s11_hw2_solution - 4.4 Extend the SRC instruction set by...

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Unformatted text preview: 4.4 Extend the SRC instruction set by adding the xor command, (op = 19), which is similar to the and command, but performs the XOR operation instead of AND. a.Develop the abstract RTN for the xor command. b.Write the concrete RTN and control signals for the xor instruction for the 1-bus SRC microarchitecture. (Unfortunately. the SRC ALU does not have the XOR operation as one ofits primitives, but only the operations ADD, SUB, AND, OR, SHR, SHL, NEG‘ NOT. C : B. and INC4.) Solution: 21. xort := op = 19 ) —> R[ra] <— R[rb] XOR R[rc]: b.Using the definition a xor b = aA-b v aaAb cow/mm — ‘ - p—I 4.7 The SRC instruction set includes the neg instruction, which computes the arithmetic 2’s complement negation of a register operand. Assume that the NEG operation is not in the set of operations the ALU can perform. (See page 152.) Develop the concrete RTN and the control sequence to implement the neg instruction for the l-bus design. (§4.4) Solution: The NEG instruction can be implemented using the SUB instruction by subtract— ing the operand from zero to get its negative. Concrete RTN and control sequences for instruction NEG for l-bus design follow: Step RTN Control sequence T MA <— PC: C <—— PC + 4; PCOm, MAin, INC4, Cm MD <— M[MA]: PC <— c; com, PCm, Read. Wait T T . IR <— MD; MDout, 1Rin . A <— ol; Ain 0 2 3 C <— A — R.[rc]; Grc, Rout', SUB, Cin Rim] 6 TNote: Assume a passive pull-down on the bus, so that it is 0 if no 3—state gates are active. Com, Gra, Rout, End Bus 32 32 4.8 Using Tables 4.6 to 4.1 1, develop as much as you can ofthe control signals MDom, Cm, and LD. Show both the Boolean equations and the gate—level designs. (§4.5) Solution: MDDUI = T2 + T7-ld + Cm = TO + T4-{add + addi + 1d) + TG-Shr + Ld = T4.shr+ T2 T7 Id 4.13 The 2-bus SRC design shown in Figure 4.16 allows savings in the number of control steps to perform an add instruction, but at the expense of additional control hardware. The text describes the need Io provide additional gate and strobe hardware so that data can be gated from and strobed to the general registers on the Same cycle. Redesign the hardware shown in Figure 4.4 to accommodate this change. Solution: flaw. 551.3 31 EN '22 2'1 1715 1211 heath: tricth- 4.16 Repeat Exercise 4.? for the 2- and 3-bus microarchiteetures. (§4.6) Solution: Concrete RTN and control sequences for NEG in a 2-bus design: j Control sequence | Pcout: MAin. C33 | Pcom,1NC4, Pcm, Read, Wait t MDout! lRins (3:8 Ain | Grc, Rom, SUB, Sra,Rl-n,13nd RTN Control sequence MA 4— PC: MD t— MIMA]: PC MAin, INC4, PCin, Read, Wait PC *— PC + 4; IR *— MD; Mom“, 111m, C=B Rm] 5 0* — R[rc]; Grc, Rm", SUB. Sra, Rm, End out ‘ TNote: Assume a passive pull-down on the bus, so that it is 0 if no 3-state gates are active. Bus 32 32 ...
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