Question

Write RISC-V assembly code for placing the following immediate constants

in register s7. Use a minimum number of instructions. PLEASE EXPLAIN each and every single step that you used to arrive at the solution! Thank you!
a) 29
b) -214
c) 0xEEEEEFAB
d) 0xEDCBA123

Answer 1

The RISC-V assembly code to load immediate constants into register s7 requires the use of 'addi' for small values and 'lui' followed by 'addi' for larger 32-bit constants.

Step-by-step explanation:

The student's task involves writing RISC-V assembly code to load immediate constants into a specific register, which in this case is s7. Here is how you can do it:

1. To load the immediate value 29 into s7, a simple addi instruction suffices, because the value is small enough to fit into the immediate field:
2. addi s7, zero, 29
3. To load the negative value -214 into s7, use addi with the immediate value directly, as it falls within the range of a 12-bit signed immediate:
4. addi s7, zero, -214
5. To load the 32-bit constant 0xEEEEEFAB into s7, you will need to use a pair of instructions since the value is too large for a single immediate. First, use lui to load the upper 20 bits, then use addi to set the lower 12 bits:
6. lui s7, 0xEEEEF
7. 
   
8. addi s7, s7, -341
9. Similarly, to load the constant 0xEDCBA123, use lui and addi in combination:
10. lui s7, 0xEDCBA
11. 
    
12. addi s7, s7, 291

For constants c) and d), note that the addi instruction is used to add a signed 12-bit immediate to a register, and thus the lower 12 bits in 0xEEEEEFAB are interpreted as signed while calculating to -341 and the lower 12 bits of 0xEDCBA123 are 291 once signed extension is considered.