参考仓库: https://github.com/rzeldent/esp32cam-rtsp

Objective

Stream video through wifi using ESP-32-CAM.
The video sources can be accessed by an ip address.

Implemenation

Install PlatformIO plugin in vscode.
Clone the repository

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git clone --recursive https://github.com/rzeldent/esp32cam-rtsp.git

Use vscode pio to open the project. Wait pio till its configuration is done.

Change the default_envs settings, here I use esp32cam_ai_thinker

If no default_envs is specified, pio will build the project for all platforms

Here we can build and upload the program to the board.

Connect to ESP**** WiFi, and visit http://192.168.4.1 to configure the wifi settings of the board. I choose to my phone’s hot spot.

Then open the monitor to check the ip address (you need to connect your computer to the same LAN (local area network) to visit the ip)

Visit the 192.168.23.142 and you will see the page (similar with the page of http://192.168.4.1):

Click rtsp://192.168.23.197:554/mjpeg/1 and you will see the streaming video:

生无可恋做横向.jpg

Standard Toolchain Setup

Guide: https://docs.espressif.com/projects/esp-idf/en/stable/esp32/get-started/linux-macos-setup.html#

ESP_IDF

I directly download the archive with all the submodules included: https://github.com/espressif/esp-idf/releases/tag/v5.3.1

This archive can also be downloaded from Espressif’s download server: https://dl.espressif.com/github_assets/espressif/esp-idf/releases/download/v5.3.1/esp-idf-v5.3.1.zip

cd into the unzip folder (The installation will fail in conda venv)

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conda deactivate
./install.sh
. ./export.sh

In ~/.zshrc

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alias get_idf='. $HOME/esp/esp-idf-v5.3.1/export.sh'

Then each time I need to setup esp32 development environment, I only need to type get_idf.

Some useful commands

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idf.py set-target esp32
idf.py menuconfig
idf.py build
idf.py -p /dev/ttyUSB0 -b 115200 flash
idf.py -p /dev/ttyUSB0 -b monitor
idf.py -p /dev/ttyUSB0 flash monitor # combine together

PlatformIO

事实证明pio是最方便的。。
事前安装过pio的vscode插件，直接打开pio的esp32项目就直接可以编译上传以及查看串口监视器。

L2 (Embedded system overview)

Take a look at the differences between Microprocessor (in our personal computer or phone) and Microcontroller

In embedded system, harvard architecture is widely used.
Our board (STM32F103C8T6) use harvard architecture on physical level (refer to the block diagram in reference manual)

However, in the software level, we treat the instruction memory and data memory as a whole block of memory (therefore, it is more accurate to say that the stm32 uses a mixed Harvard and von Neumann architecture.).

In stm32, instruction memory, data memory, registers of peripherals/IO are all mapped to memory.

L3 (Programming)

Type Qualifiers

const

• implies that value not supposed to be written by program (read only) during run-time. Can be modified by others like hardware.

  If you want to save the limited RAM spaces (data memory) for other variables, you can use this keyword to store this variable in ROM (program memory). It’s important for harvard architecture.

volatile

• indicate the value can be changed by something other than program so it should be reexamined frequently.

  This means two things:

  • The compiler will not try to optimize the variable with volatile. See the two examples on slides.
  • Each time the program reads the volatile variable, the processor will not look into cached data memory, meaning that the program can always get the newest updated data in memory (which is very important when external hardware change the variable). However, this case is not relevant with STM32 MCU since it didn’t have cache.

What about const volatile ?

• The combination of the above two concepts. Usually used to declare pointers
  Example:
  const volatile char *a declares a pointer pointing to a value that cannot be changed by the program through *a, but the value of a can be changed (pointing to another value). *a = 0 is not allowed, a = &b is allowed.

Generally, we use const volatile to declare pointers that points to hardware registers or memory-mapped Input ports(read only).

Basic Program Structure

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// import header file for the board (containing the declaration of SFR)
// declare global variables
int main(void){
	// initialization (system clock, peripherals)
	while(true) // super loop, the the program alive
	{
		// interact with peripherals
	}

}

How to interact with peripherals

We need to use C code to set the value of SFR.

SFR (special function registers)

These are registers that are embedded in peripherals, used for configuration and control of peripherals.

VERBOSE~
If we want to get the status of a peripheral, we read the value of SFR.
If we want to send something to peripheral, we write value to SFR.

Let’s take timer as an example:
SFR in block diagram of timer:

SFR declaration in code:

We change operate with these registers through Bit Operation.

L4 (IO)

All the modes of GPIO:

You may see an unfamiliar unit

Input

After we configured the GPIO to be input ports, the output driver is disabled (disconnected).

Pull down

Pull up

Floating

General Purpose Output

The input driver part is still enabled so that we can read the output status.

Open Drain

Can “generate” voltage higher than VDD at IO pin.

Push Pull

Most common one.

Alternative Function Output

Not covered.

L5 (Interrupts)

Why interrupt?

Peripherals inform the processor through external interrupt.

Where do interrupts come from

We mainly deal with the interrupts from peripherals.

How to handle interrupts

Through interrupt service routine (ISR)

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| Vector Number | Interrupt Number | Description                    | Vector Address   |
|---------------|------------------|--------------------------------|------------------|
| 0             | -                | Initial Stack Pointer          | 0x0800 0000      |
| 1             | -                | Reset Handler                  | 0x0800 0004      |
....
| 27            | 11               | DMA1 Channel1 global Interrupt | 0x0800 006C      |
| 28            | 12               | DMA1 Channel2 global Interrupt | 0x0800 0070      |
| 29            | 13               | DMA1 Channel3 global Interrupt | 0x0800 0074      |
| 30            | 14               | DMA1 Channel4 global Interrupt | 0x0800 0078      |
| 31            | 15               | DMA1 Channel5 global Interrupt | 0x0800 007C      |
| 32            | 16               | DMA1 Channel6 global Interrupt | 0x0800 0080      |
| 33            | 17               | DMA1 Channel7 global Interrupt | 0x0800 0084      |
...
| 41            | 25               | TIM1 Break Interrupt           | 0x0800 00A4      |
| 42            | 26               | TIM1 Update Interrupt          | 0x0800 00A8      |
| 43            | 27               | TIM1 Trigger and Commutation   | 0x0800 00AC      |
| 44            | 28               | TIM1 Capture Compare Interrupt | 0x0800 00B0      |
...

This is an arbitrary IVT that depicts the pattern of IVT, for detailed IVT of STM32, please refer to the reference manual.

What to do inside ISR

• Always remember to clear the interrupt flag in ISR.
• Because there is often more interrupt sources than interrupt vectors, you need to judge which source triggered this interrupt based on interrupt status register.
• Customized operation… (but be short, because if the operation take too many clock cycles, it may be interrupted by another interrupt source, which may not be on purpose)

Nested interrupts

L6 (Timer)

Let’s split Timer peripheral into 3 parts:

The reset frequency of the counter is $$\frac{f_{input}}{(Prescaler+1)\times(Counter Period+1)}$$

Red part: Timer-channels unit

The timer channels are the working elements of the timer.
They are the means by which a timer peripheral interacts with its external environment (through input capture or output compare).

How to use multiple timer for more counting digits (32-bit)

L7 (LCD)

Just refer to RC2_LCD. I think it’s not the focus of final exam.

L9 & L10 (Input Capture & Output Compare)

IC is a peripheral that can monitor the input signal changes (pos/neg edge) independent of the processor (Core).
OC is a peripheral that can generate precise output signal independent of the processor (Core).

In STM32, it is embedded in timer peripheral (together with output compare).

IC

You can consider IC as a timer value recorder. It will record the timer value each time the capture condition is met (you can see from the diagram, the timer value is from CNT counter).

These conditions can be:

• rising edge
• falling edge
• both
  With a prescaler, we trigger capture events every few edges.
  Similar for interrupt, we can trigger an interrupt every few captures.

Note:
The IC does not capture the edge immediately when a rising or falling edge happened. The capture event needs to be sync with PB_clk.
Further more, the module will capture the timer counter value that is valid 2-3 PB_clk cycles after the capture event.

For detailed configuration, please refer to Reference Manual.pdf on canvas, page 349-359, 382-385.

OC

Just refer to RC2_Output_Campare and RC3_Lab4 for the concepts and PWM configuration.
Also, the solution of hw2 has been uploaded to canvas, please take a look.

For this RC, we will go through Lab 4 in detail.

CubeMX

We need to generate PWM signal on PB14(embeded with an LED D1, or D2 if you like)

In STM32, Input Capture and Output Compare is configured in Timer channels.

Let’s check which Timer is connected to PB14

Then we configure timer 1.

Also remember to configure PB12 (SW4) as GPIO_Input.

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/* USER CODE BEGIN 2 */
HAL_TIM_PWM_Start(&htim1, TIM_CHANNEL_2);
HAL_TIMEx_PWMN_Start(&htim1, TIM_CHANNEL_2);
/* USER CODE END 2 */

Change PWM duty cycle:

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void ChangeDutyCycle(int pulse_width)
{
    __HAL_TIM_SET_COMPARE(&htim1, TIM_CHANNEL_2, pulse_width);
    // htim1.Instance->CCR2 = pulse_width;
}

Get the press/release action of the button (PB12):

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int pressed = 0;
   /* USER CODE BEGIN WHILE */
   while (1) { // main loop
       /* USER CODE END WHILE */
       /* USER CODE BEGIN 3 */
       if (!HAL_GPIO_ReadPin(GPIOB, GPIO_PIN_12) && pressed == 0) {
           pressed = 1;
           // what to do when pressed
       }
       else if (HAL_GPIO_ReadPin(GPIOB, GPIO_PIN_12) && pressed == 1) {
           pressed = 0;
           // what to do when releassed
       }
   }
   /* USER CODE END 3 */

Input Compare Module

IC is a peripheral that can monitor the input signal change (pos/neg edge) independent of the processor (Core).

For detailed configuration, please refer to Reference Manual.pdf on canvas, page 349-359, 382-385.

Some useful documentation on the configuration register:

Datasheet for HD44780: https://www.sparkfun.com/datasheets/LCD/HD44780.pdf

LCD Controller Pin

1. VSS (Pin 1): Ground (GND).
2. VDD (Pin 2): Power supply (usually +5V).
   Note: If you use J-link debugger to power the board, the output voltage at +5V pin will not be 5V, maybe around 2.8V, so remember to use the 5V power supply wire to power the board.
3. VO (Pin 3): Contrast adjustment pin. Usually connected to a potentiometer to adjust the contrast.
4. RS (Pin 4): Register select pin. Low for instruction register, high for data register.
5. RW (Pin 5): Read/Write pin. Low for write operation, high for read operation. Usually grounded (write mode).
6. E (Pin 6): Enable pin. The LCD controller only captures (grabs) the data presented at its register lines(D0-D7) only when the E pin “transitions” from high to low.
7. D0-D7 (Pins 7-14): Data bus pins. Used for communication with the microcontroller in either 4-bit (D4-D7) or 8-bit (D0-D7) mode.
8. A (Pin 15): For the backlight. Typically connected to +5V.
9. K (Pin 16): For the backlight. Typically grounded (GND).

Connection with STM32

Some Useful Charts

From datasheet

1. Four operation
   
   **IR: instruction register** **DR: data register**

In this Lab, we will mainly use the first and third operation

2. Instruction

   
   

3. DDRAM

   

4. CGRAM

   

Application Example

Send Command to LCD Controller

Recall the operation:

1. Set the pin of RS & R/W to low.
2. Set E to high, preparing for the data transfer.
3. Set D7-D0 to the desired instruction(8-bit).
4. Set E to low

Sample code:

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void LCD_Write_Command(uchar Com) {
  Delay_ms(10);
  HAL_GPIO_WritePin(GPIOB, LCD_RS_Pin, GPIO_PIN_RESET); // LCD_RS = 0;
  HAL_GPIO_WritePin(GPIOB, LCD_RW_Pin, GPIO_PIN_RESET); //	LCD_RW = 0;
  HAL_GPIO_WritePin(GPIOB, LCD_E_Pin, GPIO_PIN_SET);    // LCD_E_Pin = 1;
  Delay_ms(1);                                          // wait for tpw;

  LCD_PORT = Com;// put command on the bus

  HAL_GPIO_WritePin(GPIOB, LCD_E_Pin, GPIO_PIN_RESET); // LCD_E_Pin =0;
  Delay_ms(1);                                         // wait for tpw;

}

Write Data To DDRAM

Recall the operation:

1. Set the pin of RS to high and R/W to low.

2. Set E to high, preparing for the data transfer.

3. Set D7-D0 to the desired address.

   

4. Set E to low

Sample code:

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void LCD_Write_Data(uchar dat) {
  Delay_ms(1);

  HAL_GPIO_WritePin(GPIOB, LCD_RS_Pin, GPIO_PIN_SET);   // LCD_RS = 1;
  HAL_GPIO_WritePin(GPIOB, LCD_RW_Pin, GPIO_PIN_RESET); //	LCD_RW = 0;
  HAL_GPIO_WritePin(GPIOB, LCD_E_Pin, GPIO_PIN_SET);    // LCD_E_Pin = 1;
  // Delay_ms(1);

  LCD_PORT = dat; // put data on the bus

  HAL_GPIO_WritePin(GPIOB, LCD_E_Pin, GPIO_PIN_RESET); // Set LCD_E = 0;

  Delay_ms(1); // wait for tpw;
}

Init LCD

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#define LCD_2_LINE_4_BITS 0x28
#define LCD_2_LINE_8_BITS 0x38
#define LCD_DSP_CSR 0x0c
#define LCD_CLR_DSP 0x01 
#define LCD_CSR_INC 0x06

void LCD_init(void)
{
  LCD_Write_Command(LCD_2_LINE_8_BITS); // function set -8 bit interface
  Delay_ms(5);
  LCD_Write_Command(LCD_2_LINE_8_BITS); 
  
  LCD_Write_Command(LCD_CLR_DSP); // clear display
  Delay_us(100);
  LCD_Write_Command(LCD_CSR_INC); // Set entry mode: increment
  Delay_us(100);
  LCD_Write_Command(LCD_DSP_CSR); // open display, close cursor
}

Display Charactor

First we need to set the cursor position

The cursor position is basically the DDRAM address that you want to write data in, which is corresponding to the display location on LCD screen.

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void LCD_Set_Position(uchar x, uchar y) {
  if (y == 0) // first line
  {
    LCD_Write_Command(0x80 + x);
  } else if (y == 1) // second line
  {
    LCD_Write_Command(0xc0 + x);
  }
}

If we want to display a character at first line, first column:

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LCD_Set_Position(0,0);

Then, we need to write data into DDRAM[addr] to tell the LCD which character you want to display, for example “J”.

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LCD_Write_Data("J"); // send the ascii code

Putting them all together:

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void LCD_Display_Char(uchar Char, uchar x, uchar y)
{
  LCD_Set_Position(x, y);
  LCD_Write_Data(Char);
}

Display String

The cursor will shift right (because we set increment entry mode) after each write_data operation, so displaying a string is quite simple.

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void LCD_Display_Char(uchar Char, uchar x, uchar y) // 显示字符ASCII码
{
  LCD_Set_Position(x, y);
  LCD_Write_Data(Char);
}

Demo

…

Output Compare Module

OC is a peripheral that can generate precise output signal independent of the processor (Core).

Drive high, drive low, toggle

Dual Compare

Single pulse, continuous.

PWM

System used: Archlinux

Pre-requirements

• c language server (for completion, diagnostics), e.g. clangd
• A code editor that use language server, e.g. vscode, vim/neovim

Install Related Softwares

STM32CubeMX

STM32CubeMX is mainly responsible for generating the project with your configuration.

For Distro like Ubuntu/Debain, you can go to the ST official site
Or you can install the software through distro repository

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yay -S stm32cubemx

For Arch, you need to modify the AUR repository (I mean, maybe the maintainer doesn’t do a good job).
The URL for the repository:https://aur.archlinux.org/packages/stm32cubemx

First clone the repository

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git clone https://aur.archlinux.org/stm32cubemx.git

Modify the required jdk version in file stm32cubemx.sh
from exec archlinux-java-run --min 17 -- -jar /opt/stm32cubemx/STM32CubeMX "$@" to exec archlinux-java-run --min 17 --max 20 -- -jar /opt/stm32cubemx/STM32CubeMX "$@"

Then build and install the STM32CubeMX

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makepkg --noconfirm --skipinteg -si

Since STM32CubeMX is not compatible with jdk22 (which is the default jdk that arch is currently using), you need to install jdk17 through yay -S jdk17-openjdk

Then you can start STM32CubeMX by running stm32cubemx, and hopefully, everything is fine.

Compiler

Use arm-none-eabi-gcc

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yay -S arm-none-eabi-gcc
yay -S arm-none-eabi-newlib

Debugger

Use OpenOCD to burn and debug STM32 through STLink v2 (the blue USB device provided by us).

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yay -S openocd

Setup Your STM32 Project

Open your STM32CubeMX, follow the instruction of Lab1.pdf to configure your project.

NOTE: In Project Manage -> Project -> Project Settings -> Toolchain / IDE, use Makefile/CMake.

Generate the code and go to the project directory (with Makefile/CMakeLists.txt in the directory).

Then you need to generate the compile_commands.json for clangd to recognize the project.

Makefile

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bear -- make

CMake

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cmake -S ./ -B ./build

Build Project

Makefile

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make

Then target binary file is ./build/<Project Name>.bin

CMake

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cmake --build ./build

Then target binary file is ./build/<Project Name>.elf

Load to STM32F103C8T6

Use OpenOCD to load the binary file to the board.

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sudo openocd -f /usr/share/openocd/scripts/interface/stlink.cfg -f /usr/share/openocd/scripts/target/stm32f1x.cfg -c "program ./build/<Project Name>.bin reset exit 0x8000000"

Result

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Open On-Chip Debugger 0.12.0
Licensed under GNU GPL v2
For bug reports, read
	http://openocd.org/doc/doxygen/bugs.html
Info : auto-selecting first available session transport "hla_swd". To override use 'transport select <transport>'.
Info : The selected transport took over low-level target control. The results might differ compared to plain JTAG/SWD
Info : clock speed 1000 kHz
Info : STLINK V2J37S7 (API v2) VID:PID 0483:3748
Info : Target voltage: 3.222587
Info : [stm32f1x.cpu] Cortex-M3 r1p1 processor detected
Info : [stm32f1x.cpu] target has 6 breakpoints, 4 watchpoints
Info : starting gdb server for stm32f1x.cpu on 3333
Info : Listening on port 3333 for gdb connections
[stm32f1x.cpu] halted due to debug-request, current mode: Thread
xPSR: 0x01000000 pc: 0x08000dc8 msp: 0x20005000
** Programming Started **
Info : device id = 0x20036410
Info : flash size = 64 KiB
** Programming Finished **
** Resetting Target **
shutdown command invoked

NOTE: In different Distro, the cfg file for OpenOCD may locate in different directories. You need to find it by yourselves.

By the way, if you use CMake

Note: When uploading binary file to STM32, it’s recommended to use .bin file instead of .elf file.
Please use the following script to convert the .elf to .bin and upload.

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cmake -DCMAKE_EXPORT_COMPILE_COMMANDS=ON .
cmake --build  ./build 
arm-none-eabi-objcopy  -O binary -S ./build/*.elf ./build/target.bin
sudo openocd -f /usr/share/openocd/scripts/interface/stlink.cfg -f /usr/share/openocd/scripts/target/stm32f1x.cfg -c "program ./build/target.bin reset exit 0x8000000"

Debug

You have three possible choices. I recommend using Ozone.

openocd+gdb+gdbfrontend(not recommended)

reference:
https://rohanrhu.github.io/gdb-frontend/tutorials/embedded-debugging/

openocd+vscode+PlatformIO (not recommended)

reference:
https://blog.csdn.net/qq_41757528/article/details/127741620

Segger Ozone!!!

reference:
https://blog.csdn.net/weixin_41572450/article/details/124710818

Maybe the best debug tool for stm32

To use segger ozone, you need a different linker called jlink (originally we use st-link v2). You need to buy this linker first (maybe on Taobao or Amazon).

Install Ozone through:

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yay -S ozone

Setup of ozone project:

• Start Ozone
• Choose Device
  • Device: STM32F103C8
  • Register Set: Cortex-M3
  • Peripherials (optional): /opt/SEGGER/Ozone/Config/Peripherals/STM32F103xx.svd
• Connection Settings
  • Target Interface: SWD
  • Target Interface Speed: 4MHz
  • Host Interface: USB
• Program File: select the binary file you have built (.elf is recommended).

Debug:

set some breakpoints and watch some variables of your interest.
Press the green “power” icon on the upper left corner to start (upload the program and start the debugging process)
Press the blue “play” icon besides “power” to continue.

Embeded System

Microprocessor

peripheral chips are needed to construct a product

Microcontroller

processor an peripheral functions implemented on a VLSI chip

Processing speed much slower and energy consuming is much lower