USBD_MIDI

Files: usbd_midi.h / usbd_midi.c
Directory: DAD_FORGE/Drivers/_MIDI
Description: Implementation of the USB MIDI Device class for STM32 with bidirectional bulk endpoints

📋 Class Description

The USBD_MIDI module is a complete implementation of the USB Audio/MIDI Device class according to the USB Audio 1.0 class driver from the STM32 USB Standard Device Library (USBD). It manages bidirectional bulk endpoints for transmitting and receiving MIDI messages via USB, with a complete configuration descriptor including jack descriptors for MIDI IN/OUT (embedded and external). The class interfaces with a callback handler (USBD_MIDI_ItfTypeDef) allowing the application to manage the physical transport of MIDI data.

🎯 Enumerations and Associated Structures

USBD_MIDI_HandleTypeDef

Main management structure for the USB MIDI Device class.

Element / Variable	Type / Value (if applicable)	Description
`buffer`	`uint8_t[64]`	Data buffer for MIDI messages (maximum size 64 bytes). Used for reception and transmission.
`rxLength`	`uint32_t`	Length of data currently received in the buffer. Indicates the number of valid bytes available.
`txState`	`uint8_t`	Transmission state (0 = ready, other values for intermediate states). Indicates if a transmission is in progress.
`rxState`	`uint8_t`	Reception state (0 = ready, other values for intermediate states). Indicates if reception is pending.

USBD_MIDI_ItfTypeDef

Structure containing interface callbacks for the user application.

Element / Variable	Type / Value (if applicable)	Description
`Init`	`int8_t (*)(void)`	Initialization callback: function called when the MIDI class is activated. Returns 0 on success, -1 on failure.
`DeInit`	`int8_t (*)(void)`	Deinitialization callback: function called when the MIDI class is deactivated. Returns 0 on success, -1 on failure.
`Receive`	`int8_t ()(uint8_t Buf, uint32_t Len)`	Reception callback: function called when MIDI data is available in the buffer. Returns the number of bytes read or -1 on error.

📚 Functions

USBD_MIDI_Init

Element	Details
Method	`static uint8_t USBD_MIDI_Init(USBD_HandleTypeDef *pdev, uint8_t cfgidx)`
Description	Initializes the USB MIDI Device class: allocates memory for the handle, opens IN/OUT bulk endpoints (0x81 and 0x01), configures transmission/reception state, and calls the `Init` callback of the user interface if registered. Prepares the OUT endpoint to receive the first packet.
Parameter(s)
`pdev`	Pointer to the USBD_HandleTypeDef structure of the USB device. Contains global information about the USB device state.
`cfgidx`	Configuration index (generally 1 for the first configuration). Indicates which USB configuration is active.
Return	Status code: `USBD_OK` (0) on success, `USBD_EMEM` on memory allocation failure, other USBD error codes depending on HAL/LL operation results.

USBD_MIDI_DeInit

Element	Details
Method	`static uint8_t USBD_MIDI_DeInit(USBD_HandleTypeDef *pdev, uint8_t cfgidx)`
Description	Deinitializes the USB MIDI Device class: closes IN/OUT bulk endpoints, calls the `DeInit` callback of the user interface to release physical resources, and frees the memory allocated for the handle. Resets endpoint usage flags to 0.
Parameter(s)
`pdev`	Pointer to the USBD_HandleTypeDef structure of the USB device.
`cfgidx`	Configuration index (generally 1).
Return	Status code: `USBD_OK` (0) on success, other error codes on failure.

USBD_MIDI_Setup

Element	Details
Method	`static uint8_t USBD_MIDI_Setup(USBD_HandleTypeDef pdev, USBD_SetupReqTypedef req)`
Description	Handles USB SETUP requests specific to the MIDI class. Currently does not implement class-specific requests (standard Audio MIDI classes typically do not require additional requests). Routes standard requests to the corresponding USBD handlers.
Parameter(s)
`pdev`	Pointer to the USBD_HandleTypeDef structure of the USB device.
`req`	Pointer to the USBD_SetupReqTypedef structure containing SETUP request details (type, request, value, index, data length).
Return	Status code: `USBD_OK` (0) on success, other error codes on failure.

USBD_MIDI_DataIn

Element	Details
Method	`static uint8_t USBD_MIDI_DataIn(USBD_HandleTypeDef *pdev, uint8_t epnum)`
Description	Callback called when the IN endpoint (0x81) is ready to transmit data. Prepares MIDI data from the buffer (`buffer`) for sending to the USB host. The effective transmission length is determined by `rxLength` or the buffer size depending on the current state.
Parameter(s)
`pdev`	Pointer to the USBD_HandleTypeDef structure of the USB device.
`epnum`	Endpoint number (1 for MIDI_IN_EP = 0x81).
Return	Status code: `USBD_OK` (0) on success, other error codes on data preparation failure.

USBD_MIDI_DataOut

Element	Details
Method	`static uint8_t USBD_MIDI_DataOut(USBD_HandleTypeDef *pdev, uint8_t epnum)`
Description	Callback called when the OUT endpoint (0x01) has received data from the USB host. Stores the data in the handle buffer and triggers the `Receive` callback of the user interface for application processing. Updates the reception state and prepares the next packet by calling `USBD_LL_PrepareReceive`.
Parameter(s)
`pdev`	Pointer to the USBD_HandleTypeDef structure of the USB device.
`epnum`	Endpoint number (1 for MIDI_OUT_EP = 0x01).
Return	Status code: `USBD_OK` (0) on success, other error codes on failure.

USBD_MIDI_GetFSCfgDesc

Element	Details
Method	`static uint8_t USBD_MIDI_GetFSCfgDesc(uint16_t length)`
Description	Returns the USB configuration descriptor for Full Speed (12 Mbps). The descriptor defines two interfaces: Interface 0 (Audio Control) and Interface 1 (MIDI Streaming with 2 bulk endpoints). Includes CS_INTERFACE descriptors for HEAD, MIDI_IN_JACK (embedded/external), and MIDI_OUT_JACK (embedded/external).
Parameter(s)
`length`	Pointer to a variable where the length of the returned descriptor will be stored. The descriptor is 101 bytes total.
Return	Pointer to the descriptor array: `USBD_MIDI_CfgFSDesc`.

📦 Data

Member	Type	Description
`pMidiItf`	`USBD_MIDI_ItfTypeDef *`	Pointer to the user callback structure registered via `USBD_MIDI_RegisterInterface()`. Allows calling Init/DeInit/Receive functions from the USB class.