Yalamanchili
GEORGIA INSTITUTE OF TECHNOLOGY
School of Electrical and Computer Engineering
ECE 2030: Sections C & D
Spring 2008
Assignment #5
No late assignments will be accepted.
This assignment has two parts with two due dates.
Part I: Due date: Monday, April 7th, 2008, midnight (not Sunday night)
electronically to your TA.
Microcode
1. Write the microcode to compute the expression R1 = [(R4-(3*R6))/4] + 1024
2. Write the microcode to reverse the order of the bytes stored at memory location 0x1024
and store the result in memory location 0x1028.
3. The word at memory location 0x1000 has the address of the first word of an array of four
words. Compute the sum of the elements of the array and have this sum stored in register
R5.
SPIM
A string was encrypted with the following sequence of operations.
For each character (byte) of the string:
1. Add 4 to the byte
2. XOR the result with the corresponding byte of a key (provided below)
3. Subtract 2 from the result
Repeat for next byte until end of string.
The resulting string after encryption was “Y@XCQLe” (Does not include the quotation
marks). The key used was “*+-26%#” (Does not include the quotation marks). Your task is to
write a SPIM program that uses the resulting string and key as input and produces the
decrypted string and store the decrypted string back in the data segment. Print the decrypted
string to the screen. Code to print a string can be found in the example code provided for
Assignment 4.
Do this by reversing the operations for encryption. You can store the input and output strings
in memory using data directives as you did in Assignment 4. Note: To decrypt you have to
perform operations above in reverse order and perform the inverse operation in each step, i.e.,
