usb_midi_host

USB MIDI Host

This project demonstrates the use of the STM32 USB Host Library by creating a MIDI Host. Plug in a MIDI device such as a musical keyboard or sequencer or controller. Playing notes or changing CCs will display on the console.

The board can provide VBus power (+5V) to the external device.

Modify main.cc to either select the OSD32MP1-BRK board or a Discovery board.

Since the OSD32MP1-BRK board is typically powered through the USB jack, you need to power the

When using the OSD32MP1-BRK board, you will need to power the board from the VIN and GND pins using a 5V supply, instead of powering it from the USB jack. This frees up the USB jack to use connect to a MIDI device. You probably will need to use a "USB OTG" (On The Go) adaptor that goes from micro-USB to female type-A, and then another cable that goes from male type-A to whatever your MIDI device has.

When using the STM32MP157C-DK2 Discovery board, power the board normally using the USB-C jack next to the SD-Card slot. The other USB-C jack can supply VBus to the MIDI device, but there is USB-C Interface IC (STUSB1600) responsible for enabling VBus. The example code configures this IC properly via I2C.

In this directory run:

make

To load the program onto your SD Card, follow the normal procedure (see here )

Power up and you should see this in the console:

USB MIDI Host test
Connect a USB cable to a MIDI device (keyboard, etc)
 
[waits here until you plug in a MIDI device]

USB Device Connected
USB Device Reset Completed
PID: 288h
VID: 1c75h
Address (#1) assigned.
Manufacturer : Arturia
Product : Arturia KeyStep 32
Serial Number : 00000000001A
Enumeration done.
This device has only 1 configuration.
Default configuration set.
DEBUG : Found Audio Control subclass

Switching to Interface (#1)
Class    : 1h
SubClass : 3h
Protocol : 0h
MIDI class started.
Class selected
Class active

[when you play on the MIDI device you'll see data like this:]
Note: 62 Vel: 108
Note: 62 off
Note: 57 Vel: 83
Note: 57 off
Note: 60 Vel: 79
Note: 60 off

The green LED will flash regularly to indicate the application is running, and the red LED will toggle whenever a MIDI message is received.

Dependencies and modifications

• STM32 USB Host Library v3.5.0 is used here, with one modication:

  • Core/Src/usbh_ctlreq.c: USBH_ParseCfgDesc() contains a bug that hangs when a MIDI Streaming device is connected. I patched this, and it's been reported to STM here

• STM32CubeH7 HAL drivers for usb are used here, with some modifications:

  • All files: "h7" changed to "mp1" (found in comments, #includes, include guards)

  • stm32mp1xx_hal_hcd.c/.h: no modifications

  • stm32mp1xx_ll_usb.c/.h: selectively took some modifications from the hftrx project:

    • Added constant USB_OTG_HS_EMBEDDED_PHY
    • Added a section in USB_CoreInit() to initialize global USB registers.
    • Commented out the name of a register that doesn't appear in the ST32MP157 CMSIS-device file (GDFIFOCFG)
    • In USB_DevInit(), initialize the Device Speed in the same way as with an OTG_ULPI_PHY
    • Altered logic in USB_EPStartXfer() for when to set the even/odd frame.
    • In USB_HostInit(), USB_HC_Init() and USB_HC_StartXfer(), don't use the CID register to determine if we're HS capable (always assume it's true)

  • stm32mp1xx_ll_usb_phy.c/.h: New files. These contain initialization code for the USBPHY peripheral. It's largely based on the implementation of such from the hftrx project.

• usbh_conf.c/.h: Copied from STM32CubeH7 example application USB Host Audio with these modifications:

  • Re-wrote HAL_HCD_MspInit/DeInit to use the MP1 registers. Turns on OTG and USBPHY clocks, and connects OTG to the port we use
  • Removed the use of a global HCD_HandleTypeDef. Instead we put it in MidiHost, so there's no issue if we ever need multiple MIDI Hosts
  • USBH_LL_Init(): does not init the HCD_Handle
  • Elsewhere we init the number of host channels to 16, and selected the right phy interface
  • Removed Board-specific stuff like VBUS enable driving
  • Fixed USBH_LL_Set/GetToggle not using the phost argument, but instead directly accessing the global handle

• usbh_midi.cc/hh: I started with the CDC Host Class from the STM USB Library and refactored it to match the MIDI USB specifications:

  • Renamed anything CDC to MIDI
  • Removed the code about line encoding.
  • Changed the class and subclass to AudioClass and MidiStreamingSubclass
  • Made the control interface descriptor optional, and selected the data interface.
  • Refactored for C++ (scoped enums, constexpr, function object callbacks)
  • Removed use of USBH_malloc/free, and instead let the application own/manager the host class instance handle (i.e. XXX_HandleTypeDef) and pass it to the host driver USBH_RegisterClass.
  • Refactored many common operations (like linking endpoints, opening pipes), moving them to a UsbHostHelper class
  • Refactored the callbacks so we can pass function objects like a lambda for the rx or tx callback.

Limitations, Bugs

Resources

ST has a good tutorial video playlist regarding USB and their library: MOOC STM32 USB training

The hftrx project is the only other example I found of USB working on baremetal STM32MP1. As noted above, many of the modifications necessary were already done here, and I copied many portions of code from here.