Program to Create A Simplified Version Of PrintF In ARM Assembly Language Assignment Solution

Instructions

Requirements and Specifications

• The address of the format string is specified in R1, the address of the values is specified in R2 — if you use other registers, you program will fail in the pipeline. Likewise, you must not add in code before the label printf in the skeleton file, 01-printf.s, or your program will not execute correctly. You may however (and probably should) modify the format strings and sequence of values to ensure your program works correctly with different input.
• Your program will need to loop through every character of the format string, and print out thecharacters (using SWI 0), unless the character is a percent (‘%’) character.
• Your program should stop looping when it reaches a null character in the format string, (i.e. when the byte read from memory has the literal value of zero (not the ASCII code for the character representing the digit zero). You can find this by comparing with #0.
• The format string is made up of characters that are one byte long, you will need to use LDRB toaccess these. The values are all 32-bits (four bytes) long, you will need to use LDR to access these.
• If your program encounters a conversion specifier, (i.e. you read a ‘%’ character from the format string), then your program should fetch the next byte of the format string from memory. Then based on the value of this character, your program should:
• If the conversion specifier is %%, then your program should print out a single percent character. The value of R2 should not be updated.
• If the conversion specifier is %c, then your program should read the 32-bit value from the address currently specified in R2. Your program should treat the value read as an ASCII character and print it out using SWI 0. The value of R2 should be updated to contain the address of the next value in the sequence.
• If the conversion specifier is %d, then your program should read the 32-bit value from the address currently specified in R2. Your program should treat the value read as an unsignedinteger value and print it out using SWI 4. The value of R2 should be updated to contain the address of the next value in the sequence.
• If the conversion specifier is %s, then your program should read the 32-bit value from the address currently specified in R2. Your program should treat the value read as containing the address of a null-terminated string and print it out using SWI 3. The value of R2 should be updated to contain the address of the next value in the sequence.
• Invalid conversion specifiers should print nothing out.
• Bear in mind that each value in the sequence of values is 4 bytes long.
• It can be instructive to consider this program as being formed from two parts. One part of the program is stepping through each character of the format string deciding what needs to be printed (the character, or a value — and for each value, what type of value). The other part of the program is fetching the value from the sequence of values and printing it out based on the type specified in the string. I’d suggest working on the two parts of the program separately, first get the program stepping through the format string printing out dummy values, then when you are confident that part is working, move onto writing the code to read the actual values from memory.