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实验了一下之前买的一个 Micro SD Card的模块【参考1】

SD卡是工作在 3.3v电压下面的，这个板子最主要的作用是实现5v转3.3v。我使用的是 Arduino Micro Pro.线路接法如下：

 

SD Card	Arduino Pro Micro
GND	GND
VCC	VCC(5V)
MISO	Pin14
MOSI	Pin16
SCK	Pin15
CS	Pin10

 

测试代码在 文件 -> 示例 –> SD –>CardInfo

/*
  SD card test

 This example shows how use the utility libraries on which the'
 SD library is based in order to get info about your SD card.
 Very useful for testing a card when you're not sure whether its working or not.

 The circuit:
  * SD card attached to SPI bus as follows:
 ** MOSI - pin 11 on Arduino Uno/Duemilanove/Diecimila
 ** MISO - pin 12 on Arduino Uno/Duemilanove/Diecimila
 ** CLK - pin 13 on Arduino Uno/Duemilanove/Diecimila
 ** CS - depends on your SD card shield or module.
 		Pin 4 used here for consistency with other Arduino examples


 created  28 Mar 2011
 by Limor Fried
 modified 9 Apr 2012
 by Tom Igoe
 */
// include the SD library:
#include <SPI.h>
#include <SD.h>

// set up variables using the SD utility library functions:
Sd2Card card;
SdVolume volume;
SdFile root;

// change this to match your SD shield or module;
// Arduino Ethernet shield: pin 4
// Adafruit SD shields and modules: pin 10
// Sparkfun SD shield: pin 8
const int chipSelect = 10;

void setup()
{
  // Open serial communications and wait for port to open:
  Serial.begin(9600);
  while (!Serial) {
    ; // wait for serial port to connect. Needed for Leonardo only
  }


  Serial.print("\nInitializing SD card...");
  // On the Ethernet Shield, CS is pin 4. It's set as an output by default.
  // Note that even if it's not used as the CS pin, the hardware SS pin
  // (10 on most Arduino boards, 53 on the Mega) must be left as an output
  // or the SD library functions will not work.
  pinMode(10, OUTPUT);     // change this to 53 on a mega


  // we'll use the initialization code from the utility libraries
  // since we're just testing if the card is working!
  if (!card.init(SPI_HALF_SPEED, chipSelect)) {
    Serial.println("initialization failed. Things to check:");
    Serial.println("* is a card is inserted?");
    Serial.println("* Is your wiring correct?");
    Serial.println("* did you change the chipSelect pin to match your shield or module?");
    return;
  } else {
    Serial.println("Wiring is correct and a card is present.");
  }

  // print the type of card
  Serial.print("\nCard type: ");
  switch (card.type()) {
    case SD_CARD_TYPE_SD1:
      Serial.println("SD1");
      break;
    case SD_CARD_TYPE_SD2:
      Serial.println("SD2");
      break;
    case SD_CARD_TYPE_SDHC:
      Serial.println("SDHC");
      break;
    default:
      Serial.println("Unknown");
  }

  // Now we will try to open the 'volume'/'partition' - it should be FAT16 or FAT32
  if (!volume.init(card)) {
    Serial.println("Could not find FAT16/FAT32 partition.\nMake sure you've formatted the card");
    return;
  }


  // print the type and size of the first FAT-type volume
  uint32_t volumesize;
  Serial.print("\nVolume type is FAT");
  Serial.println(volume.fatType(), DEC);
  Serial.println();

  volumesize = volume.blocksPerCluster();    // clusters are collections of blocks
  volumesize *= volume.clusterCount();       // we'll have a lot of clusters
  volumesize *= 512;                            // SD card blocks are always 512 bytes
  Serial.print("Volume size (bytes): ");
  Serial.println(volumesize);
  Serial.print("Volume size (Kbytes): ");
  volumesize /= 1024;
  Serial.println(volumesize);
  Serial.print("Volume size (Mbytes): ");
  volumesize /= 1024;
  Serial.println(volumesize);


  Serial.println("\nFiles found on the card (name, date and size in bytes): ");
  root.openRoot(volume);

  // list all files in the card with date and size
  root.ls(LS_R | LS_DATE | LS_SIZE);
}


void loop(void) {

}

 

运行结果

参考：
1． 淘宝店铺 赛宝电子
ArduinoSB配件 Micro SD卡模块 SPI接口 迷你TF卡读写(H5A2)

Arduino 默认使用了 Timer0 【参考1】，在 \arduino-1.6.3\hardware\arduino\avr\cores\arduino\wiring.c 有

#if defined(__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)
ISR(TIM0_OVF_vect)
#else
ISR(TIMER0_OVF_vect)
#endif
{
	// copy these to local variables so they can be stored in registers
	// (volatile variables must be read from memory on every access)
	unsigned long m = timer0_millis;
	unsigned char f = timer0_fract;

	m += MILLIS_INC;
	f += FRACT_INC;
	if (f >= FRACT_MAX) {
		f -= FRACT_MAX;
		m += 1;
	}

	timer0_fract = f;
	timer0_millis = m;
	timer0_overflow_count++;
}

 

简单的说，设置Timer0 1ms触发一次，然后其中的计数器会自动加1。同样的文件中还能看到millis( ) micros() 和delay() 函数都用到这个计数值。所以有如下结论：
1. 如果修改了Timer0的计时频率，这些函数都会受到影响
2. 如果你关闭了Timer0，那么这些函数都会失效
3. 如果你是编写中断服务，进入你的服务程序之后，关闭了中断，那么不可以使用这些函数

我们尝试修改这个文件，插入翻转pin的代码，可以看到，示波器上一直显示电平有变化

#if defined(__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)
ISR(TIM0_OVF_vect)
#else
ISR(TIMER0_OVF_vect)
#endif
{
	// copy these to local variables so they can be stored in registers
	// (volatile variables must be read from memory on every access)
	unsigned long m = timer0_millis;
	unsigned char f = timer0_fract;

	m += MILLIS_INC;
	f += FRACT_INC;
	if (f >= FRACT_MAX) {
		f -= FRACT_MAX;
		m += 1;
	}

	timer0_fract = f;
	timer0_millis = m;
	timer0_overflow_count++;
	//LABZ_Debug_Start
	digitalWrite(9,LOW);
	digitalWrite(9,HIGH);
	digitalWrite(9,LOW);	
	//LABZ_Debug_End
}

 

验证的代码非常简单：

void setup() {
  // put your setup code here, to run once:
  pinMode(9,OUTPUT);
}
void loop() {
 }

 

运行结果

放大一些看，间隔在1ms左右，就是Timer0触发一次的时间

同样的程序我们在主程序中使用noInterrupts关掉中断【参考2】，显示出来始终为低电平，因为Timer0被关掉了，ISR中的代码永远不会跑到。

void setup() {
  // put your setup code here, to run once:
  pinMode(9,OUTPUT);
  noInterrupts();
}

void loop() {
  // put your main code here, to run repeatedly:

}

 

运行结果，始终为低电平

某些时候我们只需要关闭Timer0的中断，可以用屏蔽溢出中断的方法，设置TOIE0为0即可。

#define OutPin 8
#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif

void setup() {
  // put your setup code here, to run once:
  pinMode(OutPin,OUTPUT);
  digitalWrite(OutPin,LOW);
  cbi (TIMSK0, TOIE0);
}

void loop() {
  // put your main code here, to run repeatedly:
  
}

 

运行结果和上图没差别，一直未低

此外还可以通过关闭Timer0的source的方法【参考3】来关闭Timer0.具体只要设置 CS00==CS01==CS02==0 即可。

#define OutPin 9

void setup() {
  // put your setup code here, to run once:
  pinMode(OutPin,OUTPUT);
  digitalWrite(OutPin,LOW);

}

void loop() {
  delay(1000);
  bitWrite(TCCR0B, CS00, 0);
  bitWrite(TCCR0B, CS01, 0);
  bitWrite(TCCR0B, CS02, 0);  
  delayMicroseconds(10000);
  digitalWrite(OutPin,HIGH);   
}

 

进入 loop函数之后 delay 1s 持续有中断产生，之后关闭了中断就出现一直为低的情况，接下来是10ms的delay，最后再拉高(这样只是为了让波形清晰可辩)。

放大一点可以看到，中间有间隔是10539ms.

特别注意：上述代码中，如果我将delayMicroseconds换成 Delay，那么看到的波形将会是一直为低。读者可以思考一下原因。

参考：
1. http://letsmakerobots.com/node/28278 Arduino 101: Timers and Interrupts

2.\arduino-1.6.3\hardware\arduino\avr\cores\arduino\Arduino.h
#define interrupts() sei()
#define noInterrupts() cli()

3. https://arduinodiy.wordpress.com/2012/02/28/timer-interrupts/
Clock Select bit description
CS12 CS11 CS10 Description
0 0 0 No clock source (Timer/Counter stopped)
0 0 1 clki/o/1 (No prescaling)
0 1 0 clki/o/8 (From Prescaler)
0 1 1 clki/o/64 (From Prescaler)
1 0 0 clki/o/256 (From Prescaler)
1 0 1 clki/o/1024 (From Prescaler)
1 1 0 External clock source on T1 pin. Clock on falling edge
1 1 1 External clock source on T1 pin. Clock on rising edge

最近在学习 Python，看了一本书<<与孩子一起学编程>>英文名是“Computer Programming for Kids and Other Beginners”,感觉挺有意思的。

书中推荐用 pygame 来编写游戏，我按照书上的程序打了一个滑雪者的小游戏。输入程序花了半小时，调试这个程序差不多花了2个小时。

最后调试通过的程序如下：

import pygame,sys,random

skier_images = ["skier_down.png","skier_right1.png",
                "skier_right2.png","skier_left2.png",
                "skier_left1.png"]

class SkierClass(pygame.sprite.Sprite):
    def __init__(self):
        pygame.sprite.Sprite.__init__(self)
        self.image = pygame.image.load("skier_down.png")
        self.rect = self.image.get_rect()
        self.rect.center = [320,100]
        self.angle =0

    def turn(self,direction):
        self.angle = self.angle + direction
        if self.angle < -2: self.angle = -2
        if self.angle >  2: self.angle = 2
        center = self.rect.center
        self.image = pygame.image.load(skier_images[self.angle])
        self.rect = self.image.get_rect()
        self.rect.center =center
        speed = [self.angle,6 - abs(self.angle) * 2]
        return speed

    def move(self,speed):
        self.rect.centerx = self.rect.centerx + speed[0]
        if self.rect.centerx < 20: self.rect.centerx = 20
        if self.rect.centerx > 620: self.rect.centerx =620

class ObstacleClass(pygame.sprite.Sprite):
    def __init__(self,image_file,location,type):
        pygame.sprite.Sprite.__init__(self)
        self.image_file = image_file
        self.image = pygame.image.load(image_file)
        self.location = location
        self.rect = self.image.get_rect()
        self.rect.center = location
        self.type =type
        self.passed =False

    def scroll(self, t_ptr):
        self.rect.centery = self.location[1] - t_ptr

def create_map(start, end):
        obstacles = pygame.sprite.Group()
        gates = pygame.sprite.Group()
        locations = []
        for i in range(10):
            row = random.randint(start,end)
            col = random.randint(0,9)
            location = [col * 64+20,row * 64 +20]
            if not (location in locations):
                locations.append(location)
            type = random.choice(["tree","flag"])
            if type == "tree": img = "skier_tree.png"
            elif type == "flag": img ="skier_flag.png"
            obstact = ObstacleClass(img,location,type)
            obstacles.add(obstact)
        return obstacles

def animate():
        screen.fill([255,255,255])
        pygame.display.update(obstacles.draw(screen))
        screen.blit(skier.image, skier.rect)
        screen.blit(score_text,[10,10])
        pygame.display.flip()

def updateObstacleGroup(map0,map1):
        obstacles = pygame.sprite.Group()
        for ob in map0: obstacles.add(ob)
        for ob in map1: obstacles.add(ob)
        return obstacles

pygame.init()
screen = pygame.display.set_mode([640,640])
clock = pygame.time.Clock()
skier = SkierClass()
speed = [0,6]
map_position =0
points=0;
map0 = create_map(20,29)
map1 = create_map(10,19)
activeMap =0;
obstacles = updateObstacleGroup(map0,map1)
font = pygame.font.Font(None,50)
        
while True:
    clock.tick(30)
    for event in pygame.event.get():
        if event.type == pygame.QUIT: sys.exit()
        if event.type == pygame.KEYDOWN:
            if event.key == pygame.K_LEFT:
                    speed = skier.turn(-1)
            elif event.key == pygame.K_RIGHT:
                    speed = skier.turn(1)
    skier.move(speed)
    map_position+=speed[1]

    if map_position >= 640 and activeMap == 0:
            activeMap = 1
            map0 = create_map(20,29)
            obstacles = updateObstacleGroup(map0,map1)
    if map_position>= 1280 and activeMap == 1:
            activeMap = 0
            for ob in map0:
                ob.location[1] = ob.location[1] -1280
            map_position = map_position - 1280
            map1 = create_map(10,19)
            obstacles = updateObstacleGroup(map0,map1)
            
    for obstacle in obstacles:
            obstacle.scroll(map_position)
    hit = pygame.sprite.spritecollide(skier,obstacles,False)
    if hit:
        if hit[0].type == "tree" and not hit[0].passed:
            points = points -100
            skier.image = pygame.image.load("skier_crash.png")
            animate()
            pygame.time.delay(1000)
            skier.image = pygame.image.load("skier_down.png")
            skier.angle = 0
            speed =[0,6]
            hit[0].passed = True
        elif hit[0].type == "flag" and not hit[0].passed:
            points +=10
            obstacles.remove(hit[0])
    score_text = font.render("Score: "+str(points),1,(0,0,0))
    animate()

 

运行结果：

如果你也恰好阅读这本书，遇到同样的问题，建议你参考上面的程序，此外需要特别注意的是 Python 使用缩进之类的来表示上下文之间的隶属关系。如果你的程序遇到莫名其妙的错误，请检查是不是缩进搞错了。比如：

class x:
def func1
def func2

这样，func2 是 x 的一个方法了，如果你在其他地方试图直接调用 func2 就会出现未定 func2 的问题。我因为这样的事情被卡了很久。

最后放上完整的代码（包括官方网站下载到的官方板的源程序），如果你调试不过，最后还可以用beyond compare 这样的对比工具找到原因。

skier