Winter 2013 MIDTERM TEST #2 Wednesday, March 20 7:00pm to 8:15pm. Please do not write your U of C ID number on this cover page.

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1 page of 7 University of Calgary Departent of Electrical and Copter Engineering ENCM 369: Copter Organization Lectre Instrctors: Steve Noran and Nor Bartley Winter 23 MIDTERM TEST #2 Wednesday, March 2 7:p to 8:5p Please do not write yor U of C ID nber on this cover page. Nae (printed): Signatre: Lectre section ( is MWF :a with S. Noran, 2 is MWF :a with N. Bartley): General Instrctions Marks will be recorded on the last page of this qestion paper. When yo are told to start the test, the first thing yo shold do is to pt yor nae, signatre, U of C ID nber, and lectre section in the appropriate spaces at the botto of the last page. Yo ay not se electronic calclators or copters dring the test. The test is closed-book. Yo ay not refer to books or notes dring the test, with one eception: yo ay refer to the Reference Material booklet that accopanies this test paper. Yo are not reqired to add coents to assebly langage code yo write, bt yo are strongly encoraged to do so, becase writing good coents will iprove the probability that yor code is correct and will help yo to check yor code after it is finished. Soe probles are relatively easy and soe are relatively difficlt. Go after the easy arks first. To redce distraction to other stdents, yo are not allowed to leave dring the last ten intes of the test. all answers on the qestion paper and hand in the qestion paper when yo are done. Please print or write yor answers legibly. What cannot be read cannot be arked. If yo write anything yo do not want arked, pt a large X throgh it and write rogh work beside it. Yo ay se the backs of pages for rogh work.

2 ENCM 369 Winter 23: Midter #2 page 2 of 7 PROBLEM ( arks). In the C code to the right, foo replaces each space character in a string with a * character, and conts how any sch replaceents it does. Translate foo into MARS assebly langage. Follow the sal calling conventions fro lectres and labs, and se only instrctions fro the Midter Instrction Sbset described in the Reference Material booklet. Reinder: Character constants sch as and * ay be sed as operands in soe MARS instrctions. int foo(char *s) { int k, cont; cont = ; for (k = ; s[k]!= \ ; k++) if (s[k] == ) { s[k] = * ; cont++; } retrn cont; }

3 ENCM 369 Winter 23: Midter #2 page 3 of 7 PROBLEM 2 (total of arks). Part a (5 arks). Sppose in a MIPS processor $t contains a_3 and $t contains 2fff_ffff. The processor then eectes sb $t2, $t, $t. Epress the 32-bit sbtraction reslt in headecial forat. Show yor work. Was there overflow in the sbtraction? Give a reason for yor answer. Was there wraparond in the sbtraction? Give a reason for yor answer. Does the reslt get copied into $t2? Why or why not?. Part b (3 arks). Sppose in a MIPS processor $s7 contains 7fff_f, and then addi $s7, $s7, is eected. What will be the vale of $s7 after the instrction is finished? Show yor work. Was there overflow in the sbtraction? Give a reason for yor answer. Part c (2 arks). Sppose $a contains a_3. What will be in $t9 after this instrction is eected: srl $t9, $a, 3? Epress yor answer in headecial forat. Part d (2 arks). Sppose $a contains abcd_5a. What will be in $t5 after this instrction is eected: andi $t5, $a, f7? Epress yor answer in headecial forat. Part e (2 arks). If the bit pattern ffff_ffff_ffff_ffff_ffff_ffff_ffff_ffbd is sed for a 28-bit two s copleent integer, what nber does it represent? Show yor work, and epress yor answer in base ten.

4 ENCM 369 Winter 23: Midter #2 page of 7 PROBLEM 3 (total of arks) This proble concerns a single-cycle copter design to spport a sbset of MIPS instrctions inclding byte loads and stores... Which bits? Control Jpiter W/B Me Me Mars ALU operation Vens Reg Mercry PC Instrction Instrction eory bits 25-2 bits 2-6 bits 5- reg reg 2 reg data Reg- data data 2 GPRs Zero ALU Reslt Me- Me- W/B data data Data eory 8-to-32- bit signetend bits 7- bits 3-2 bits 5-6-to-32- bit signetend 32 shift left 2 clock The copter has a Data eory with an etra -bit inpt called W/B (word/notbyte), which is not present in the Data eory in designs seen in yor corse tetbook. Data eory behavior is given in this table: Me- Me- W/B Data eory behavior X idle byte at pdated with bits 7 of data word at pdated with bits 3 of data bits 7 of data = byte fro bits 3 8 of data are all zero data = word fro X npredictable this case shold be avoided Part a (2 arks). The copter has a Control nit that erges the roles of the ain control nit and the ALU control nit in designs stdied in the tetbook and lectres. For this to work correctly, the Control nit st get 2 bits of inpt fro the instrction. Which 2 bits are needed? Give a brief eplanation for yor answer. Part b (2 arks). How any inpt wires are there for the three-inpt ltipleer nearest to the far right side of the circit diagra? Inclde both data inpts and select inpts. Show how yo obtained yor answer. The proble contines on the net page...

5 ENCM 369 Winter 23: Midter #2 page 5 of 7 PROBLEM 3... contined fro the previos page... Part c ( arks). Coplete the table below, sing s and s, and X s for don t-cares. Soe of the answers for BEQ have been written in as eaples. Note that instrction forats and the ALU specification are given to yo in the Reference Material booklet. Instrction LW LB LBU SW SB Mercry Reg Vens ALU operation Mars Me Me W/B Jpiter BEQ X X XX ADD SUB AND OR SLT sae as ADD sae as ADD For convenience, the circit diagra and table fro the previos page are repeated below. Which bits? Control Jpiter W/B Me Me Mars ALU operation Vens Reg Mercry PC Instrction Instrction eory bits 25-2 bits 2-6 bits 5- reg reg 2 reg data Reg- data data 2 GPRs Zero ALU Reslt Me- Me- W/B data data Data eory 8-to-32- bit signetend bits 7- bits 3-2 bits 5-6-to-32- bit signetend 32 shift left 2 clock Me- Me- W/B Data eory behavior X idle byte at pdated with bits 7 of data word at pdated with bits 3 of data bits 7 of data = byte fro bits 3 8 of data are all zero data = word fro X npredictable this case shold be avoided

6 ENCM 369 Winter 23: Midter #2 page 6 of 7 PROBLEM (total of 6 arks). All parts concern eection of the following instrction seqence by the copter of Figre.5 of the corse tetbook; a copy of this figre is on page 5 of the Reference Material booklet. The clock period is. ns. Updates to the PC, pipeline register, and Data Meory occr at t =. ns, t =. ns, t = 2. ns, and so on. Updates to the register file occr at t =.5 ns, t =.5 ns, t = 2.5 ns, and so on. The following is part of the progra rnning in the copter: address instrction disassebly _5 _ NOP _5 _ NOP _58 _ NOP _5c 8d28_ LW $8, ($9) _6 85_7822 SUB $5, $, $5 _6 8_52 ADD $, $, $8 _68 68_5825 OR $, $, $8 The IF step for the lw instrction starts at t =. ns, and at that tie contents of soe GPRs and data eory locations are as follows: REGISTERS DATA MEMORY $ = ffff_ffff address contents $5 = a _ff $8 = _2 _a _ee $9 = _a _a8 _dd $ = 6 ac _cc $ = 7 b _bb Yo ay wish to se the clock signal below and the blank space beneath it for rogh work. For each of parts b f, give a brief eplanation of yor answer, sing the answer to part a as a odel. Use base siteen for 32-bit nbers and base two for 5-bit nbers. Part a ( arks). What is written into the IF/ID.Instrction field at t =. ns? 8d28_ achine code for the LW instrction. Part b ( ark). What is written into the PC at t =. ns? Part c ( ark). What is written into the ID/EX.A field at t = 2. ns? Part d ( ark). What is written into the EX/MEM.Reslt field at t = 3. ns? Part e ( ark). What is written into the EX/MEM.RegisterRd field at t =. ns? Part f (2 arks). What vales get written into GPRs $ and $ by the ADD and OR instrctions?

7 ENCM 369 Winter 23: Midter #2 page 7 of 7 PROBLEM 5 (total of 6 arks) iscellaneos topics. Part a (3 arks). Consider a MIPS assebler that prodces object files as its otpt. The asseber is part of a toolchain that can be sed to create eectable files starting with C sorce code. For one of the beq and j instrctions, the assebler cannot generate correct achine code. Which instrction is that, and why? Briefly eplain how the correct achine code for that instrction will appear in the eectable file. Part b (2 arks). This diagra belows shows Stage G, the seventh stage in a ten-stage pipelined processor design. Pipeline registers Reg F/G and Reg G/H are ade of positive-edge triggered D flip-flops with t PCQ = 5 ps and t setp = 25 ps. Reg F/G Crnch Mnge Zork Reg G/H Twiddle clock Sppose propagation delays (t PD ) for cobinational nits are as follows: 8 ps for Crnch, 2 ps for Mnge, 3 ps for Twiddle, and 2 ps for Zork. What is the ini clock period to allow safe operation of Stage G? Show yor work. Part c ( ark). la $a, 2($sp) is a psedoinstrction in MIPS and MARS assebly langage. What is the assebly langage for a real instrction that has the sae effect? MARKS: The space below will be sed to record yor arks for each qestion and yor overall test ark. Please pt yor nae, signatre, and U of C ID nber in the appropriate boes. Nae (printed): Signatre: Proble Mark / 2 / U of Calgary ID nber: 3 / / 6 5 / 6 Lectre Section ( is :a, 2 is :a): TOTAL / 5