CS 2450

CH 5 SLIDESHOW

• Powers of 2 through 2^13

• Binary Hex and decimal

• 2s comp

• Machine Language - Series of binary numbers that the computer can understand directly

• Assembly language - A human readable way to write code that the computer can easily turn into machine language

• High level language - More human readable way to write assembly language

• Executable Image - The machine language program after it has been finished and is ready to run

• Instruction - made up of opcode and operands

• Opcode - Operate, Data Movement, and Control - see opcode list

• Operands - Data to be used in the operation

• Program Counter(PC) - default to x3000

• Instruction Register(IR) - Instruction Pointed to by the PC is loaded into the IR

• PC is incremented at the same time as the loading of the IR

• Instruction is processed and executed

• Repeat until HALT

• LC3 flags - NZP - Negative, Zero, Positive

• Eight general purpose registers (R0-R7)

• Memory Address Register (MAR) - Holds the address of the memory unit to be written or read

• Memory Data Register (MDR) - Holds the value to transfer to or from memory

• Keyboard Data Register(KBDR) - Holds the ASCII character of the key after it has been typed

• Keyboard Status Register(KBSR) - Status info that lets the microprocessor know a key has been typed and is ready to read - last bit gets set to 1 when key is pressed

• Display Data Register (DDR) - Holds the ASCII character to display on the screen

• Display status register (DSR) - Status Info, Used to tell the display you are ready to write the character in DDR to the screen, last key is set to 0 until char is displayed,then = 1

• Process State Register(PSR) - Info about the current state of the current program

• Bitwise operations - applies the operation on each bit. Not Logical, Don’t use Boolean Arguments. AND & and NOT ~

• AND - Sign extended 1s do not act as 1s

• Addressing modes - PC-Relative, Indirect, Base+Offset

• PC-Relative - Uses current value of the PC, ld, st

• Indirect - address calculated from the PC finds the address we want - LDI,STI

• Base+Offset - Immediate Value is added to an address from a register

• Branch(BR) - Changes PC if designated NZP flags are hit

• Obtaining and Printing a character - GETC,OUT

• GETC - Puts the ASCII code of a keystroke in R0

• OUT - Prints the ASCII character in R0

• Trap Instruction - an instruction that allows calling of an operating system subroutine - GETC, OUT, PUTS, IN, PUTSP, HALT

•  Jumps - JSR,JSRR,JMP,RET

• Jump to Subroutine or Jump Save Return(JSR) - Stores return address in R7, jumps to subroutine - 11-bit pc relative addressing

• Jump to Subroutine(JSRR) - Return address saved in R7, Base register addressing 

• JMP - doesn't save return, base register addressing

• RET - Special form of JMP - base register is always R7

• PUTS - print string to the output - Address of string in R0

• IN - Get character from keyboard - Stores character and R0 and prints it to output

• PUTSP - same as PUTS but assumes two characters per word 

CH 6,7 SLIDESHOW

• Pseudo-ops - Assembler directives - .ORIG,.FILL,.BLKW,.STRINGZ,.END

• Labels - can be used as positions for jumping, branching,loading,storing - assembler calculates offsets using them

• .ORIG - specifies the starting address

• .FILL - initializes a memory location to a value

• .BLKW - reserves a block of memory locations 

• .STRINGZ - reserves a character memory as a string, null terminated

• .END - tells the assembler where the program ends

• Loops are commonly used with label TOP 

• When using a subroutine, always save and restore registers, store them somewhere at beginning, restore at end, don’t do anything with R7(return register)

• Logical or/ands can be replicated using multiple branches

• Be clean when LC3 coding

CH 2 SLIDESHOW

• Typically, 1 is 5v and 0 = 0v, 0 is not an absence of voltage, just a connection to the ground

• Biggest number using unsigned binary - 2^n-1

• Biggest using 2s comp - 2^(n-1)-1

• Smallest using unsigned - 0

• Smallest using 2s comp -  -2^(n-1)

• Sign extension

• Overflow

• Bit twiddling - AND,OR,XOR,right shift, left shift, NOT

• XOR - 1 true but not both

• Can clear certain bits with AND, ANDing with 11110000 clears right 4 bits

• Set bits with OR, ORing with 00001111 makes right 4 bits 1

• Using AND to only look at specific bits - ANDing with “00011000”(mask), returns only the 4th and 5th bit

• Bit vector 

• Base conversions

• Metric Prefixes

C SLIDESHOW

• Don’t use break, continue, or multiple returns

• Don’t use goto

• printf(“Hello\n”); - newline at end

• Preprocessor - processes directives, directives start with #, #include, #define

• #include - copies named file into source code buffer

• #define - replace any instance of a constant with a value specified in the entire source code buffer

• Compiler - converts code to assembly, tracks variable names in symbol table, tries to optimize code

• Linker - determines and inserts the addresses for any external code that is needed

• Three primitive types - int char double, no string

• Always use local variables and initialize them

• Declare constants with #define, constants have no type

• Operators are the same as java

• Precedence - order of operation

• Associativity - direction the operator works(++ is R to L),(>> is L to R)

• No boolean data type, boolean operators result in 1(true) or 0(false)(USE ==)

• & and | are bitwise ops, && and || are logical operators

• Printf specifiers: c-char,d|i-signint,e/E-scien,f-float,s-str,u-unsignint,x/X-unsignedint,p-pointer,n-nothing, lf - long float,

• Printf flags and width,precision and length ??

• Functions - no pub or priv, return types, parameters

• Pointers:int count = 5/ int ptr/ptr=&count/ptr=*ptr+1/printf(“%i”,count) = 6

• *ptr is only used to change the thing ptr is pointing at, &count is the address of count

• ptr = ptr + 1 increments the variable ptr is pointing to, ptr = ptr+1 increments what variable ptr is pointing to eg ct1 to ct2

• scanf(“%d”,&x); variable must be reference or ptr, input

• Scanf format - %[*][width][modifiers]type,reference

• Read past spaces - scanf(“%99[^\n]s”, test);

• Arrays - int grid[] = {1,2,3,4,5}; - cant tell length after creation, keep track

• Two dimensional arrays - int arr[][4] = {{1,2,3}, … } - need dimensions for all but first

• Dynamic arrays - void calloc(size_t num, size_t size) - reserves num bytes of memory, initializes memory to zero - void malloc(size_t size) reserves size bytes of memory, doesnt initialize memory to zero - dynamic arrays are used for random num

• Memory in c - text segment - Instructions, initialized data segment - global variables, static variables, string literals - heap - dynamic memory - stack - local variables, parameters, function return values, function arguments

• Strings in c - arrays of characters, must be null terminated

• strlen(const char *str) - gives the length of a string

• strncpy(a,b,9) - copies 9 characters from the string pointed to by a to b

• strncat(dest,src,n) appends the string point to by src to the end pointed to by dest

• strncmp(str1,str2,n) - compares the first n bytes of str1 and str2/return <0 = str1 is less than str2, > str1 > str2, = means equal

• strstr(*str1,*str2) finds first occurrence of str1 in str2

• strrchr(*str, char c) finds first occurrence of c in str

• strtok(*str,const char *delim) breaks str into tokens separated by delim, returns a pointer to next char after delim

• Structures - typedef struct { char last[size]; char first[size]; double gpa; int startYear; } student_t;

• student_t  s1, s2;/strncpy(s1.first,”Bill”, size);/strncpy(s1.last,”Gates”,size);/s1.gpa = 2.2;/s1.startYear = 1990;/s2=s1;

• Pointer to structure: student_t *sptr; sptr = &s1; sptr->gpa = 2.3;

• Functions need to be declared before use

• Stdlib.h - contains atoi - converts str to int/atof - str to double/rand - random number/malloc/calloc/free - deallocate memory/exit - normal program termination/abort - abnormal program termination

• Random numbers - rand() % 50

Circuits - ch3

• Source and ground

• Transistor - electronic switch - Metal Oxide Semiconductor - gate is the control - 1 = on = closed = conducting/ 0 = off = open = not conducting

• Resistance is required to prevent excessive heat

• N-type - requires 1 to conduct/p-type - requires 0 to conduct/p-type has the not circle

• Top half of circuit matters, bottom points down to ground.

• Inverter: makes 0 to 1 and 1 to 0

• NAND - Not(a and b)/ NOR - Not(Aor B)

• XOR - A or B but not both/ XNOR - 1 if both are the same

• Demorgans - distributing and/or inverts it

• Decoder - all combinations of inputs return a different output

• Multiplexer - mux - digital selector - chooses one of several inputs to appear on an output/takes inputs and switch that decides which bit goes through

• Larger muxes can produce multiple outputs 4x1 - 4 input/1output

• Adder - takes 2 4bit inputs and adds them

• Latch - stores 1s and 0s

• R-s latch - takes r/s and outs q / r=1,s=1, q doesnt change/r=1,s=0,q=1/r=0,s=1,q=0

• D-latch-modified r-s latch/single input with a write enable circuit, d/we=q: 0/0=nochange, 0/1=0, 1/0=nochange,1/1=1

• Four d-latches can store four bits, device storing multiple bits is a register

• IR is a 16 bit register - range of bits referred to with brackets - IR[15:12] - 15/14/13/12

• Combinational logic, takes inputs and determines output

• Sequential logic - takes previous outputs and inputs to determine output

• Finite State Machine - machine to generate all possible states, consists of finite num of states,inputs,outputs/explicit specifications of all transitions, and determinations of output

Ch4

• Von neumann architecture/princeton architecture, consists of: processing unit, memory,input,output,control unit. Main feature - program instructions and data share the same memory and use same pathways

• memory:MDR,MAR/Processing:ALU,TEMP/Control:PC,IR

• ALU - Arithmetic/Logic Unit - Math and logical operations, TEMP = registers

• BUS - transfer of data from source register to destination register requires each bit be connected by wire. Can only have one input active at a time

• Tristate buffer - 3 outputs, takes control and input(C/I/O):0/0/open - 0/1/open - 1/0/0 - 1/1/1

• Loading an instructing pulls from memory using the address given by the pc and places in IR. Address moves from PC to MAR, PC increments, look up address in MAR in memory and store value in MDR, Move value from MDR to IR

Ch5

• Ld - get PC, Get bottom 9 bits of IR, Add PC and Offset, Store in MAR, Look up MAR, store in MDR, put MDR in register

• ST - put address in MAR, put data to be stored in MDR, store MDR to memory

• JSR/JSRR - save PC to R7, change PC by offset

Ch 8,9,10

• I/O methods - special Instructions - Memory Mapped I/O

• Special Instructions - add instruction to ISA for in and out, limited # of instructions

• Memory Mapped - makes reading the keyboard and other inputs like reading from memory, writing to the display like to memory, makes some memory unusable

• Assign memory addresses to KBSR,KBDR,DSR,DDR,MCR

• Why interrupt, computers are really fast, wasteful to sit around. An interrupt has 2 parts: signal,service routine.

• Polling vs Interrupt: polling sits and waits on keyboard, interrupt does other things until keyboard says yes

• Assign priority so important tasks don’t get interrupted for less important tasks

• Interrupt has two parts - PSR: the PSR contains NZP flags, priority, and privilege bit(PR)

• Process switching: save the state of interrupted program/uses a supervisor stack/only used if PR is set in PSR

• Stack pointer - address of last item added/Overflow - trying to push too much in/underflow - trying to pop too much out
  Pushing in lc3 - have r6 be bottom, decrease by one and str from r6 into R0

• Popping - ldr r0 to r6, increment r6

• Checking for underflow - load r1 with end of stack, test if r1 = r6 with BR, jump to popfail

• Overflow - same idea but with top of stack