). After each RUN the application stopped on each IO port signal change and I could read the signals values.

Watchpoint breakpoints setup in winIDEA
Port registers display in winIDEA

To automate the process of running, waiting to stop and reading the value I wrote a Python script. It uses the exposed API called "isystem.connect" for controlling/interfacing the winIDEA.
Obtained values exposed the LCD initialization sequence from the ST library for SPFD5408.

Ptyhon script:
import isystem.connect as ic
from isystem.connect import IConnectDebug as ICDebug

def toHEX8(val):
  return '0x{0:02X}'.format(val)

def toDEC(val):
  return '{0: 3d}'.format(val)

class LCDInterafceValues:
  def __init__(self): = 0
  def setNewValues(self, pinsValues): = pinsValues
  def isnCS(self):
    return ( & (1<<12)) != 0
  def isRS(self):
    return ( & (1<<13)) != 0
  def isnWR(self):
    return ( & (1<<14)) != 0
  def isnRD(self):
    return ( & (1<<15)) != 0
  def getnCS(self):
    if ( & (1<<12)) != 0: return 1
    else: return 0
  def getRS(self):
    if ( & (1<<13)) != 0: return 1
    else: return 0
  def getnWR(self):
    if ( & (1<<14)) != 0: return 1
    else: return 0
  def getnRD(self):
    if ( & (1<<15)) != 0: return 1
    else: return 0
  def getData(self):
    return & 0xFF
  def printHeader(self):
    print "CS  RS  RD  WR  data"
  def printLevels(self):
    if self.isnCS(): print "#  ",
    else: print "|  ",
    if self.isRS(): print "#  ",
    else: print "|  ",
    if self.isnRD(): print "#  ",
    else: print "|  ",
    if self.isnWR(): print "#  ",
    else: print "|  ",
    print toHEX8(self.getData()),
    print toDEC(self.getData())
cmgr = ic.ConnectionMgr()       # Create a connection manager
cmgr.connectMRU()               # Connect to the last used instance of winIDEA

debug = ic.CDebugFacade(cmgr)   # Create a debug object for the connected winIDEA 
debug.reset()                   # Reset CPU

pv = LCDInterafceValues()       # Create a value parser helper

# Watchpoints have already been set in dialogs in winIDEA
# Just run until a watchpoint is hit, then read the IO levels  
while True:                   # Run the CPU
  debug.waitUntilStopped()      # Do nothing while the CPU is running
  # Evaluate expression. Any C expression with firmware variables would be valid here.
  # '@' prefix tells winIDEA to evaluate (read from memory) a peripheral register.
  PortBPins = debug.evaluate(ICDebug.fMonitor , "@GPIOB_IDR").getInt()
  pv.setNewValues(PortBPins);   # Give the IO port value to helper
  pv.printLevels()              # Display values
Console output ( '#' means signal is HIGH and '|' that is LOW):
CS  RS  RD  WR  data
#   #   #   #   0x12  18
#   #   #   #   0x12  18
#   #   #   #   0x12  18
#   #   #   #   0x12  18
#   #   #   #   0x12  18
#   |   #   #   0x12  18
|   |   #   #   0x12  18
|   |   #   |   0x12  18
|   |   #   #   0x00   0
|   |   #   |   0x00   0
|   |   #   #   0xE3  227
#   |   #   #   0xE3  227
#   |   #   #   0xE3  227
#   #   #   #   0xE3  227
|   #   #   #   0xE3  227
|   #   #   |   0xE3  227
|   #   #   #   0x30  48
|   #   #   |   0x30  48
|   #   #   #   0x08   8
#   #   #   #   0x08   8
#   #   #   #   0x08   8
#   |   #   #   0x08   8
|   |   #   #   0x08   8
|   |   #   |   0x08   8
|   |   #   #   0x00   0
|   |   #   |   0x00   0
|   |   #   #   0xE7  231
#   |   #   #   0xE7  231
#   |   #   #   0xE7  231
#   #   #   #   0xE7  231
|   #   #   #   0xE7  231
|   #   #   |   0xE7  231
|   #   #   #   0x00   0
|   #   #   |   0x00   0
|   #   #   #   0x12  18
#   #   #   #   0x12  18
#   #   #   #   0x12  18
#   |   #   #   0x12  18
|   |   #   #   0x12  18
|   |   #   |   0x12  18
|   |   #   #   0x00   0
|   |   #   |   0x00   0
|   |   #   #   0xEF  239
#   |   #   #   0xEF  239
#   |   #   #   0xEF  239
#   #   #   #   0xEF  239
|   #   #   #   0xEF  239
|   #   #   |   0xEF  239
|   #   #   #   0x12  18
|   #   #   |   0x12  18
|   #   #   #   0x31  49
#   #   #   #   0x31  49
#   #   #   #   0x31  49