Task 1. Assume you are dealing with a 32 bit microprocessor that accesses memory in words (i.e. 32 bits) at a time, while memory is addressed bytewise. You should store strings in memory in an aligned way. You should use as little memory as possible without becoming unaligned.

• Sketch the memory of the specified machine, with the string "S" stored starting at an address above or equal to 2012 (decimal).
• Sketch the memory of the specified machine, with the string "S" stored starting at an address above or equal to 2013 (decimal).
• Sketch the memory of the specified machine, with the strings "Sunshine", "Rainy", "Joy", and "Pain", stored starting at an address above or equal to 2012 (decimal).
• Sketch the memory of the specified machine, with the strings "Sunshine", "Rainy", "Joy", and "Pain", stored starting at an address above or equal to 2013 (decimal).

Task 2. Download and install the RARS RISC-V simulator and familiarise yourself with using RARS.

Task 3. Familiarise yourself with the RISC-V processor and assembler language. Here are some links you may find helpful (no need to read all).

• Short RISC-V Assembler Reference.
• Advanced material (going way beyond what's needed in our course):
  • RISC-V homepage.
  • RISC-V GitHub.
  • The RISC-V Instruction Set Manual. Don't worry, you don't have to study this in detail, but might be useful if you want to look up fine points.

Task 4. Write the following programs in RISC-V assembler language.

• A program that counts the content of register t1 down to 0 and then terminates.
• A program that counts the content of a memory cell down to 0 and then terminates. They following (pseudo) commands might be useful:
  • The (pseudo) command la reg mem loads the label mem into the register reg.
  • The (pseudo) command sw reg1 mem reg2 stores the content of reg1 in the memory cell addressed by the label mem, using reg2 as temporary.
• A program that copies 100 Bytes from one region of memory to another.
• A program that copies N words from the memory region starting at A to the memory region starting at B. Note that the source and target regions may overlap, or incrementing a register may lead to wrapping of the register back to 0. Is that a problem for your program?
• Write a program that computes (2+3)*4 and leaves the result on top of the stack (remember that the stack pointer should always point to the first free memory cell that's above the top of the stack, if the stack grows downwards).

I recommend that you try out your RISC-V programs in RARS (step mode) and observe how the execution changes registers and memory.

Task 5. You were asked in last week's tutorial how to simulate an accumulator machine on a register machine. The RISC-V assembly language does not contain push and pop operations. RISC-V also does not allow binary operations (e.g. addition and comparison) to fetch arguments from the stack. How can we simulate an accumulator machine in RISC-V? Does the simulation work for the register machines with limited registers we saw in lecture 8 (see here)?

Recall that we discussed a two-phase strategy for register machines with limited registers (see here). Is this strategy still working if you simulate accumulator machines in a register machine with limited registers? How?