解释一下下面这段代码，分段解释并补充需要了解的知识     # Hello World Example
#
# Welcome to the CanMV IDE! Click on the green run arrow button below to run the script!

import sensor, image, time, lcd, struct, ustruct
import gc

from machine import UART,Timer,PWM
from board import board_info
from fpioa_manager import fm
import KPU as kpu
from Maix import GPIO,utils
import gc
import machine

lcd.init()                          # Init lcd display
lcd.clear(lcd.RED)                  # Clear lcd screen.

sensor.reset(freq=22000000, dual_buff=1)                # 设置摄像头频率 24M 开启双缓冲模式 会提高帧率 但内存占用增加
sensor.set_auto_exposure(0)         # 设置自动曝光
sensor.set_auto_gain(False) # 颜色跟踪必须关闭自动增益
sensor.set_auto_whitebal(False) # 颜色跟踪必须关闭白平衡
sensor.set_pixformat(sensor.RGB565) # Set pixel format to RGB565 (or GRAYSCALE)
sensor.set_framesize(sensor.QVGA)   # Set frame size to QVGA (320x240)

#kpu = KPU()
#kpu.load_kmodel("/sd/KPU/mnist/uint8_mnist_cnn_model.kmodel")
sensor.skip_frames(time = 2000)     # Wait for settings take effect.
clock = time.clock()                # Create a clock object to track the FPS.
sensor.set_auto_exposure(0)         # 设置自动曝光

sensor.set_vflip(1)
#______________________________________________________________________________________________________________________________
#打印内存分配情况
print(utils.gc_heap_size())
print("stack mem:"+str(gc.mem_free() / 1024)) # stack mem
print("heap mem:"+str(utils.heap_free() / 1024)) # heap mem

#第一次用执行一次下面这两个语句
#utils.gc_heap_size(800*1024)
#machine.reset()

#______________________________________________________________________________________________________________________________
#程序运行选择
is_need_debug = 0
is_patrol_line = 0
is_upacker_debug = 0
is_stack_heap_mem_debug = 0
is_upacker_recive_debug = 1
is_findflob_debug = 0

#______________________________________________________________________________________________________________________________
#程序运行状态
work_mode = 0  #0是巡线模式，1是数字识别模式

#______________________________________________________________________________________________________________________________
#串口配置区

fm.register(6, fm.fpioa.UART1_TX, force=True)
fm.register(7, fm.fpioa.UART1_RX, force=True)

k210_uart = UART(UART.UART1, 921600, 8, 0, 0, timeout=1000, read_buf_len=4096)

uart_test_write_str = '1260808878'

#______________________________________________________________________________________________________________________________
#按键蜂鸣器配置区
#注册IO，注意高速GPIO口才有中断
fm.register(35, fm.fpioa.GPIO0)
fm.register(16, fm.fpioa.GPIOHS0)
#构建案件对象
KEY=GPIO(GPIO.GPIOHS0, GPIO.IN, GPIO.PULL_UP)

#PWM通过定时器配置，接到IO15引脚
tim = Timer(Timer.TIMER1, Timer.CHANNEL0, mode=Timer.MODE_PWM)
beep = PWM(tim, freq=1000, duty=0, pin=9)

#按键标志位
key_node = 0
key_press_long = 0

#中断回调函数
def fun(KEY):
    global work_mode,key_node,key_press_long
    temp_count = 0

    time.sleep_ms(10) #消除抖动
    while KEY.value()== 0:
        key_node = 1
        time.sleep_ms(10) #长按延时
        #长按检测计数
        temp_count=temp_count+1
        print(temp_count)
    if temp_count >= 50:

        beep.duty(50)
        time.sleep_ms(500)
        beep.duty(0)
        time.sleep_ms(100)

        print(temp_count)
        key_node = 0
        key_press_long = 1

#开启中断，下降沿触发
KEY.irq(fun, GPIO.IRQ_FALLING)

#______________________________________________________________________________________________________________________________
#要传给梁山派的数据

#work_mode：0是巡线模式，1是数字识别模式
#recognition：0是未知（巡线状态下），1是药房门口区域（停车线）,十字路口和T字路口由

class uart_send_data_t:
   def __init__( self, work_mode=0, recognition=0,top_block_offset=0,center_block_offset=0,left_block_offset=0,right_block_offset=0,left_number = 0,right_number = 0):
      self.work_mode = work_mode
      self.recognition = recognition
      self.top_block_offset = top_block_offset
      self.center_block_offset = center_block_offset
      self.left_block_offset = left_block_offset
      self.right_block_offset = right_block_offset
      self.left_number = left_number
      self.right_number = right_number


global_uart_send_data = uart_send_data_t()

#______________________________________________________________________________________________________________________________
#感兴趣区配置
roi_area_width = 30
roi_area_color = (0, 0, 200)
roi_area_thickness = 2


left_roi = [40,40,roi_area_width,sensor.height()-40]
right_roi = [sensor.width()-roi_area_width-40,40,roi_area_width,sensor.height()-40]
top_roi = [0,10,sensor.width(),roi_area_width]
center_roi = [0,int(sensor.height()/2)-int(roi_area_width/2),sensor.width(),roi_area_width]
#bottom_roi = [0,sensor.height()- roi_area_width,sensor.width(),roi_area_width]

black_block_roi = [0,100,sensor.width(),100]

def draw_roi(img):
    img.draw_rectangle(left_roi, color = roi_area_color, thickness = roi_area_thickness, fill = False)
    img.draw_rectangle(right_roi, color = roi_area_color, thickness = roi_area_thickness, fill = False)
    img.draw_rectangle(top_roi, color = roi_area_color, thickness = roi_area_thickness, fill = False)
    img.draw_rectangle(center_roi, color = roi_area_color, thickness = roi_area_thickness, fill = False)
    img.draw_rectangle(black_block_roi, color = (0, 255, 0), thickness = roi_area_thickness, fill = False)
    return

#______________________________________________________________________________________________________________________________
#寻找色块区配置
red_threshold =[12, 68, 11, 63, 5, 81]
black_threshold =[0, 50, -24,-1, -18, 6]

class red_blob_location_t:
   def __init__( self, x=0, y=0,area = 0):
      self.x = x
      self.y = y
      self.area = area


#______________
#左部blob位置信息
left_blob_location = red_blob_location_t()
left_pixels_threshold = 20     #若一个色块的像素数小于 pixel_threshold ，则会被过滤掉。
left_area_threshold = 20       #若一个色块的边界框区域小于 area_threshold ，则会被过滤掉。
left_x_stride = 20               #是查找某色块时需要跳过的x像素的数量。找到色块后，直线填充算法将精确像素。 若已知色块较大，可增加 x_stride 来提高查找色块的速度。
left_y_stride = 20               #是查找某色块时需要跳过的y像素的数量。找到色块后，直线填充算法将精确像素。 若已知色块较大，可增加 y_stride 来提高查找色块的速度。

#______________
#右部blob位置信息
right_blob_location = red_blob_location_t()
right_pixels_threshold = 20     #若一个色块的像素数小于 pixel_threshold ，则会被过滤掉。
right_area_threshold = 20       #若一个色块的边界框区域小于 area_threshold ，则会被过滤掉。
right_x_stride = 20               #是查找某色块时需要跳过的x像素的数量。找到色块后，直线填充算法将精确像素。 若已知色块较大，可增加 x_stride 来提高查找色块的速度。
right_y_stride = 20               #是查找某色块时需要跳过的y像素的数量。找到色块后，直线填充算法将精确像素。 若已知色块较大，可增加 y_stride 来提高查找色块的速度。

#______________
#顶部blob位置信息
top_blob_location = red_blob_location_t()
top_pixels_threshold = 20     #若一个色块的像素数小于 pixel_threshold ，则会被过滤掉。
top_area_threshold = 20       #若一个色块的边界框区域小于 area_threshold ，则会被过滤掉。
top_x_stride = 15               #是查找某色块时需要跳过的x像素的数量。找到色块后，直线填充算法将精确像素。 若已知色块较大，可增加 x_stride 来提高查找色块的速度。
top_y_stride = 20               #是查找某色块时需要跳过的y像素的数量。找到色块后，直线填充算法将精确像素。 若已知色块较大，可增加 y_stride 来提高查找色块的速度。

#______________
#中部blob位置信息
center_blob_location = red_blob_location_t()
center_pixels_threshold = 20     #若一个色块的像素数小于 pixel_threshold ，则会被过滤掉。
center_area_threshold = 20       #若一个色块的边界框区域小于 area_threshold ，则会被过滤掉。
center_x_stride = 20               #是查找某色块时需要跳过的x像素的数量。找到色块后，直线填充算法将精确像素。 若已知色块较大，可增加 x_stride 来提高查找色块的速度。
center_y_stride = 20               #是查找某色块时需要跳过的y像素的数量。找到色块后，直线填充算法将精确像素。 若已知色块较大，可增加 y_stride 来提高查找色块的速度。


blob_location=[0,0]

def find_blob(img):

    global global_uart_send_data
    #top_blob_location.x = -1
    #top_blob_location.y = -1
    #center_blob_location.x = -1
    #center_blob_location.y = -1
    left_blob_location.x = -1
    left_blob_location.y = -1
    right_blob_location.x = -1
    right_blob_location.y = -1
    for blob in img.find_blobs([red_threshold], roi = left_roi, x_stride = left_x_stride, y_stride = left_y_stride, pixels_threshold=left_pixels_threshold, area_threshold=left_area_threshold, merge=False, margin=10):
        img.draw_rectangle(blob.rect())
        img.draw_cross(blob.cx(), blob.cy())
        left_blob_location.x = blob.cx()
        left_blob_location.y = blob.cy()
        left_blob_location.area = blob.area()

    for blob in img.find_blobs([red_threshold], roi = right_roi,x_stride = right_x_stride, y_stride = right_y_stride, pixels_threshold=right_pixels_threshold, area_threshold=right_area_threshold, merge=True, margin=10):
        img.draw_rectangle(blob.rect())
        img.draw_cross(blob.cx(), blob.cy())
        right_blob_location.x = blob.cx()
        right_blob_location.y = blob.cy()
        right_blob_location.area = blob.area()

    for blob in img.find_blobs([red_threshold], roi = top_roi,x_stride = top_x_stride, y_stride = top_y_stride, pixels_threshold=top_pixels_threshold, area_threshold=top_area_threshold, merge=True, margin=10):
        img.draw_rectangle(blob.rect())
        img.draw_cross(blob.cx(), blob.cy())
        #print("-------"+str(blob.area()))
        top_blob_location.x = blob.cx()
        top_blob_location.y = blob.cy()
        top_blob_location.area = blob.area()

    for blob in img.find_blobs([red_threshold], roi = center_roi,x_stride = center_x_stride, y_stride = center_y_stride, pixels_threshold=center_pixels_threshold, area_threshold=center_area_threshold, merge=True, margin=10):
        img.draw_rectangle(blob.rect())
        img.draw_cross(blob.cx(), blob.cy())
        center_blob_location.x = blob.cx()
        center_blob_location.y = blob.cy()
        center_blob_location.area = blob.area()
        #print(blob.pixels())


    for blob in img.find_blobs([black_threshold], roi = black_block_roi, pixels_threshold=30,merge=True,margin=50):
        img.draw_rectangle(blob.rect())
        img.draw_cross(blob.cx(), blob.cy())
        #print(blob.count())
        if(blob.count() >= 7):
            #print("tinche"+str(blob.count()))
            global_uart_send_data.recognition = 1
        else:
            global_uart_send_data.recognition = 0


    return

#______________________________________________________________________________________________________________________________
#色块连线区配置
lines_color = (0, 200, 0)
lines_thickness = 1

def draw_lines(img):
    img.draw_line(top_blob_location.x, top_blob_location.y, center_blob_location.x, center_blob_location.y, color = lines_color, thickness = lines_thickness)
    img.draw_line(left_blob_location.x, left_blob_location.y, right_blob_location.x, right_blob_location.y, color = lines_color, thickness = lines_thickness)
    return


#______________________________________________________________________________________________________________________________
#upacker python实现代码 ：https://github.com/aeo123/upacker/blob/master/python/upacker.py
#介绍请看这里：https://github.com/aeo123/upacker

class Upacker():
    def __init__(self):
        self._STX_L = 0x55
        self._MAX_PACK_SIZE = 1024 + 4 + 128
        self._calc = 0
        self._check = 0
        self._cnt = 0
        self._flen = 0
        self._state = 0
        self._data = bytearray()

    def _decode(self, d):
        if (self._state == 0 and d == self._STX_L):
            self._state = 1
            self._calc = self._STX_L
        elif self._state == 1:
            self._flen = d & 0xff
            self._calc ^= d & 0xff
            self._state = 2
        elif self._state == 2:
            self._flen |= (d & 0xff) << 8
            self._calc ^= d & 0x3F
            # 数据包超长得情况下直接丢包
            if ((self._flen & 0x3FFF) > self._MAX_PACK_SIZE):
                self._state = 0
                return -1
            else:
                self._data = bytearray(self._flen & 0x3FFF)
            self._state = 3
            self._cnt = 0
        elif self._state == 3:
            header_crc = ((d & 0x03) << 4) | ((self._flen & 0xC000) >> 12)
            self._check = d
            if (header_crc != (self._calc & 0X3C)):
                self._state = 0
                return -1
            self._state = 4
            self._flen &= 0x3FFF
        elif self._state == 4:
            self._data[self._cnt] = d
            self._cnt += 1
            self._calc ^= d
            if self._cnt == self._flen:
                self._state = 0
                #接收完，检查check
                if ((self._calc & 0xFC) == (self._check & 0XFC)):
                    return 0
                else:
                    return -1
        else:
            self._state = 0

        return 1

    # 解包
    def unpack(self, bytes_data, callback):
        ret = 0
        for i in bytes_data:
            ret = self._decode(i)
            if ret == 0:
                callback(self._data)
                if(is_upacker_debug):
                    print(self._data)
            elif ret == -1:
                # callback(None)
                print("err")

    # 打包
    def enpack(self, data):
        tmp = bytearray(4)
        tmp[0] = 0x55
        tmp[1] = len(data) & 0xff
        tmp[2] = (len(data) >> 8) & 0xff
        crc = tmp[0] ^ tmp[1] ^ tmp[2]
        tmp[2] |= (crc & 0x0c) << 4
        tmp[3] = 0x03 & (crc >> 4)

        for i in range(len(data)):
            crc ^= data[i]
        tmp[3] |= (crc & 0xfc)

        frame = struct.pack("BBBB%ds" % len(data), tmp[0], tmp[1], tmp[2],
                            tmp[3], data)
        #python3.5之前bytes数据没有hex()属性，所以修改了下面这个
        #print(frame.hex())
        if(is_upacker_debug):
            print(''.join(map(lambda x:('' if len(hex(x))>=4 else '/x0')+hex(x)[2:],frame)))

        return frame

#____________
#串口命令切换模式
uart_cmd_need_change_mode = 0

def print_hex(bytes):
    global work_mode,uart_cmd_need_change_mode

    hex_byte = [hex(i) for i in bytes]
    if is_upacker_recive_debug:
        print("-----"+" ".join(hex_byte))
    if bytes[0] == 0x00:
        work_mode = 0
    if bytes[0] == 0x01:
        work_mode = 1
    uart_cmd_need_change_mode = 1

#if __name__ == '__main__':
    #buf = bytearray([0x00, 0x01, 0x02,0x03,0x77])
    #pack = Upacker()
    #pkt = pack.enpack(buf)
    #pack.unpack(pkt, print_hex)

#______________________________________________________________________________________________________________________________
#upacker python实现代码结束



def upacker_init():
    pack = Upacker()

    return pack

yzh = 10

#______________________________________________________________________________________________________________________________
#发送数据到MCU，gd32是小端字节序
#pack各字母对应类型
#x   pad byte        no value            1
#c   char            string of length 1  1
#b   signed char     integer             1
#B   unsigned char   integer             1
#?   _Bool           bool                1
#h   short           integer             2
#H   unsigned short  integer             2
#i   int             integer             4
#I   unsigned int    integer or long     4
#l   long            integer             4
#L   unsigned long   long                4
#q   long long       long                8
#Q   unsilong long   long                8
#f   float           float               4
#d   double          float               8
#s   char[]          string              1
#p   char[]          string              1
#P   void *          long

def send_data_to_mcu(pack,global_uart_send_data):
    hex_data = ustruct.pack("<bbhhhhbb",                        #小端字节序
                   global_uart_send_data.work_mode,
                   global_uart_send_data.recognition,
                   global_uart_send_data.top_block_offset,          #以屏幕中线为0点
                   global_uart_send_data.center_block_offset,
                   global_uart_send_data.left_block_offset,          #以屏幕中线为0点
                   global_uart_send_data.right_block_offset,
                   global_uart_send_data.left_number,
                   global_uart_send_data.right_number,)
    pkg_data =  pack.enpack(hex_data)
    k210_uart.write(pkg_data)

#______________________________________________________________________________________________________________________________
#pack解包后的回调函数
#def data_callback(bytes):
    #hex_byte = [hex(i) for i in bytes]
    #print(" ".join(hex_byte))

#______________________________________________________________________________________________________________________________
#定时发送串口数据的定时器
#构造函数
# 定时器回调
pack = upacker_init()

def on_timer(timer):
    global work_mode

    global_uart_send_data.work_mode = work_mode
    if(top_blob_location.x != -1):
        global_uart_send_data.top_block_offset = top_blob_location.x-int(sensor.width()/2)
    else:
        global_uart_send_data.top_block_offset = 0

    if(center_blob_location.x != -1):
        global_uart_send_data.center_block_offset = center_blob_location.x-int(sensor.width()/2)
    else:
        global_uart_send_data.center_block_offset = 0

    if(left_blob_location.y != -1):
        global_uart_send_data.left_block_offset = left_blob_location.y-int(sensor.height()/2)
    else:
        global_uart_send_data.left_block_offset = 0

    if(right_blob_location.y != -1):
        global_uart_send_data.right_block_offset = right_blob_location.y-int(sensor.height()/2)
    else:
        global_uart_send_data.right_block_offset = 0



    global_uart_send_data.top_block_offset = top_blob_location.x-int(sensor.width()/2)
    global_uart_send_data.center_block_offset = center_blob_location.x-int(sensor.width()/2)


    send_data_to_mcu(pack,global_uart_send_data)

# 配置定时器0通道0
tim = Timer(Timer.TIMER0, Timer.CHANNEL0, mode=Timer.MODE_PERIODIC, period=10, unit=Timer.UNIT_MS, callback=on_timer, arg=on_timer, start=False, priority=1, div=0)
#定时发送串口数据
tim.start()


#______________________________________________________________________________________________________________________________
#数字识别配置区域
#anchors = [1.40625, 1.875, 1.09375, 1.1875, 1.25, 1.46875, 1.53125, 2.15625, 1.1875, 1.8125000000000002]
anchors = [1.7141, 2.4567, 1.8995, 2.8182, 1.9671, 2.9588, 2.1778, 3.0333, 2.3722, 2.7514]
#labels = ["1", "2", "3", "4", "5", "6", "7", "8"]
labels = ["7", "5", "3", "2", "1", "4", "6", "8"]

actual_number = [7,5,3,2,1,4,6,8]



KPU = kpu.load("/sd/yolov2.kmodel")
xy = [0,0]
kpu.init_yolo2(KPU,0.7,0.01,len(anchors)//2,anchors)

#______________________________________________________________________________________________________________________________
#主循环
while (True):
    gc.collect()
    img = sensor.snapshot()  # Take a picture and return the image.
    # img.draw_cross(sensor.width()//2, sensor.height()//2, color = (0, 255, 0), size = 10, thickness = 2)
    clock.tick()
    #手动切换
    if key_press_long ==1:
        key_press_long = 0
        #长按后切换K210工作模式
        if work_mode == 0:
            work_mode =1
            print("work mode to 1")
            sensor.set_windowing((224, 224))
        else:
            work_mode =0
            print("work mode to 0")
            img = img.resize(320, 240)
            sensor.set_windowing((320, 240))
    #GD32控制切换
    if uart_cmd_need_change_mode == 1:
        uart_cmd_need_change_mode = 0
        #串口命令来切换K210工作模式
        if work_mode == 1:
            print("work mode to 1")
            sensor.set_windowing((224, 224))
        else:
            print("work mode to 0")
            img = img.resize(320, 240)
            sensor.set_windowing((320, 240))

    if work_mode == 0:  # 巡线模式
        find_blob(img)
        draw_roi(img)
        draw_lines(img)
        if is_findflob_debug:
            print(clock.fps(), top_blob_location.x,center_blob_location.x, left_blob_location.y, right_blob_location.y)  # Note: CanMV Cam runs about half as fast when connected,int(top.x),int(top.y)
            print(clock.fps(), global_uart_send_data.top_block_offset,global_uart_send_data.center_block_offset, global_uart_send_data.left_block_offset, global_uart_send_data.right_block_offset)
            print(global_uart_send_data.recognition)
        fps = clock.fps()  # Update the FPS clock.
        img.draw_string(2, 2, ("%2.1ffps" % (fps)), color=(0, 128, 0), scale=2)
        lcd.display(img)

    else:  # 数字识别模式

        img = sensor.snapshot()  # Take a picture and return the image.
        code = kpu.run_yolo2(KPU, img)
        fps = clock.fps()  # Update the FPS clock.
        img.draw_string(2, 2, ("%2.1ffps" % (fps)), color=(0, 128, 0), scale=2)
        #print(clock.fps())
        if bool(code):
            for i in code:
                img = img.draw_rectangle(i.rect(), (0, 255, 0), 2, 0)
                xy[0] = i.x()
                xy[1] = (i.y() - 20)
                img = img.draw_string(xy[0], xy[1], (labels[i.classid()]), (0, 255, 0), scale=2)
                img = img.draw_string(xy[0], xy[1] + 24, '%.3f' % i.value(), color=(255, 0, 0), scale=2)
            if(code[0].x()<code[-1].x()):
                global_uart_send_data.left_number = actual_number[code[0].classid()]
                global_uart_send_data.right_number = actual_number[(code[-1].classid())]
            else:
                global_uart_send_data.left_number = actual_number[(code[-1].classid())]
                global_uart_send_data.right_number = actual_number[(code[0].classid())]
            #print(global_uart_send_data.left_number,global_uart_send_data.right_number)
        lcd.display(img)

    read_data = k210_uart.read()
    if read_data:
        read_str = pack.unpack(read_data, print_hex)
    lcd.display(img)  # Display image on lcd.
    if is_stack_heap_mem_debug:
        print("stack mem:"+str(gc.mem_free() / 1024)) # stack mem
        print("heap mem:"+str(utils.heap_free() / 1024)) # heap mem