John Reed

372 uarchhw

03 June 2005

Here is my microcode for the ijvm for a shift right n opcode ISHR that’s shifts the second from the top word of the stack by the top word of the stacks number, represented by the 5 least significant bits, right and propagates the sign bit.

ishr1 OPC = 1 //initialize H to 1

ishr2 OPC = OPC << 8 //shift left 8 100000000

ishr3 OPC = OPC >> 1 //shift right 1 010000000

ishr4 OPC = OPC >> 1 //shift right 1 001000000

ishr5 OPC = OPC >> 1 //shift right 1 000100000

ishr6 OPC = OPC - 1 //subtract 1 000011111

ishr7 H = OPC //copy the bitmask to H

ishr8 MAR = SP = SP - 1; rd //Read in second from top word on stack

ishr9 TOS = H AND TOS //apply the bitmask and save it in TOS

ishr10 H = -1 //initialize H to -1

ishr11 H = H >> 1 //shift right 1 011111....

ishr12 H = H + 1 //add 1 100000....

ishr13 OPC = H AND MDR //save the highest order bit

ishr14 H = MDR //get the word to shift

ishr15 Z = TOS; if (Z) goto ishr19; else goto ishr16

ishr16 H = H >> 1 //shift the word 1 bit right

ishr17 TOS = TOS - 1; goto ishr15 //loop until counter is 0

ishr18 H = H OR OPC //add the highest order bit back in

ishr19 TOS = MDR = H; wr; goto Main1 //save the result to the top of the stack

Here is my ijvm code to print out the ascii code for a character typed in.

.main

.var

input

.end-var

L1: IN // request character input from memory

DUP // duplicate top of stack (inputted char) for comparing

BIPUSH 0x0 // push 0x0 for comparison

IF_ICMPEQ L2 // if no characters are available for input, loop

DUP // make a copy for second hex

ISTORE input //because return doesn’t go to right place for stack use a variable

BIPUSH 0x04

ISHR //shift over 4 to get the first hex

INVOKEVIRTUAL findascii //get the first hex

OUT // print the hex

ILOAD input

INVOKEVIRTUAL findascii //get the second hex

OUT // print the hex

GOTO L1 // loop back to beginning of program

L2: POP // No key has been pushed, so clear the stack,

GOTO L1 // and start over

.end-main

//return the ascii value for the hex value of the 4 least significant bits

.method findascii(n)

.var

temp

.end-var

ILOAD n // load the value to convert

BIPUSH 0xF

IAND // mask off last 4 bits

BIPUSH 0x30 //offset to number 0

IADD

ISTORE temp

BIPUSH 0x39 //ascii value of 9

ILOAD temp

ISUB //check if number is greater than 9

IFLT AL //check if we need to print a letter

ILOAD temp

GOTO MO

AL: BIPUSH 0x7

ILOAD temp

IADD //if it is a letter we need to print add 7 to offset of A

MO: IRETURN

.end-method