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equation:

abs(new_reading - calibrating_reading)/calibrated_reading * 100 = similarity




now using our numbers:


grey floor = (108 - 95)/95 * 100 = 13.7% different


white line = (108 - 112)/112 * 100= 3.6% different




compare: white line < grey floor


therefore the sensor sees a white line

if you wanted three different colors it would look something like this:

A third integer promotion rule that is often overlooked concerns
expressions that contain both signed and unsigned integers. In this case,
signed integers are promoted to unsigned integers. Although this makes
sense, it can present problems in our eight-bit environment, where the
unsigned integer rules. For example:

void demo(void)

{

UINT a = 6;

INT b = -20;

(a+b > 6) ?
puts(“More than 6”) : puts(“Less than or
equal to 6”);

}

If you run this program, you may be surprised to find that the output is
“More than 6.”

• Check your compiler documentation. It may allow you to specify
via a command line switch that enumerated types be put into the smallest
possible data type. The downside is, of course, compiler-dependant code

• Accept the inefficiency as an acceptable trade-off for
readability

• Dispense with
enumerated types and resort to lists of manifest
constants

many compiler vendors have
seen the light, and allow you to disable the ANSI automatic integer
promotion rules. However, you’re then stuck with compiler-dependant
code.

Alternatively, you can resort to very clumsy casting, and hope that
the compiler’s optimizer works out what you really want to do. The
extent of the casting required seems to vary among compiler vendors. As a
result, I tend to go overboard:

res = (CHAR)((CHAR)a
+ (CHAR)b);

one needs to use the following declaration:

volatile UCHAR status_register _at_ 0xE000;

status_register =
XBYTE[0xE000];

Here, however, examination of the XBYTE macro shows that volatile is
assumed:

#define XBYTE ((unsigned char volatile xdata*) 0)

Use of assert

The assert() macro is commonly used on PC platforms, but almost never used
on small embedded systems. There are several reasons for this:

• Many reputable compiler vendors don’t bother to supply
an assert macro

• Vendors that do supply the macro often provide it in an almost
useless form

• Most embedded systems don’t support a stderr
to which
the error may be printed

Assert #1

This example assumes that you have no spare RAM, no spare port pins, and
virtually no ROM to spare. In this case, assert.h becomes:

#ifndef assert_h

#define assert_h

#ifndef NDEBUG

#define
assert(expr) \

if (expr) {\

while (1);\

}

#else

#define assert(expr)

#endif

#endif

Assert #2

This case is the same as assert #1, except that in #2 you have a spare port
pin on the microcontroller to
which an error LED is attached. This LED is
lit if an error occurs, thus giving you instant feedback that an assertion
has failed. Assert.h now becomes:

#ifndef assert_h

#define assert_h

#define ERROR_LED_ON() /* Put
expression for turning LED on here */

#define INTERRUPTS_OFF() /* Put
expression for interrupts off here */

#ifndef NDEBUG

#define
assert(expr) \

if (expr) {\

ERROR_LED_ON();\

INTERRUPTS_OFF();\

while (1);\

}

#else

#define
assert(expr)

#endif

#endif

Assert #3

This example builds on assert #2. But in this case, we have sufficient RAM
to define an error message buffer, into which the assert macro can
sprintf() the exact failure. While debugging on an ICE, if a permanent
watch point is associated with this buffer, then breaking the ICE will give
you instant information on where the failure occurred. Assert.h for this
case becomes:

#ifndef assert_h

#define assert_h

#define ERROR_LED_ON() /* Put
expression for
turning LED on here */

#define INTERRUPTS_OFF()/* Put
expression for interrupts off here */

#ifndef NDEBUG

extern
char error_buf[80];

#define assert(expr) \

if (expr) {\

ERROR_LED_ON();\

INTERRUPTS_OFF();\

sprintf(error_buf,”Assert failed: “ #expr “ (file %s
line %d)\n”, __FILE__, (int) __LINE__ );\

while (1);\

}

#else

#define assert(expr)

#endif

#endif

Recursion

Recursion is a wonderful technique that solves certain problems in an
elegant manner. It has no place on an eight-bit microcontroller.

Variable length argument lists

You should avoid variable length argument lists because they too rely on a
stack-based approach to passing variables. What about sprintf() and its
cousins, you all cry? Well, if possible, you should consider avoiding the
use of these library functions.

An easy way to build in volatility into each UART is to write the typedef as:

typedef struct UART volatile UART;

A better way to define UART as an inherently volatile type is to fold the entire struct definition into the typedef and eliminate the structure tag, as in:

typedef struct /* no tag */
{
special_register ULCON;
special_register UCON;
// etc.
} volatile UART;

Alternatively, you can declare every member of the struct to be volatile, as in:
typedef struct UART UART;

struct UART
{
special_register volatile ULCON;
special_register volatile UCON;
// etc.
};

The most obvious way to do that is define special_register as a volatile type, as in:

typedef uint32_t volatile special_register;

I recommend defining a nonvolatile type for the shadow register and a volatile version of the shadow register type for the corresponding device register, as in:

typedef uint32_t shadow_register;
typedef shadow_register volatile 
special_register;

提高硬件可靠性的考虑:

.尽量采用片内晶体、采用低频率的系统时钟、振荡电路的输出小幅度。



.选择合适的启动延时参数



.使用BOD、片内的看门狗



.合理休眠方式的使用



.不用I/O口设定输出低电平



.利用内部的EEProm和寄存器MCUCSR判断复位标志，进行不同的处理

通信接口的编写应尽量

.采用中断+缓冲区，



.分层+结构化设计，



.尽量不使用轮循方式(降低AVR的效率)。参见URAT（RS232）驱动+中间层软件示例。

Set one straightened paper clip aside, you will use it at the
end. Bend the two tips of one of the two paper clips as shown.

Put it in through the fuse clip like this, but make sure the
notch in the fuse clip is facing out. (The clip has one edge bent inwards. This
is the part that has to face outwards). Study this next picture closely.

From the position above, bend the paper clip up and then
around the lead of the fuse clip as in the next picture.

Bend the paper clip under the fuse clip...

then up and over the fuse clip:

then around its other lead and you're almost done with the
first fuse clip.

First clip -- wire is on the RIGHT side of the fuse clip
leads...

Second Clip -- wire is on the LEFT side of the fuse clip
leads... But remember to make sure the notch in the fuse clip is facing out.
(The clip has one edge bent inwards. This is the part that has to face
outwards). 

Follow all the steps above with the second clip and you get
this:

The infrared protocol includes the following capabilities:






• 
  
  Check that a Cricket is present and ready for other commands.
  
• 
  Write a byte to the Cricket's EEPROM.
  
• 
  Read a byte from the Cricket's memory.
  
• 
  Begin program execution from a particular memory address.

ab, onfor 20

There is also a free-running timer, which keeps track of elapsed
time even when the Cricket is doing other things.

global [cats dogs]

creates two globals, named cats and
dogs. Additionally, two global-setting primitives,
setcats and setdogs, are instantiated.