$1.$ The ARM processor is interfaced with two sensors utilized for object detection, and a control unit that enables transfer of data in$/$out of memory with minimal interference from the processor. When the processor is executing the main program, a timer is triggered to count from $100$ to $0.$ In this case, when the counter reaches $50,$ the first sensor is triggered to detect an object, and when an object is detected the processor utilizes information acquired from the sensor to calculate the distance, and store the results in memory, then the counter continues decrementing. However, when the counter reaches $0$ the second sensor is triggered to detect an object, and when an object is detected the control unit transfers data from the sensor to memory. Once data from the second sensor is stored in memory a new value is loaded into the counter to enable the counter to re$-$start the process again $[34$ Marks$]$

a$)$ Name and explain the operating mode of the timer $[3$ Marks$]$

b$)$Name and explain two registers used to disable and enable the timer in order to move the c$)$processor to SVC mode then back to user mode when the timer is disabled. Also explain how the bits will be configured for the two registers.

d$)$Name and explain the register used to hold the count value when the counter reaches $50$

e$)$Name and explain two registers that will hold the count value $100$

f$)$Name and explain three registers used by the control unit to transfer data to memory