USB emulated U disk

USB emulated U disk1、software to hardware2、Brief principle2.1、Hardware schematic diagram2.2、Physical connection diagram2.3、Principle of control3、Engineering configuration3.1、Notes3.2、Pin configuration4、Main Function4.1、User function4.2、HAL library function parsing5、Experimental phenomenon

This tutorial demonstrates: using USB Full Speed Device interface to simulate USB flash drive to store files (OLED display W25Q64, STM32 USB connection information).

1、software to hardware

STM32F103CubeIDE
STM32 robot expansion board
USB: Chip internal peripheral
W25Q64: Onboard
OLED: External
Type-Cv cable or ST-Link
Download or simulate the program of the development board

2、Brief principle

2.1、Hardware schematic diagram

2.2、Physical connection diagram

OLED	STM32 board
VCC	VCC
SCL	SCL
SDA	SDA
GND	GND

STM32 USB	PC
Type-C interface	USB interface


The Type-C data cable was used to connect the computer to the STM USB interface

2.3、Principle of control

USB：(Universal Serial Bus)

USB	Characteristics
Class of speed	Low speed（USB1.0：1.5Mbps） Full speed（USB1.1：12Mbps） High speed（USB2.0：480Mbps） Super high speed（USB3.0：5Gbps、USB3.1：10Gbps） The development board is in full speed mode
Communication interface	Development board uses 16-pin Type-C interface (see schematic)
Data transfer	Control transmission Interrupt transmission Bulk transfer Isochronous transmission
Advantages	1. Support hotplugging and PNP (Plug-and-Play); 2. Provide USB peripherals with various speed levels to adapt to different requirements; 3. The port has very flexible expansibility; 4. Provides a single, easy-to-use standard connection type; 5. To meet the requirements of various types of peripheral devices, USB provides four different data transfer types.

USB Protocol

The USB bus uses differential signal transmission, where D+ and D- represent the positive and negative data lines of the differential signal respectively.

USB1.1 and USB2.0 use a differential signal level of 3.3V and USB3.0 uses a differential signal level of 5V.


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USB related knowledge can go to the "USB Encyclopedia of USB Chinese network" for understanding and learning, the following only introduces the common concepts

Full speed/low speed USB bus device connection method

High speed/full speed equipment：D+ connected with 1.5k pull-up resistor;

Low speed equipment: D-connected 1.5k pull-up resistor;

Bus status

Level type	Scope
Difference 1	D+>2.8V，D-<0.3V
Difference 0	D+<0.3V，D-<0.3V
Single ended 0（SE0）	D+<0.3V，D-<0.3V
Single ended 1（SE1）	D+>2.8V，D->2.8V
J state： Low speed Full speed High speed	Difference 0 Difference 1 Difference 1
K state Low speed Full speed High speed	Difference 1 Difference 0 Difference 0
Restore status	K state
Packet start（SOF）	The USB data bus switches from the idle state to the K state
Packet end（EOP）	The SE0 lasts for two basic time units, and the J state lasts for one time unit

Encoding of USB signals

The data in USB is encoded by NRZI (none-return to zero inverted), and the different states of D+ and D- lines are defined as J and K.

Encoding/decoding of data (reverse non-return-to-zero code)


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Note: The edge that meets 0 changes its state. If it is 1, the original state remains
Before the data is NRZI encoded, a 0 signal is inserted after every six consecutive 1 signals so as not to lose synchronization.

USB Protocol layer

Packet is the basic unit of information transmission in USB system. All data is transmitted on the bus after being packaged.

Each packet consists of six parts: synchronization field (SYNC), packet identifier (PID), address field (ADDR), DATA field (including frame number), validation field (CRC), End of Packet (EOP).

USB包

Practical Applications

The STM32F103ZET6 has an embedded device controller compatible with full speed USB, which complies with the standard for full speed USB devices (12 MBPS).

The USB-specific 48MHz clock is generated directly from the internal main PLL (the clock source must be a HSE crystal oscillator).

surce file	function
usb_device.c	USB device initialization function
usbd_conf.c	USB protocol parameters, GPIO initialization, and other functions
usbd_storage_if.c	USB storage device related functions
usbd_desc.c	USB descriptor and USB enumeration processing


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USB related knowledge does not do too much introduction, you can consult the information on the Internet, mainly introduces the functions used in engineering

3、Engineering configuration

Project Configuration: Prompts for configuration options in the STM32CubeIDE project configuration process

3.1、Notes

Omitted project configuration: New project, chip selection, project configuration, SYS for pin configuration, RCC configuration, clock configuration, and project configuration content

The project configuration part, which is not omitted, is the key point to configure in this tutorial.


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Please refer to [2. Development environment construction and use: STM32CubeIDE installation and use] to understand how to configure the omitted parts of the project.

3.2、Pin configuration

Configure the specified pin function

You can directly select the corresponding pin number in the pin view, and the corresponding option will appear when the mouse is left clicked

I2C

SPI

USB

Clock Configuration

Advanced Settings

Generating code

4、Main Function

This section mainly introduces the functional code written by users. Detailed code can be opened by yourself in the project file we provide, and enter the Bsp folder to view the source code. .

4.1、User function

Functions that were covered in the previous tutorial will not be covered

function：VCP_Status

Function prototypes	void VCP_Status(void)
Functional Description	Check the USB connection status
Input parameters	None
Return value	None

4.2、HAL library function parsing

The HAL library functions that were covered in the previous tutorial will not be covered


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If you want to find the HAL library and LL library function analysis involved in the entire tutorial, you can view the documents in the folder [8. STM32 Manual: STM32F1_HAL Library and LL Library_User Manual]

function：MX_USB_DEVICE_Init

Function prototypes	void MX_USB_DEVICE_Init(void)
Functional Description	Initialize the USB device
Input parameters	None
Return value	None

function：MX_USB_DEVICE_Init

Function prototypes	USBD_StatusTypeDef USBD_Init (USBD_HandleTypeDef pdev, USBD_DescriptorsTypeDef pdesc, uint8_t id)
Functional Description	Initialize the configuration and parameters of the USB device
Input parameters1	pdev：Handle to a USB device
Input parameters2	pdesc：USB device descriptor information
Input parameters3	id：The identifier of the USB device
Return value	USB status：USBD_OK、USBD_BUSY、USBD_FAIL

function：USB_LP_CAN1_RX0_IRQHandler

Function prototypes	void USB_LP_CAN1_RX0_IRQHandler(void)
Functional Description	Handle USB_LP_CAN1_RX0_IRQn interrupt (USB low priority and CAN1 receive 0 interrupt)
Input parameters	None
Return value	None

5、Experimental phenomenon

After downloading the program successfully, press the RESET button of the development board to observe the OLED display and LED display


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For program download, please refer to [2. Development environment construction and use: program download and simulation]

phenomenon：

The STM32 USB interface is not connected：

The first line of OLED shows: "W25Q64 find! "

OLED second line: "USB disconnect"

Connect the STM32 USB port：

The first line of OLED shows: "W25Q64 find! "

OLED second line: "USB connect"

The USB flash drive recognized by the system for the first time, needs to be formatted to open it；

Format U disk must carefully check the label, do not format other disks, otherwise the data in the disk will be lost


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SPI FLASH has a limit to write data, it is best not to write data to it frequently, otherwise it is easy to write SPI FLASH bad

Note the Type-C data line interface location for the following experimental phenomena