October 4th:
Circular redundant check code
Several basic concepts
1, polynomial and binary digital
The number of polynomial and binary has a direct correspondence: the highest bit of the maximum number of binary numbers of X. The following points correspond to the power of the polynomial, there is this power sub-item corresponding to 1, no this power sub-item corresponds to 0. It can be seen that the maximum power of X is R, converted into a corresponding number of binarys with R 1.
Polynomials include generating polynomial g (x) and information polynomial C (x).
If the polynomial is g (x) = x4 x3 x 1, it can be converted to binary digital 11011.
The transmission information bit 1111 can be converted to the data polynomial to c (x) = x3 x2 x 1.
2, generate polynomial
It is an agreement between the acceptor and the sender, that is, a binary number, this number is always unchanged throughout the transmission process.
In the sender, the generated polynomial is used to modify the information, and the check code is generated. In the acceptor utilizes the generated polynomial, the encoded polynomial is used to detect and determine the error location.
The following conditions should be met:
A. The highest level and lowest bit of the polynomial must be 1.
B. When an error occurs when an error occurs when the information (CRC code) occurs, the remainder should not be 0 after being generated.
C, when a different bit is wrong, the remainder should be different.
D. Continue to the remainder is divided, and the remainder cycle should be made.
(The exam is mainly taken below the following operations)
3, mode 2]
The mold 2 is similar to the arithmetic division, but the result of each bit is not affected by the other bits, ie the borrow is not borrowed. So actually is different or. (It is actually a subtraction of not carry: 0-1 = 1 1-1 = 0 0-0 = 0 So 1001/1010 = 0011 ourselves) and then shift the displacement to do the next one of the mold 2 minus. Proceed as follows:
A. Use divisions to do only several of the modified numbers 2 minus 2, no borrowing.
b, divide one bit right, and if the highest bit is 1, the merchant is 1, and the remainder is 2 minus. If the highest bit is 0, the business is 0, the divisor continues to move right.
c, the number of bits that have been restored is less than the division, the remainder is the final number.
[Example] 1111000 divided by 1101:
1011 --- Business
----
1111000 ----- Detailed
1101 ---- divisor
----
010000
1101
----
01010
1101
----
111 ----余
October 5th:
Computer Architecture: 1.1 Several Important Concept Clock Cycles: Time Interval Instruction Peridation Period: Central Processor Executes Instructions (including Address) CPU Period (Machine Period): The shortest time read from memory (Consist of several clock cycles). Interrupt Response Time: The time of protecting the site (off interrupt to open interrupt). Interrupt processing time: time from the response to the on-site recovery. 1.2 Peripheral 1.2.1 Peripheral Identification Independent Additive Method Unified Add Identification Method 1.2.1 Access Procedure Query Method Interrupt DMA Channel Way 1.3 Interrupt 1.4DMA
