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# Cant write cant add 48s3 s2 32s3 2004 morgan kaufman

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Unformatted text preview: emember arithmetic operands are registers, not memory! Can’t write: Can’t add 48(\$s3), \$s2, 32(\$s3) 2004 © Morgan Kaufman Publishers Spring 2013, Jan 25 . . . Spring ELEC 5200-001/6200-001 Lecture 3 14 Our First Example Can we figure out the code of subroutine? swap(int v, int k); { int temp; temp = v[k] v[k] = v[k+1]; v[k+1] = temp; } swap: sll \$2, add \$2, lw \$15, lw \$16, sw \$16, sw \$15, jr \$31 \$5, 2 \$4, \$2 0(\$2) 4(\$2) 0(\$2) 4(\$2) Initially, k is in reg 5; base address of v is in reg 4; Initially, return addr is in reg 31 return 2004 © Morgan Kaufman Publishers Spring 2013, Jan 25 . . . Spring ELEC 5200-001/6200-001 Lecture 3 15 What Happens? . . call swap . . . return address When the program reaches “call swap” statement: – Jump to swap routine Registers 4 and 5 contain the arguments (register convention) Register 31 contains the return address (register convention) – Swap two words in memory – Jump back to return address to continue rest of the Jump program program Spring 2013, Jan 25 . . . Spring ELEC 5200-001/6200-001 Lecture 3 16 Memory and Registers Memory byte addr. 0 4 8 12 . 4n . . . 4n+4k . Spring 2013, Jan 25 . . . Spring Word 0 Word 1 Word 2 Register 0 Register 1 Register 2 Register 3 v[0] (Word n) v[1] (Word n+1) Register 4 4n Register 5 k . . v[k] (Word n+k) v[k+1] (Word n+k+1) Register 31 ELEC 5200-001/6200-001 Lecture 3 Ret. addr. 17 Our First Example Now figure out the code: swap(int v, int k); { int temp; temp = v[k] v[k] = v[k+1]; v[k+1] = temp; } swap: sll \$2, add \$2, lw \$15, lw \$16, sw \$16, sw \$15, jr \$31 \$5, 2 \$4, \$2 0(\$2) 4(\$2) 0(\$2) 4(\$2) 2004 © Morgan Kaufman Publishers Spring 2013, Jan 25 . . . Spring ELEC 5200-001/6200-001 Lecture 3 18 So Far We’ve Learned MIPS — loading words but addressing bytes — arithmetic on registers only Instruction Meaning add \$s1, \$s2, \$s3 sub \$s1, \$s2, \$s3 lw \$s1, 100(\$s2) \$s1 = \$s2 + \$s3 \$s1 = \$s2 – \$s3 \$s1 = Memory[\$s2+100] sw \$s1, 100(\$s2) Memory[\$s2+100] = \$s1 2004 © Morgan Kaufman Publishers Spring 2013, Jan 25 . . . Spring ELEC 5200-001/6200-001 Lecture 3 19 Machine Language Instructions, like registers and words of data, are also 32 Instructions, bits long bits – Example: add \$t1, \$s1, \$s2 Example: – registers are numbered, \$t1=8, \$s1=17, \$s2=18 registers Instruction Format: 000000 10001 10010 01000 00000 100000 opcode rs rt rd shamt funct Can y...
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