Category Archives: Software

DIY projects, MPPT Solar Charger, Software

USB Mass Storage Device Bootloader

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Let’s start with a video. It will tell you most of what I’m going to write about today.

That Hackaday Prize final has passed and unfortunately for me, the solar charger didn’t make it into the top 5. The good news is that there are plenty of projects and stuff that I would like to share. Things that I did over the last one or two years but never had time to write about. I’m trying to catch up with all that now.

First of all, I have completed the USB bootloader for the solar charger. This part of the project will enable the non-technical end user to easily and reliably update the firmware in the field.

Unlike a USB HID (Human Interface Device) bootloader that requires some application to run on the host computer, this USB MSD (Mass Storage Device) bootloader requires absolutely nothing in terms of host software. It’s entirely independent of the OS used. Windows, Linux, Mac, it all doesn’t matter. As long as they can deal with a USB drive, they’re good to go. Just copy the new software (in the form of an .hex file) to the Solar Charger drive and follow the instructions on the display.

It might even be that this bootloader is the world’s first of its kind for the PIC18 platform. To be sure, this kind of bootloader has been around for years for more powerful 32-bit microcontrollers like ARM Cortex and the like. But in my online research I have been unable to find any other such project for the PIC18 family (or any other 8-bit microcontroller). So I had no choice than to write my own. If you know of any other implementation, please let me know.

Once the file has been found and the user has pressed the button, the file is checked. If all those checks pass, we can be confident that we have a valid hex file. Of course, it doesn’t tell us anything about the quality of that code, that’s an other issue. But technically we should be fine.

Once the checks have passed, the user is once again requested to press the push button to confirm that this file should be programmed onto the chip. While it’s programming, it keeps displaying the current hex file entry it is processing to give the user an idea of the progress. It also keeps track of the number of flash pages it has written. One page corresponds to 1024 bytes on this architecture.

Once all the new code is flashed onto the chip, a message is displayed and the user is asked to once again press a key to re-boot the device into normal operating mode.

There are two different ways to enter bootloader mode. One is to press the push button at power-up. The other one consists in writing the value 0x94 (an arbitrarily chosen value) to the EEPROM address 0x100. In this case, the device will start up in bootloader mode no matter the state of the push button. The bootloader then overwrites this value (to 0x00) in order to start up normally next time.

After the reboot, you should be greeted by the startup screen of the solar charger firmware as shown above.

While I wrote this bootloader specifically for the solar charger, the code is rather universal. It can be ported to other PIC18 projects with relatively little effort. As always, the code’s on github: https://github.com/soldernerd/PIC18_USB_Bootloader.

Software

C# USB HID Utility

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Have you ever tried to write a program that connects to some device via USB? I have done so a few years ago and was shocked how much of a pain that is (at least on a Windows plattform). I always thought there should be a nice little library that wraps all those uggly DLL imports, marshalling and COM API calls and offers a nice and clean C# interface to the outside world.

Much to my surprise I found nothing that really did what I was looking for. Now I finally sat down and wrote my own. It’s on github.com under GNU GPLv3 license for anyone to modify and use.

My starting point was the Microchip PIC18F46J50 FS USB Demo Board. This nice little board comes pre-programmed as a HID (Human Interface Device) / MSD (Mass Storage Device) USB composite device and is a great starting point for anyone interested in building a USB device based on a PIC.

Once uppon a time, Microchip also wrote a WindowsForms application to showcase the USB functionality of their microcontrollers and that application (in various versions) can still be found here. It lets you read an analog voltage from the board, tells you if a pushbutton is pressed or not and lets you toggle an LED. Very simple but all you need to get started with your own device and application.

Unfortunately, that code no longer gets maintained and is quite outdated by now. It was created with VisualStudio2010 and .NET 2.0.  And all USB and WindowsForms code is mixed up in a single file which makes it difficult to re-use. It also lacks some functionality such as the ability to list available devices. Apart from that it works very well and stable so I used it as a starting point.

My solution is now based on VisualStudio Community 2015 (which is available for free) and .NET framework 4.6. So you can just download VisualStudio and open the HidUtilityDemo.sln file.

There are 3 projects inside the solution:

  • A WindowsForms application named HidDemoWindowsForms
  • A WPF application named HidDemoWpf
  • A console application named HidDemoConsole

All projects use a common file named hid.cs. This file is what this is all about. The applications mainly just show how to use it and give you a starting point for your own application.

hid.cs is not pretty. 900 something lines of DLL imports, COM object calls and marshalling. It’s C# but it doesn’t look and feel like C#. But it does all the heavy lifting for you and offers a nice, clean, truely C# interface for you to work with HID devices.

You add it to your namespace, create an instance of HidUtility, tell it what device to connect to  and subscribe to the events you are interested in:

// Get an instance of HidUtility
HidUtility HidUtil = new HidUtility();
// Connect to device with Vid=0x1234 and Pid=0x5678
HidUtil.SelectDevice(new hid.Device(0x1234, 0x5678));
// Subscribe to the events you care about
HidUtil.RaiseDeviceRemovedEvent += DeviceRemovedHandler;
HidUtil.RaiseDeviceAddedEvent += DeviceAddedHandler;
HidUtil.RaiseConnectionStatusChangedEvent += ConnectionStatusChangedHandler;
HidUtil.RaiseSendPacketEvent += SendPacketHandler;
HidUtil.RaisePacketSentEvent += PacketSentHandler;
HidUtil.RaiseReceivePacketEvent += ReceivePacketHandler;
HidUtil.RaisePacketReceivedEvent += PacketReceivedHandler;

You can also obtain a list of all available HID devices at any time:

foreach (Device dev in HidUtil.DeviceList)
{
Console.WriteLine(dev.ToString());
}

As the three projects demonstrate, the very same hid.cs file can be included in just about any C# project. There is not a single API call or anything in the remaining files.

Just register some event handlers and your application will be informed whenever a device has been added or removed, when a package of data has been received from the device, when the connection status has changed or whatever else.

So you don’t have to re-invent the wheel every time and can fully concentrate on the application you have in mind, not the details of USB communication.

A word of caution: I am by no means an expert C# programmer. I have tried the applications on 3 different PCs running Win7 and Win10, respectively. They seem to work reliably on any of these. Apart from that the code has not yet been productively deployed and there may well be some bugs and issues. If you find anything that doesn’t work, please let me know and I will do my best to get things fixed and updated on github. Also, please comment on this post if anything needs clarification.

So once again, the code is available for download from github.com/soldernerd/HID_Utility.