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midi-box-stm32

Midi Hub Device implementation (with 1 input and 3 output ports) example based on STM32F103 dev board.

Contains MIDI Device Class Middleware implementation for STM32 HAL USB drivers, compatible with STM32CubeMX/STM32CubeIDE code generator.
MIDI class V1.0 follows the "Universal Serial Bus Device Class Definition for MIDI Devices. Release 1.0 Nov 1, 1999"

User may specify number of physical/virtual input type MIDI_IN_PORTS_NUM ports and output type MIDI_OUT_PORTS_NUM ports.
The port means cable number or MIDI Jack associated with the endpoint that is transferring the data.
Right now up to 8 ports of each type supported, but only 12 ports in total.

Configuring user project with STM32CubeMX code generator to use MIDI Device Class Middleware

In STM32CubeMX / STM32CubeIDE:

• At USB -> enable Device FS
• At USB_DEVICE -> choose Human Interface Device Class (HID)
• (Optionally) At USB_DEVICE -> Device Descriptor -> update device descriptor information with your device info
• Generate code

To use MIDI Device Class middleware, project requires few modifications in generated code:

• Copy usbd_midi.c and usbd_midi.h to Middlewares/ST/STM32_USB_Device_Library/Class/MIDI/ Src and Inc folders respectively.
• In your IDE add those folders to C/C++ compiler include path, and files to corresponding group.
• Modify USB_DEVICE/App/usb_device.c:

#include "usbd_hid.h"  // replace this line
#include "usbd_midi.h" // with this line
...
if (USBD_RegisterClass(&hUsbDeviceFS, &USBD_HID) != USBD_OK)  // replace this line
if (USBD_RegisterClass(&hUsbDeviceFS, &USBD_MIDI) != USBD_OK) // with this line

• Modify USB_DEVICE/Target/usbd_conf.c:

#include "usbd_hid.h"  // replace this line
#include "usbd_midi.h" // with this line
...
/* USER CODE BEGIN EndPoint_Configuration_HID */ // this section may be absent if your device has no PMA, so no action required
HAL_PCDEx_PMAConfig((PCD_HandleTypeDef*)pdev->pData , 0x01 , PCD_SNG_BUF, 0xC0); // add this line
HAL_PCDEx_PMAConfig((PCD_HandleTypeDef*)pdev->pData , 0x81 , PCD_SNG_BUF, 0x100); // leave this line as is
/* USER CODE END EndPoint_Configuration_HID */
...
static uint32_t mem[(sizeof(USBD_HID_HandleTypeDef)/4)+1]; // replace this line
static uint32_t mem[(sizeof(USBD_MIDI_HandleTypeDef)/4)+1]; // with this line

• Modify Core/Inc/main.h:

/* USER CODE BEGIN EM */
#define MIDI_IN_PORTS_NUM   0x01 // Specify input ports number of your device
#define MIDI_OUT_PORTS_NUM  0x01 // Specify output ports number of your device

In some versions of the ST libraries you may face a MIDI_IN_PORTS_NUM macro is undeclared error. In this case you need to add MIDI_IN_PORTS_NUM and MIDI_OUT_PORTS_NUM definitions to the USB_DEVICE/Target/usbd_conf.h file.

Midi event packet structure:

|  4 bits  |  4 bits  |  4 bits  |  4 bits  |  8 bits  |  8 bits  |
|          |          |        MIDI_0       |  MIDI_1  |  MIDI_2  |
|   Cable  |   Code   |  Message |  Channel |  Byte 1  |  Byte 2  |

Please refer to USB-MIDI Event Packets in midi10.pdf for more info.

Send midi event packets report to host device:

• The size of reportBuffer should not exceed MIDI_EPIN_SIZE (64) bytes, and consist of a maximum of 16 event packets.
• Ensure that MIDI driver status is IDLE before each transfer initiation by:

USBD_MIDI_GetState(&hUsbDeviceFS) == MIDI_IDLE

• Send midi event packets with:

USBD_MIDI_SendReport(&hUsbDeviceFS, reportBuffer, eventPacketsNumber * 4);

Example sending one event packet to host device:

extern USBD_HandleTypeDef hUsbDeviceFS;
uint8_t reportBuffer[4] = {
  // cable - represents physical/virtual port number (0 - 15) of the device
  // code - in general cases is equal to midi message
  (cable << 4) | code,
  (message << 4) | channel,
  messageByte1,
  messageByte2,
};
...
while (USBD_MIDI_GetState(&hUsbDeviceFS) != MIDI_IDLE) {};
USBD_MIDI_SendReport(&hUsbDeviceFS, reportBuffer, 4);

Receive midi event packets from host device:

• Implement this weak function with something like this:

void USBD_MIDI_DataInHandler(uint8_t *usb_rx_buffer, uint8_t usb_rx_buffer_length)
{
  while (usb_rx_buffer_length && *usb_rx_buffer != 0x00)
  {
    cable = usb_rx_buffer[0] >> 4;
    code = usb_rx_buffer[0] & 0x0F;
    message = usb_rx_buffer[1] >> 4;
    channel = usb_rx_buffer[1] & 0x0F;
    messageByte1 = usb_rx_buffer[2];
    messageByte2 = usb_rx_buffer[3];
    usb_rx_buffer += 4;
    usb_rx_buffer_length -= 4;
  }
}