EE345M Final Exam A Fall 2006 Page 1 of 9 Jonathan W Valvano First Name Last Name December 18 2006 9am 12n This is an open book open notes exam You must put answers on these papers please don t turn in any extra sheets 20 Question 1 The goal is to measure the speed of a rotating shaft with a resolution of at least 0 1 rpm using input capture on PT7 A white black disk is placed on the shaft and an optical sensor is located near the disk When the motor is spinning an oscillating waveform is measured so that there is a minimum voltage of about 2V when the white part is visible and a maximum voltage of about 4V when the black part is visible There are 32 lines Part a Interface this sensor to the 9S12C32 Specify chip numbers and resistor values as needed The 74HC14 can not be used because the voltage range is too high instead consider using a rail to rail op amp to create a CMOS logic compatible signal 5 200 5 5k 4V 2V EE345M Final Exam A Fall 2006 Page 2 of 9 Part b Write the software required to measure shaft speed You may assume the maximum speed is 120 RPM or 2 rps Include an initializing ritual and ISR s which measure the shaft speed quickly and accurately Maintain a global variable with the most recent speed measurement EE345M Final Exam A Fall 2006 Page 3 of 9 20 Question 2 The current to a DC motor depends on both the applied voltage and its mechanical load The following data was collected from the DC motors we used in Lab 30 Condition Voltage Current Speed No load 9V 35 mA 150 RPM Normal load 9V 100 mA 90 RPM Stalled 9V over 200 mA 0 RPM When the robot strikes a wall or another robot either the wheels will spin or the motor will stall Design a hardware software system that detects a stalled motor by measuring the delivered current to the motor in a minimally intrusive manner The overall goal is to set a global variable called bStall to 1 if the current exceeds 200 mA Part a The following shows a typical DC motor interface Modify it so that there is an analog signal that is proportional to the motor current can be measured Connect that signal to PAD0 You only need to make it work spinning forward 4Y 8 4V and 3Y 0V Be careful to limit the ADC input voltage to levels between 0 to 5V You can use a 1 watt resistor EE345M Final Exam A Fall 2006 Page 4 of 9 Part b Write the software required to detect a stalled motor Use a periodic output compare ISR that measures the current every 10 ms and sets the bStall 1 if the current is greater than 200 mA You may use ADC Init and ADC In without showing the code but all other software is required EE345M Final Exam A Fall 2006 Page 5 of 9 5 Question 3 Consider a situation where two 9S12C32 systems are connected with a CAN network Computer 1 generates 8 bit data packets that must be sent to computer 2 and computer 2 generates 8 bit data packets that must be sent to computer 1 The packets are generated at random times and the goal is to minimize the latency between when a data packet is generated on one computer to when it is received on the other Describe the CAN protocol you would use 11 bit versus 29 bit ID Number of bytes of data Bandwidth Clearly describe what is in the ID and how the data is formatted 5 Question 4 The following multithreaded system has a critical section Modify these programs to remove the error You may assume the RTI interrupts are enabled and are running The unsigned long data type is a 32 bit integer unsigned long Time void main void void interrupt 7 handler while 1 PTT 0x01 if Time 1000000 CRGFLG 0x80 SCI OutString done Time PTT 0x01 ack EE345M Final Exam A Fall 2006 Page 6 of 9 20 Question 5 This problem investigates the design of an adaptive priority scheduler with exponential time slices This is also called an exponential Queue or multi level feedback queue The CTSS system MIT early 1960 s was the first to use exponential queues One of the difficulties in a priority scheduler is the assignment of priority Typically one wishes to assign a high priority to threads doing I O which block a lot so that the response to I O is short and assign a low priority to threads not doing I O which do not block a lot However in a complex system a particular thread may sometimes exhibit I O bound behavior but later exhibit CPU bound behavior An adaptive scheduler will adjust the priority according to the current activity of the thread Priority 1 threads will run with a time slice of 4000 1ms priority 2 threads will run with a time slice of 8000 2ms and priority 3 threads will run with a time slice of 16000 4ms Consider this blocking round robin scheduler with two new entries shown in bold added to the TCB struct TCB struct TCB Next Link to Next TCB char StackPt Stack Pointer Sema4Type BlockPt 0 if not blocked pointer if blocked short Priority 1 highest 2 or 3 lowest unsigned short TimeSlice 4000 8000 or 16000 char Stack 100 stack size determined at runtime typedef struct TCB TCBType typedef TCBType TCBPtr Part a Rewrite the OS Wait function so that if a priority 2 or 3 thread blocks its priority will be raised decrement by 1 and its time slice will be halved No changes to OS Signal will be needed void OS Wait Sema4Type semaPt asm sei Test and set is atomic semaPt Value if semaPt Value 0 RunPt BlockPt semaPt block this thread TC3 TCNT 15 stop running this thread asm cli EE345M Final Exam A Fall 2006 Page 7 of 9 Part b Rewrite the threadSwitch ISR so that if a priority 1 or 2 thread runs to the end of its time slice without blocking its priority will be lowered increment by 1 and its time slice will be doubled In addition implement priority scheduling with variable time slices this is a round robin scheduler with fixed timeslices interrupt 11 void threadSwitch void asm ldx RunPt asm sts 2 x RunPt RunPt Next while RunPt BlockPt RunPt RunPt Next don t run blocked threads TC3 TCNT 4000 Thread runs for a unit of time TFLG1 0x08 acknowledge by clearing TC3F asm ldx RunPt asm lds 2 x EE345M Final Exam A Fall 2006 Page 8 of 9 10 Question 6 The Lab 30 DC motor will be controlled using a 9S12C32 system The speed is measured using 16 bit input capture and has a measurement resolution of 0 1 rpm The input capture device driver repeatedly updates a global variable called Speed This 16 bit unsigned variable has units of 0 1 rpm and a …