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midi2usbhost C Code Software

This project depends on the usb_midi_host, midi_uart_lib, and ring_buffer_lib projects. They are included as git submodules.

This project also uses the the Raspberry Pi Pico SDK and it uses the TinyUSB library for the USB stack. At the time of this writing, the version of the TinyUSB library that ships with the pico-sdk version 1.5.1 is not able to use application USB Host drivers like usb_midi_host. You will need a version of TinyUSB from 15-Aug-2023 or later that calls usbh_app_driver_get_cb() to install application USB Host drivers. See below for instructions on how to update the TinyUSB library.

Setting Up Your Build and Debug Environment

I am running Ubuntu Linux 22.04LTS on an old PC. I have Visual Studio Code (VS Code) installed and went through the tutorial in Chapter 7 of Getting started with Raspberry Pi Pico to make sure it was working first. I use a picoprobe for debugging, so I have openocd running in a terminal window. I use minicom for the serial port terminal (make sure your linux account is in the dialup group).

Updating the TinyUSB library

The Pico SDK uses the main repository for TinyUSB as a git submodule. Earlier revisions of this project replaced the TinyUSB library with a forked version. This is no longer necessary. You will need to check the version of TinyUSB you are using and update it to a more recent version if it is older than 15-Aug-2023.

Assuming your pico-sdk is installed in ${PICO_SDK_PATH}, then follow these steps to force your version of TinyUSB to the latest version. The git remote command is only required if you previously changed it per the instructions in older revisions of this project.

git remote set-url origin https://github.com/hathach/tinyusb.git
cd ${PICO_SDK_PATH}/lib/tinyusb
git checkout master
git pull

Get the project code

Clone the midiusb2host project to a directory at the same level as the pico-sdk directory.

cd ${PICO_SDK_PATH}/..
git clone --recurse-submodules https://github.com/rppicomidi/midi2usbhost.git

Command Line Build (skip if you want to use Visual Studio Code)

Enter this series of commands (assumes you installed the pico-sdk and the midid2usbhost project in the $HOME/foo directory)

export PICO_SDK_PATH=$HOME/foo/pico-sdk/
cd $HOME/foo/midi2usbhost/C-Code
mkdir build
cd build
cmake ..
make

The build should complete with no errors. The build output is in the build directory you created in the steps above.

Set up and launch Visual Studio Code

Enter this series of commands

cd midiusb2host/C-Code
mkdir build
cd build
touch compile_commands.json

Run these once in a terminal before you launch VS Code. The first sets up the environment and the second launches openOCD for use with the picoprobe

export PICO_SDK_PATH=$HOME/projects/pico/pico-sdk/
gnome-terminal -- openocd -f interface/cmsis-dap.cfg -c "adapter speed 5000" -f target/rp2040.cfg -s tcl
gnome-terminal -- minicom -D /dev/ttyACM0 -b 115200

Finally, launch VS Code

code

Load the project

The first time you run the project, in VS Code, File->Open Folder... and select the midiusb2host/C-Code folder. Click OK.

You will be prompted to set up the Kit. Choose GCC for arm-none-eabi [your version]

Run the code

In VS Code, select Run->Start Debugging from the Run menu. The first time, you will be prompted to select the launch target. Select midi2usbhost.

VS Code debugger will load the code to your target Pico board and halt at main(). Press the triangular run icon to start it running. If all goes well, you should see the LED on your Pico board blinking off and on once per second and your should see the following in your minicom terminal window:

Pico MIDI Host to MIDI UART Adapter
Configured MIDI UART 1 for 31250 baud

Hardware Variations

If you are targeting a board other than the Raspberry Pi Pico that does not have UART 1 available or does not have GPIO 4 or GPIO 5, which are the default pins for, you can data to CMake to properly target your hardware. There are 3 variables you can to set

  • MIDI_UART_NUM can be 0 or 1 to depending on whether you use uart0 or uart1 for MIDI. The default value is 1.
  • MIDI_UART_TX_GPIO is the GPIO number (not the package pin number) of the UART's transmit pin. The default is 4. If you choose a different pin, make sure that the UART you are using as set by MIDI_UART_NUM can use that pin for the UART TX function.
  • MIDI_UART_RX_GPIO is the GPIO number (not the package pin number) of the UART's receiver pin. The default is 5. If you choose a different pin, make sure that the UART you are using as set by MIDI_UART_NUM can use that pin for the UART RX function.

You can change these values by setting them as environment variables and then running cmake or you can pass them directly on the cmake command line using the -D option. For example, to use UART 0 on GPIO 12 & 13 as the MIDI UART you can build your code this way:

cd build
cmake -DMIDI_UART_NUM=0 -DMIDI_UART_TX_GPIO=12 -DDMIDI_UART_RX_GPIO=13 ..
make

or this way:

export MIDI_UART_NUM=0
export MIDI_UART_TX_GPIO=12
export MIDI_UART_RX_GPIO=13
cmake ..
make

I find the latter method simpler when I am using the VS Code workflow to build the code.

Troubleshooting

If your project works for some USB MIDI devices and not others, one thing to check is the size of buffer to hold USB descriptors and other data used for USB enumeration. Look in the file tusb_config.h for

#define CFG_TUH_ENUMERATION_BUFSIZE 512

Very complex MIDI devices or USB Audio+MIDI devices like DSP guitar pedals or MIDI workstation keyboards may have large USB configuration descriptors. This project assumes 512 bytes is enough, but it may not be for your device.

To check if the descriptor size is the issue, use your development computer to dump the USB descriptor for your device and then add up the wTotalLength field values for each configuration in the descriptor.

For Linux and MacOS Homebrew, the command is lsusb -d [vid]:[pid] -v For Windows, it is simplest to install a program like Thesycon USB Descriptor Dumper.

For example, this is the important information from lsusb -d 0944:0117 -v from a Korg nanoKONTROL2:

  bNumConfigurations      1
  Configuration Descriptor:
    bLength                 9
    bDescriptorType         2
    wTotalLength       0x0053
    bNumInterfaces          1
    bConfigurationValue     1
    iConfiguration          0 
    bmAttributes         0x80
      (Bus Powered)
    MaxPower              100mA

This is the important information from the Thesycon USB Descriptor Dumper for a Valeton NUX MG-400

0x01	bNumConfigurations

Device Qualifier Descriptor is not available. Error code: 0x0000001F


-------------------------
Configuration Descriptor:
-------------------------
0x09	bLength
0x02	bDescriptorType
0x0158	wTotalLength   (344 bytes)
0x04	bNumInterfaces
0x01	bConfigurationValue
0x00	iConfiguration
0xC0	bmAttributes   (Self-powered Device)
0x00	bMaxPower      (0 mA)

You can see that if CFG_TUH_ENUMERATION_BUFSIZE were 256 instead of 512, the Korg nanoKONTROL2 would have no trouble enumerating but the Valeton NUX MG-400 would fail because TinyUSB couldn't load the whole configuration descriptor to memory.