# Lab2: RISC-V RV32I[MA] emulator with ELF support
**Tower of Hanoi** done by 黃瀚群

This is my C code

void TowerOfHanoi(int n, int A, int B, int C ){
        volatile char* tx = (volatile char*) 0x40002000;
        //volatile char* move= (volatile char*) 0x40002000;

        char* Hanoi= "Move Disk ";
        char* To = " To ";
        if( n = 1)
        {       *tx = A + '0';
                *tx = *To;
                *tx = B + '0';
                char *tmp = Hanoi;
                while(*tmp){
                        *tx = *tmp;
                        tmp++;
                }
                return;
        }
        TowerOfHanoi(n-1, A, C ,B);
        *tx = A + '0';
        *tx = *To;
        *tx = B + '0';
        char *tmp = Hanoi;
                while(*tmp){
                        *tx = *tmp;
                        tmp++;
        }
        TowerOfHanoi(n-1, C, B, A);

}
int _start()
{
        volatile int n = 3;
        volatile int A = 1;
        volatile int B = 2;
        volatile int C = 3;

        TowerOfHanoi(n, A, B, C);

        return 0;
}

After execution of the above C code. I get this assembly code.

 surajubuntu@surajubuntu:~/rv32emu$ riscv-none-embed-objdump -d test1

test1:     file format elf32-littleriscv


Disassembly of section .text:

00010054 <TowerOfHanoi>:
   10054:	03058593          	addi	a1,a1,48
   10058:	400027b7          	lui	a5,0x40002
   1005c:	0ff5f593          	andi	a1,a1,255
   10060:	00b78023          	sb	a1,0(a5) # 40002000 <__global_pointer$+0x3fff06dc>
   10064:	02000713          	li	a4,32
   10068:	03060613          	addi	a2,a2,48
   1006c:	00e78023          	sb	a4,0(a5)
   10070:	0ff67613          	andi	a2,a2,255
   10074:	00c78023          	sb	a2,0(a5)
   10078:	000107b7          	lui	a5,0x10
   1007c:	11878793          	addi	a5,a5,280 # 10118 <_start+0x7c>
   10080:	04d00713          	li	a4,77
   10084:	400026b7          	lui	a3,0x40002
   10088:	00e68023          	sb	a4,0(a3) # 40002000 <__global_pointer$+0x3fff06dc>
   1008c:	00178793          	addi	a5,a5,1
   10090:	0007c703          	lbu	a4,0(a5)
   10094:	fe071ae3          	bnez	a4,10088 <TowerOfHanoi+0x34>
   10098:	00008067          	ret

0001009c <_start>:
   1009c:	ff010113          	addi	sp,sp,-16
   100a0:	00300793          	li	a5,3
   100a4:	00f12023          	sw	a5,0(sp)
   100a8:	00100713          	li	a4,1
   100ac:	00e12223          	sw	a4,4(sp)
   100b0:	00200713          	li	a4,2
   100b4:	00e12423          	sw	a4,8(sp)
   100b8:	00f12623          	sw	a5,12(sp)
   100bc:	00012783          	lw	a5,0(sp)
   100c0:	00412703          	lw	a4,4(sp)
   100c4:	00812783          	lw	a5,8(sp)
   100c8:	400026b7          	lui	a3,0x40002
   100cc:	03070713          	addi	a4,a4,48
   100d0:	0ff77713          	andi	a4,a4,255
   100d4:	00c12603          	lw	a2,12(sp)
   100d8:	03078793          	addi	a5,a5,48
   100dc:	00e68023          	sb	a4,0(a3) # 40002000 <__global_pointer$+0x3fff06dc>
   100e0:	02000713          	li	a4,32
   100e4:	00e68023          	sb	a4,0(a3)
   100e8:	0ff7f793          	andi	a5,a5,255
   100ec:	00f68023          	sb	a5,0(a3)
   100f0:	000107b7          	lui	a5,0x10
   100f4:	11878793          	addi	a5,a5,280 # 10118 <_start+0x7c>
   100f8:	04d00713          	li	a4,77
   100fc:	00e68023          	sb	a4,0(a3)
   10100:	00178793          	addi	a5,a5,1
   10104:	0007c703          	lbu	a4,0(a5)
   10108:	fe071ae3          	bnez	a4,100fc <_start+0x60>
   1010c:	00000513          	li	a0,0
   10110:	01010113          	addi	sp,sp,16
   10114:	00008067          	ret

Readelf

surajubuntu@surajubuntu:~/rv32emu$ riscv-none-embed-readelf -h test1
ELF Header:
  Magic:   7f 45 4c 46 01 01 01 00 00 00 00 00 00 00 00 00 
  Class:                             ELF32
  Data:                              2's complement, little endian
  Version:                           1 (current)
  OS/ABI:                            UNIX - System V
  ABI Version:                       0
  Type:                              EXEC (Executable file)
  Machine:                           RISC-V
  Version:                           0x1
  Entry point address:               0x1009c
  Start of program headers:          52 (bytes into file)
  Start of section headers:          728 (bytes into file)
  Flags:                             0x0
  Size of this header:               52 (bytes)
  Size of program headers:           32 (bytes)
  Number of program headers:         1
  Size of section headers:           40 (bytes)
  Number of section headers:         7
  Section header string table index: 6

size:

surajubuntu@surajubuntu:~/rv32emu$ riscv-none-embed-size test1
   text	   data	    bss	    dec	    hex	filename
    208	      0	      0	    208	     d0	test1

- Difference between -O3 and -Os argument

surajubuntu@surajubuntu:~/rv32emu$ riscv-none-embed-gcc -O3 -nostdlib test1.c -o t1
surajubuntu@surajubuntu:~/rv32emu$ ./emu-rv32i t1

>>> Execution time: 212 ns
>>> Instruction count: 1 (IPS=4716981)
>>> Jumps: 0 (0.00%) - 0 forwards, 0 backwards
>>> Branching T=0 (-nan%) F=0 (-nan%)

surajubuntu@surajubuntu:~/rv32emu$ riscv-none-embed-gcc -Os -nostdlib test1.c -o t2
surajubuntu@surajubuntu:~/rv32emu$ ./emu-rv32i t2

>>> Execution time: 298 ns
>>> Instruction count: 1 (IPS=3355704)
>>> Jumps: 0 (0.00%) - 0 forwards, 0 backwards
>>> Branching T=0 (-nan%) F=0 (-nan%)