课程名称︰计算机结构 课程性质︰必修 课程教师︰洪士灏 开课学院：电资学院 开课系所︰资工系 考试日期（年月日）︰2016/11/17 考试时限（分钟）：180分钟左右 试题 : 1. (30pts) A lot of people are taling about Internet of Things(IoT). According to Wikipedia: IoT is the internetworking of physical devices, vehicles(also referred to as "connected devices" and "smart devices"), buildings and other items -- embedded with electronics, software, sensors, actuators, and network connectivety that enable these objects to collect and exchange data. The IoT allows objects to be sensed and/or controlled remotely across existing network infrastructure, creating opportunities for more direct integration of the physical world into computer-based systems, and resulting in improved efficiency, accracy and economic benefit. Experts estimate that the IoT will consist of almost 50 billion objects by 2020. Typically, IoT is expected to offer advanced connectivity of devices, systems, and services that goes beyond machine-to-machine (M2M) communications and covers a variety of protocols, domains, and applications.The interconnection of these embedded devices (including smart objects), is expected to usher in automation in nearly all fields, while also enabling advanced applications like a smart grid, and expanding to the areas such as smart cities. "Things," in the IoT sense, can refer to a wide variety of devices such as heart monitoring implants, biochip transponders on farm animals, electric clams in coastal waters, automobiles with built-in sensors, DNA analysis devices for environmental/food/pathogen monitoring or field operation devices that assist firefighters in search and rescue operations. Legal scholars suggest to look at "Things" as an "inextricable mixture of hardware, software, data and service".These devices collect useful data with the help of various existing technologies and then autonomously flow the data between other devices. Current market examples include home automation (also known as smart home devices) such as the control and automation of lighting, heating (like smart thermostat), ventilation, air conditioning (HVAC) systems, and appliances such as washer/dryers, robotic vacuums, air purifiers , ovens or refrigerators/freezers that use Wi-Fi for remote monitoring. As well as the expansion of Internet-connected automation into a plethora of new application areas, IoT is also expected to generate large amounts of data from diverse locations, with the consequent necessity for quick aggregation of the data, and an increase in the need to index, store, and process such data more effectively. IoT is one of the platforms of today's Smart City, and Smart Energy Management Systems. The concept of the Internet of Things was invented by and term coined by Peter T. Lewis in September 1985 in a speech he delivered at a U.S. Federal Communications Commission (FCC) supported session at the Congressional Black Caucus 15th Legislative Weekend Conference. Please answer the following questions as complete as possible. (a)(10pts)Since the concept of IoT was "invented" in 1985, why do people start to talk about it until recently?(There are several reasons). (b)(10pts)What kind(s) of computers are needed for this IoT Era? For each kind , please list example applications, describe its typical system configuration and the design issues. (c)(10pts)Similar things can be said about the rise of Artificial Intellifence (AI) in recent years. Actually, AI was very popular in '80s, but it suddenly stopped to talk about it(at least from the industry's point of view) Why? How does this relate to computer architecture? 2. (20pts)Please answer the following questions after reading the MIPS assembly code in the next page. Note that you do NOT need to understand the entire program to analyze the performance, as compilers and processors do not understand the entire program either. The instruction bltz is "branch on less than zero", which branches to the label if the register is less than zero. You can write your ansewers directly on Page 3. (a)(10pts)A basic block is a sequence of instructions without branches, except possibly at the end, and without branch targets or branch labels, except possibly at the beginning. One of the first early phases of compilation is breaking the program into basic blocks. Please identify all the basic block(s) in this assembly code. (b)(10pts)A data dependency in computer science is a situation in which a program statement(instruction) refers to the data of a preceding statement. Please identify all the data dependencies in this assembly code. ASSEMBLY CODE 1 start: 2 lw $t0, 0($gp) #fetch i 3 bltz $t0, def #i<0 ->default 4 slti $t1, $t0, 3 #i<3? 5 beq $t1, $zero, def #no, -> default 6 sll $t0, $t0, 2 #turn i into a byte offset 7 add $t2, $t0, $gp 8 lw $t2, 1064($t2) #fetch the branch table entry 9 jr $t2 #go... 10 is0: sw $zero, 28($gp) #A[0] = 0 11 j case_done 12 is1: 13 is2: addi $t0, $zero, 1 # = 1 14 sw $t0, 32($gp) #A[1] = 1 15 j case_done 16 def: addi $t0, $zero, -1 # = -1 17 sw $t0, 28(gp) #A[0] = -1 18 j case_done 19 case_done: 20 lw $t0, 0($gp) #fetch i 21 lw $t1, 4($gp) #fetch N 22 alt $t1, $t0, $t1 #set $t1 to 1 if $t0 < $t1, to 0 otherwise 23 beq $t1, $zero, skip #branch if result of slt is 0(i.e., !(i<N)) 24 sll $t0, $t0, 2 #i as a byte offset 25 add $t0, $t0, $gp #&A[i] - 28 26 sw $zero, 28($t0) #A[i] = 0 27 skip: 28 add $t0, $gp, $zero #&A[0] - 28 29 lw $t1, 4($gp) #fetch N 30 sll $t1, $t1, 2 #N as byte offset 31 add $t1, $t1, $gp #&A[N] - 28 32 ori $t2, $zero, 256 #MAX_SIZE 33 top: 34 sltu $t3, $t0, $t1 #have we reached the final address? 35 beq $t3, $zero, loop_end #yes, we're done 36 sw $t2, 28($t0) #A[i] = 0 37 addi $t0, $t0, 4 #update $t0 to point to next element 38 j top #go to top of loop 39 loop_end: -ASSEMBLY END- 3. (40pts)Let us analyze the performance of the assembly code on Page 3 for the 5-stage pipelined MIPS datapath shown below. Note that the branch instruction are handle in the EX stage, and there is no data forwarding unit. (a)(10pts)Data hazards can stall the pipeline and cause pieline bubbles. Data hazards mainly come from data dependencies, but not all data dependencies can cause data hazards. Please identify all the pipeline bubbles cause by data hazards in the assembly code. (b)(10pts)Control hazards can stall the pipeline and cause pipeline bubbles. Please identify all the pipeline bubbles cause by control hazards in the assembly code. (c)(10pts)Branch prediction can reduce the penalty caused by contrl hazards only if the prediction is correct. Please discuss the likelihood of correct prediction for the branches in the assembly code. Which branches can be predicted with high probability? Why? (d)(10pts)Loop unrolling is a common technique to eliminate data hazards and speed up the execution. If you have not noticed, Lines 33~39 constitute a loop. Please unroll the loop 4 times(write down the unrolled code on the answer sheet) and estimate the resulted performance. 4. (10pts)Assume we have convented the processor in Problem 3 into a static dual-issue processor, which can execute 2 instructions per cycle, as shown in the following figure. Instruction type Pipe stages ALU or branch instruction IF ID EX MEM WB Load or store instruction IF ID EX MEM WB ALU or branch instruction IF ID EX MEM WB Load or store instruction IF ID EX MEM WB ALU or branch instruction IF ID EX MEM WB Load or store instruction IF ID EX MEM WB ALU or branch instruction IF ID EX MEM WB Load or store instruction IF ID EX MEM WB (a)(5pts)Calculate the number of cycles needed to execute the assembly codes for the loop constituted by Lines 33~39 on Page 3. (b)(5pts)Calculate the number of cycles needed to execute the assembly codes for the loop after you unroll it 4 times as in your answer to Question 3(d). --

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