GigaDevice Semiconductor GD32 Series User manual

GigaDevice Semiconductor Inc.
GD32 USBFS&USBHS
Firmware Library User Guide
Application Note
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Table of Contents
Table of Contents...........................................................................................................2
List of Figures ................................................................................................................4
List of Tables ..................................................................................................................5
1. Introduction...........................................................................................................7
2. Library architecture and file structure ................................................................8
2.1. Library Architecture .................................................................................................... 8
2.2. File structure................................................................................................................ 9
3. USBFS bottom driver .........................................................................................12
4. USBFS middle layer driver.................................................................................13
4.1. Host middle layer driver function............................................................................. 13
4.2. Device middle layer driver function ......................................................................... 15
5. USBFS Device Library........................................................................................18
5.1. Device Library Configuration.................................................................................... 18
5.1.1. usbd_conf.h .......................................................................................................................... 18
5.1.2. usb_conf.h ............................................................................................................................ 18
5.2. Firmware library process .......................................................................................... 19
5.3. Descriptor .................................................................................................................. 20
5.4. Interrupt handling...................................................................................................... 22
5.5. USB Device Class Interface ...................................................................................... 26
5.6. Data transmission process ....................................................................................... 28
5.6.1. IN direction............................................................................................................................ 28
5.6.2. OUT direction........................................................................................................................ 28
5.7. USB device class routine .......................................................................................... 29
5.7.1. AUDIO................................................................................................................................... 29
5.7.2. CDC ...................................................................................................................................... 33
5.7.3. DFU....................................................................................................................................... 36
5.7.4. MSC ...................................................................................................................................... 42
5.7.5. HID........................................................................................................................................ 45
5.7.6. USB printer ........................................................................................................................... 47
6. USBFS Host Library ...........................................................................................49
6.1. Host Library Configuration ....................................................................................... 49
6.1.1. usbh_conf.h .......................................................................................................................... 49

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6.1.2. usb_conf.h ............................................................................................................................ 49
6.2. Host VBUS Configuration ......................................................................................... 50
6.3. Interrupt handling...................................................................................................... 52
6.4. State Machine Process.............................................................................................. 56
6.5. USB Host Library User Interface .............................................................................. 56
6.6. USB Host Library Device Class Interface ................................................................ 58
6.6.1. HID device class ................................................................................................................... 58
6.6.2. MSC device class ................................................................................................................. 60
6.7. USB Host Library Routine......................................................................................... 61
6.7.1. HID HOST............................................................................................................................. 61
6.7.2. MSC HOST ........................................................................................................................... 62
7. Revision history..................................................................................................64

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List of Figures
Figure 2-1. GD32 USBFS firmware library framework...................................................................... 8
Figure 2-2. USBFS Firmware Library Folder ..................................................................................... 9
Figure 2-3. Device folder ..................................................................................................................... 9
Figure 2-4. Driver folder .................................................................................................................... 10
Figure 2-5. Host folder....................................................................................................................... 10
Figure 2-6. Ustd folder........................................................................................................................11
Figure 5-1. Firmware library flowchart............................................................................................. 20
Figure 5-2. Device class file path ..................................................................................................... 21
Figure 5-3. Device class file.............................................................................................................. 27
Figure 5-4. AUDIO macro configuration .......................................................................................... 29
Figure 5-5. AUDIO device class ........................................................................................................ 31
Figure 5-6. Audio playback file......................................................................................................... 32
Figure 5-7. Audio system sound configuration .............................................................................. 33
Figure 5-8. Audio recording listening configuration...................................................................... 33
Figure 5-9. CDC device class............................................................................................................ 35
Figure 5-10. Virtual serial data transmitting and receiving ........................................................... 36
Figure 5-11. Virtual serial port large data transmitting and receiving.......................................... 36
Figure 5-12. DFU state machine flow chart ..................................................................................... 37
Figure 5-13. DFU device class .......................................................................................................... 39
Figure 5-14. All in one connection ................................................................................................... 40
Figure 5-15. All in one uploading ..................................................................................................... 41
Figure 5-16. All in one Option Byte operation................................................................................. 41
Figure 5-17. MSC device class.......................................................................................................... 44
Figure 5-18. MSC device formatting................................................................................................. 44
Figure 5-19. MSC device read-write test.......................................................................................... 44
Figure 5-20. HID device class ........................................................................................................... 46
Figure 5-21. printer device class ...................................................................................................... 48
Figure 6-1. Construct circuit through triode to control VBUS ...................................................... 51
Figure 6-2. Control VBUS by Logic Chip Circuit............................................................................. 52
Figure 6-3. USB host state machine ................................................................................................ 56
Figure 6-4. Host device class interface file path............................................................................. 58
Figure 6-5. Hid host routine operation diagram.............................................................................. 62
Figure 6-6. Routine for mouse-over display of HID host ............................................................... 62
Figure 6-7. Routine for HID host keyboard display ........................................................................ 62
Figure 6-8. MSC host routine operation steps................................................................................ 63
Figure 6-9. MSC host routine display .............................................................................................. 63

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List of Tables
Table 1-1. Applicable products ........................................................................................................... 7
Table 3-1. USBFS underlying file...................................................................................................... 12
Table 3-2. usb_core.h/.c file function............................................................................................... 12
Table 4-1. USBFS middle layer driver file........................................................................................ 13
Table 4-2. drv_usb_host.h/.c file function ....................................................................................... 13
Table 4-3. drv_usbh_int.h/.c file function ........................................................................................ 13
Table 4-4. usbh_core.h/.c file function ............................................................................................ 14
Table 4-5. usbh_enum.h/.c file function .......................................................................................... 14
Table 4-6. usbh_pipe.h/.c file function............................................................................................. 14
Table 4-7. usbh_transc.h/.c file function ......................................................................................... 15
Table 4-8. drv_usb_dev.h/.c file function......................................................................................... 15
Table 4-9. drv_usbd_int.h/.c file function ........................................................................................ 16
Table 4-10. usbd_core.h/.c file function .......................................................................................... 16
Table 4-11. usbd_enum.h/.c file function ........................................................................................ 16
Table 4-12. usbd_transc.h/.c file function ....................................................................................... 17
Table 5-1. usbd_conf.h configuration description ......................................................................... 18
Table 5-2. usb_conf.h configuration description............................................................................ 19
Table 5-3. USBFS device interruption.............................................................................................. 22
Table 5-4. AUDIO relevant descriptors ............................................................................................ 29
Table 5-5. AUDIO device class interface function .......................................................................... 30
Table 5-6. AUDIO device class request............................................................................................ 30
Table 5-7. AUDIO user interface functions ...................................................................................... 31
Table 5-8. CDC relevant descriptors ................................................................................................ 34
Table 5-9. CDC device class interface functions ............................................................................ 34
Table 5-10. CDC device class request ............................................................................................. 35
Table 5-11. CDC user interface functions........................................................................................ 35
Table 5-12. DFUrelevant descriptors ............................................................................................... 37
Table 5-13. DFU device class interface functions .......................................................................... 38
Table 5-14. DFU device class request.............................................................................................. 38
Table 5-15. DFU user interface functions ........................................................................................ 39
Table 5-16. MSC device class interface functions.......................................................................... 42
Table 5-17. MSC device class request ............................................................................................. 42
Table 5-18. MSC user interface functions ....................................................................................... 43
Table 5-19. HID relevant descriptors................................................................................................ 45
Table 5-20. HID device class interface functions............................................................................ 45
Table 5-21. HID device class request ............................................................................................... 45
Table 5-22. HID user interface functions ......................................................................................... 46
Table 5-23. printer device class interface function ........................................................................ 47
Table 5-24. printer device class request.......................................................................................... 47
Table 6-1. usbh_conf.h Configuration description......................................................................... 49

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Table 6-2. usb_conf.h Configuration description ........................................................................... 50
Table 6-3. USBFS host interrupt....................................................................................................... 52
Table 6-4. USB host library user interface function ....................................................................... 57
Table 6-5. HID host class library function ....................................................................................... 59
Table 6-6. MSC host class library function ..................................................................................... 60
Table 7-1. Revision history ............................................................................................................... 64

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1. Introduction
This application note is provided specifically for the GD32 MCU Universal Serial Bus full-
speed interface USBFS module. USBHS modules are the same as USBFS in general,
corresponding difference between USBFS and USBHS will be marked in the article. The
purpose of this note is to make it easier for customers to use the USBFS and USBHS firmware
library and to use this library for project development faster.
This application note is divided into four sections:
1. The architecture and files of the library;
2. Introduction to the bottom and middle layer driver functions of the library;
3. Introduction of the Device library;
4. Introduction to the Host library.
Table 1-1. Applicable products
Type
Product Model
MCU
FS
GD32F105xx series
GD32F107xx series
GD32F205xx series
GD32F207xx series
GD32F305xx series
GD32F307xx series
GD32F350xx series
GD32F4xx series
GD32E103xx series
GD32C103xx series
GD32E505xx series
GD32E507xx series
GD32E508xx series
GD32VF103xx series
GD32W515xx series
HS
GD32F4xx series
GD32E505xx series
GD32E507xx series
GD32E508xx series

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2. Library architecture and file structure
2.1. Library Architecture
USBFS module firmware structure of GD32 series is shown in Figure 2-1. GD32 USBFS
firmware library framework. The figure show USBFS host and device structure, user
application call the USBFS firmware library to realize the USB data commuction. The
underlying structure is hardware, that is MCU evaluation board. USBFS firmware library
consist of application layer and driver layer. User is able to modify application layer, while user
should not modify driver layer, which consist of host driver, device driver and USB underlying
layer. As a portion of application layer, USB application class file realize specific host or device
application class request. The library structure of USBFS and USBHS is similar.
Figure 2-1. GD32 USBFS firmware library framework
User application
main.c USB_Class
GD32xxx_standard_peripheral
&
CMSIS
drv_usb_host.h/.c
drv_usbh_int.h/.c
usbh_core.h/.c
usbh_enum.h/.c
drv_usb_core.h/c
GD32 USBFS driver
Application layer
USBFS interface
（GD32 MCU EVAL board）
USB host
main.c
USB_Class
USB device
USB host USB device
drv_usbd_int.h/.c
drv_usb_devcore.h/.c
usbd_core.h/.c
usbh_pipe.h/.c
drv_usb_regs.h
GD32xxxUSB firmware
usbh_usr.c
usbh_transc.h/.cusbd_enum.h/.c
usbd_transc.h/.c
Middle Bottom

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2.2. File structure
Take firmware library of GD32F4xx as an example, include the following four file folders.
Figure 2-2. USBFS Firmware Library Folder
Device file folder include Protocol layer files and device class files, which is required by USB
device.
Figure 2-3. Device folder
Driver folder include register definition, bottom layer driver and USB interrupt handler, which
is used to build device and host application.

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Figure 2-4. Driver folder
Host folder include register definition, bottom layer driver and USB interrupt handler, which is
required by USB host.
Figure 2-5. Host folder
The folder ustd include common device class file and standard enumeration file, which is
called by host and device.

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Figure 2-6. Ustd folder

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3. USBFS bottom driver
The file of USBFS bottom driver located in the driver folder. Bottom driver of whole firmware
library is directly relate to USB hardware module, which include register read-write and FIFO
operation, As shown in Table 3-1. USBFS underlying file.
Table 3-1. USBFS underlying file
Used range
File name
Functional description
general used
drv_usb_core.h/.c
USB core driver
drv_usb_regs.h
USB core bottom driver header file
drv_usb_hw.h
USB hardware configuration header file
The functions in the C file are described in detail below. As shown in Table 3-2. usb_core.h/.c
file function.
Table 3-2. usb_core.h/.c file function
Function name
Functional description
usb_core_reset
config USB core to soft reset
usb_basic_init
config USB core basic
usb_core_init
initializes the USB controller registers and prepares the core
device mode or host mode operation
usb_txfifo_write
write a packet into the Tx FIFO associated with the endpoint
usb_rxfifo_read
read a packet from the Rx FIFO associated with the endpoint
usb_txfifo_flush
flush a Tx FIFO or all Tx FIFOs
usb_rxfifo_flush
flush the entire Rx FIFO
usb_set_rxfifo
set Rx FIFO size
usb_set_txfifo
set Tx FIFO size
drv_usb_regs.h file define the whole USBFS module register content, all bottom layer
operation should call the file. drv_usb_hw.h file declare the relevant function about USB clock,
GPIO, delay, interrupt enable and CTC.

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4. USBFS middle layer driver
The middle driver layer is divided into host middle layer and device middle layer. Device
middle layer packages the transaction and basic function of USB device transfer. Host middle
layer packages the transaction and basic function of USB host transfer. As shown in Table
4-1. USBFS middle layer driver file.
Table 4-1. USBFS middle layer driver file
Range
folder
Function name
Functional description
Host
driver
drv_usb_host.h /.c
USB host mode low level driver
drv_usbh_int.h /.c
USB host mode interrupt handler file
host/core
usbh_core.h/.c
USB host core state machine driver
usbh_enum.h/.c
USB host mode enumberation driver
usbh_pipe.h/.c
USB host mode pipe operation driver
usbh_transc.c
USB host mode transactions driver
device
driver
drv_usb_dev.h /.c
USB device low level driver
drv_usbd_int.h /.c
USB device mode interrupt routines
device/core
usbd_core.h /.c
USB device mode core functions
usbd_enum.h /.c
USB enumeration function
usbd_transc.h/.c
USB transaction core functions
4.1. Host middle layer driver function
Table 4-2. drv_usb_host.h/.c file function
Function name
Functional description
usb_host_init
initializes USB core for host mode
usb_portvbus_switch
control the VBUS to power
usb_port_reset
reset host port
usb_pipe_init
initialize host pipe
usb_pipe_xfer
prepare host channel for transferring packets
usb_pipe_halt
halt pipe
usb_pipe_ping
configure host pipe to do ping operation
usb_host_stop
stop the USB host and clean up FIFO
Table 4-3. drv_usbh_int.h/.c file function
Function name
Functional description
usbh_isr
handle global host interrupt
usbh_int_port
handle the host port interrupt
usbh_int_pipe
handle all host channels interrupt
usbh_int_pipe_in
handle the IN channel interrupt
usbh_int_pipe_out
handle the OUT channel interrupt
usbh_int_rxfifonoempty
handle the rx fifo non-empty interrupt

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Function name
Functional description
usbh_int_txfifoempty
handle the TX FIFO empty interrupt
Table 4-4. usbh_core.h/.c file function
Function name
Functional description
usbh_init
USB host stack initializations
usbh_deinit
de-initialize USB host
usbh_class_register
USB host register device class
usbh_core_task
USB host core main state machine process
usbh_error_handler
handle the error on USB host side
usbh_sof
USB SOF callback function from the interrupt
usbh_connect
USB connect callback function from the interrupt
usbh_disconnect
USB disconnect callback function from the interrupt
usbh_port_enabled
USB port enable callback function from the interrupt
usbh_port_disabled
USB port disabled callback function from the interrupt
usbh_enum_task
handle the USB enumeration task
Table 4-5. usbh_enum.h/.c file function
Function name
Functional description
usbh_ctlstate_config
configure USB control status parameters
usbh_devdesc_get
get device descriptor from the USB device
usbh_cfgdesc_get
get configuration descriptor from the USB device
usbh_strdesc_get
get string descriptor from the USB device
usbh_setaddress
set the address to the connected device
usbh_setcfg
set the configuration value to the connected device
usbh_setinterface
set the interface value to the connected device
usbh_setdevfeature
set or enable a specific device feature
usbh_clrdevfeature
clear or disable a specific device feature
usbh_clrfeature
clear or disable a specific feature
usbh_nextdesc_get
get the next descriptor header
usbh_interface_select
select a interface
usbh_interface_find
find the interface index for a specific class
usbh_interfaceindex_find
find the interface index for a specific class interface and
alternate setting number
usbh_devdesc_parse
parse the device descriptor
usbh_cfgdesc_parse
parse the configuration descriptor
usbh_cfgset_parse
parse the configuration descriptor set
usbh_itfdesc_parse
parse the interface descriptor
usbh_epdesc_parse
parse the endpoint descriptor
usbh_strdesc_parse
parse the string descriptor
Table 4-6. usbh_pipe.h/.c file function
Function name
Functional description
usbh_pipe_create
create a pipe

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Function name
Functional description
usbh_pipe_update
modify a pipe
usbh_pipe_allocate
allocate a new pipe
usbh_pipe_free
free a pipe
usbh_pipe_delete
delete all USB host pipe
usbh_freepipe_get
get a free pipe number for allocation
Table 4-7. usbh_transc.h/.c file function
Function name
Functional description
usbh_ctlsetup_send
send the setup packet to the USB device
usbh_data_send
send a data packet to the USB device
usbh_data_recev
receive a data packet from the USB device
usbh_ctl_handler
USB control transfer handler
usbh_urb_wait
wait for USB URB(USB request block) state
usbh_setup_transc
USB setup transaction
usbh_data_in_transc
USB data IN transaction
usbh_data_out_transc
USB data OUT transaction
usbh_status_in_transc
USB status IN transaction
usbh_status_out_transc
USB status OUT transaction
usbh_request_submit
prepare a pipe and start a transfer
4.2. Device middle layer driver function
Table 4-8. drv_usb_dev.h/.c file function
Function name
Functional description
usb_devcore_init
initialize USB core registers for device mode
usb_devint_enable
enable the USB device mode interrupts
usb_transc0_active
active the USB endpoint 0 transaction
usb_transc_active
active the USB transaction
usb_transc_deactivate
deactive the USB transaction
usb_transc_inxfer
configure USB transaction to start IN transfer
usb_transc_outxfer
configure USB transaction to start OUT transfer
usb_transc_stall
set the USB transaction STALL status
usb_transc_clrstall
clear the USB transaction STALL status
usb_iepintr_read
read device IN endpoint interrupt flag register
usb_ctlep_startout
configures OUT endpoint 0 to receive SETUP packets
usb_rwkup_active
active remote wakeup signalling
usb_clock_active
active USB core clock
usb_dev_suspend
USB device suspend
usb_dev_stop
stop the device and clean up fifos
usb_dev_disconnect
config the USB device to be disconnected
usb_dev_connect
config the USB device to be connected

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Function name
Functional description
usb_devaddr_set
set the USB device address
usb_oepintnum_read
read device all OUT endpoint interrupt register
usb_oepintr_read
read device OUT endpoint interrupt flag register
usb_iepintnum_read
read device all IN endpoint interrupt register
usb_rwkup_set
set remote wakeup signalling
usb_rwkup_reset
reset remote wakeup signalling
Table 4-9. drv_usbd_int.h/.c file function
Function name
Functional description
usbd_int_dedicated_ep1out
USB dedicated OUT endpoint 1 interrupt service routine handler
usbd_int_dedicated_ep1in
USB dedicated IN endpoint 1 interrupt service routine handler
usbd_isr
USB device-mode interrupts global service routine handler
usbd_intf_outep
indicates that an OUT endpoint has a pending interrupt
usbd_intf_inep
indicates that an in endpoint has a pending interrupt
usbd_int_rxfifo
handle the RX status queue level interrupt
usbd_int_reset
handle USB reset interrupt
usbd_int_enumfinish
handle USB speed enumeration finish interrupt
usbd_int_suspend
USB suspend interrupt handler
usbd_emptytxfifo_write
check FIFO for the next packet to be loaded
Table 4-10. usbd_core.h/.c file function
Function name
Functional description
usbd_init
initailizes the USB device-mode stack and load the class driver
usbd_ep_setup
endpoint initialization
usbd_ep_clear
configure the endpoint when it is disabled
usbd_ep_recev
endpoint prepare to receive data
usbd_ep_send
endpoint prepare to transmit data
usbd_ep_stall
set an endpoint to STALL status
usbd_ep_stall_clear
clear endpoint STALLed status
usbd_fifo_flush
flush the endpoint FIFOs
usbd_connect
device connect
usbd_disconnect
device disconnect
usbd_addr_set
set USB device address
usbd_rxcount_get
get the received data length
Table 4-11. usbd_enum.h/.c file function
Function name
Functional description
usbd_standard_request
handle USB standard device request
usbd_class_request
handle USB device class request
usbd_vendor_request
handle USB vendor request
usbd_enum_error
handle USB enumeration error
int_to_unicode
convert hex 32bits value into unicode char
serial_string_get
get serial string

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Function name
Functional description
_usb_std_reserved
no operation, just for reserved
_usb_dev_desc_get
get the device descriptor
_usb_config_desc_get
get the configuration descriptor
_usb_bos_desc_get
get the BOS descriptor
_usb_str_desc_get
get string descriptor
_usb_std_getstatus
handle Get_Status request
_usb_std_clearfeature
handle USB Clear_Feature request
_usb_std_setfeature
handle USB Set_Feature request
_usb_std_setaddress
handle USB Set_Address request
_usb_std_getdescriptor
handle USB Get_Descriptor request
_usb_std_setdescriptor
handle USB Set_Descriptor request
_usb_std_getconfiguration
handle USB Get_Configuration request
_usb_std_setconfiguration
handle USB Set_Configuration request
_usb_std_getinterface
handle USB Get_Interface request
_usb_std_setinterface
handle USB Set_Interface request
_usb_std_synchframe
handle USB SynchFrame request
Table 4-12. usbd_transc.h/.c file function
Function name
Functional description
usbd_ctl_send
USB send data in the control transaction
usbd_ctl_recev
USB receive data in control transaction
usbd_ctl_status_send
USB send control transaction status
usbd_ctl_status_recev
USB control receive status
usbd_setup_transc
USB setup stage processing
usbd_out_transc
data out stage processing
usbd_in_transc
data in stage processing

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5. USBFS Device Library
USBFS device library is based on the above underlying layer and middle layer driver, which
include device library configuration, descriptor, interrupt, user interface, device class interface
and example introduction.
5.1. Device Library Configuration
Device configuration include two file, usbd_conf.h and usb_conf.h, which is located in project
file folder, while device configuration file and other driver file are stored in same directory.
5.1.1. usbd_conf.h
The file configuration options are as follows:
#define USBD_CFG_MAX_NUM 1
#define USBD_ITF_MAX_NUM 1
#define USBD_HID_INTERFACE 0
/* USB user string supported */
/* #define USB_SUPPORT_USER_STRING_DESC */
#define HID_IN_EP EP1_IN
#define HID_IN_PACKET 8
Each configuration is defined as follows Table 5-1. usbd_conf.h configuration description.
Table 5-1. usbd_conf.h configuration description
Configuration name
Functional description
USBD_CFG_MAX_NUM
configuration maximum number
USBD_ITF_MAX_NUM
interface maximum number
USBD_HID_INTERFACE
Device class index
HID_IN_EP
IN endpoint index
HID_IN_PACKET
endpoint data packet length
5.1.2. usb_conf.h
The usb_conf.h file mainly define FIFO allocation of USBFS module. USBFS has 1.25KB
RAM buffer, that is 320 words FIFO. While, USBHS has 4KB RAM buffer, that is 1024 words
FIFO.
The file configuration options are as follows:

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#ifdef USB_FS_CORE
#define RX_FIFO_FS_SIZE 128
#define TX0_FIFO_FS_SIZE 64
#define TX1_FIFO_FS_SIZE 128
#define TX2_FIFO_FS_SIZE 0
#define TX3_FIFO_FS_SIZE 0
#endif /* USB_FS_CORE */
#define USB_SOF_OUTPUT 1
#define USB_LOW_POWER 1
//#define VBUS_SENSING_ENABLED
//#define USE_HOST_MODE
#define USE_DEVICE_MODE
//#define USE_OTG_MODE
Table 5-2. usb_conf.h configuration description
Configuration name
Functional description
RX_FIFO_FS_SIZE
RX FIFO size configuration
TX_FIFO_FS_SIZE
TX FIFO size configuration
USB_SOF_OUTPUT
enable SOF output
USB_LOW_POWER
enable low power mode
VBUS_SENSING_ENABLED
enable VBUS SENSING
USE_HOST_MODE
host mode
USE_DEVICE_MODE
device mode
USE_OTG_MODE
OTG mode
Note:
1. If user need to measure the SOF with an oscilloscope, it is necessary to configure the
PA8 pin as the output function.
2. Only one of USE_HOST_MODE, USE_DEVICE_MODE and USE_OTG_MODE coule be
selected.
3. GD32F105xx/107xx and GD32F205xx/F207xx series don`t has
VBUS_SENSING_ENABLED function, if USB module is configured as device, user
should connect VBUS pin.
5.2. Firmware library process
USBFS firmware library flow include clock configuration, interrupt enable, USB register
configuration, endpoint configuration, connect, enumeration and data transfer.As shown in
Figure 5-1. Firmware library flowchart.

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Figure 5-1. Firmware library flowchart
USB clock configuration
USB timer configuration
User interface function register
start
Device class interface function register
Get serial string
USB basic / core initialization
usb_rcu_config
usb_timer_init
hid_itfop_register
udev->dev.class_core = class_core;
serial_string_get
usb_basic_init / usb_core_init
usbd_disconnectUSB device disconnect
USB FIFO、endpoint、interrupt enable usb_devcore_init
USB device connect usbd_connect
USB interrupt configuration usb_intr_config
Enumeration process
Data transfer process
Interrupt handle
Corresponding function
5.3. Descriptor
The descriptors of the USBFS device library are contained in the device class file, as shown
in the Figure 5-2. Device class file path.