General Purpose Processors

Question 1

Instruction cycle for a GPP?

Answer 1

1. Fetch from PC location
2. Decode
3. Fetch Operands to Data Path from Memory
4. Execute
5. Store to Memory

Question 2

What does the PC size specify?

Answer 2

It specifies the program adress space, ie. if the PC is 10bits large -> the memory can have 2^10 words (bytes)

Question 3

What limits the clock period of a processors?

Answer 3

The operations in the instruction cycle, typically the memory access takes the longest time

Question 4

Why is a branching a problem for pipelining? What are possible solutions?

Answer 4

(branching = if/loops) –> it is unknown what to load next in a branch

• add delays (insert empty bubble instead of fetching next)
• default decision (if there is a branch, is it taken or not)

Question 5

What is the difference between von Neumann and Harvard architectures?

Answer 5

Von-Neumann: one memory for programm and data together (one bus -> is bottleneck)
Harvard: one memory for programm and one memory for data (two busses) –> more performant

Question 6

Advantages of Harvard architechture?

Answer 6

• parallel fetching of data and instructions
• optimized storage technology for each purpose
• memory protection (program unable to change during runtime)

! this architecture is also used by the AVR

Question 7

What is -gcc actually taking care of? (5 steps)

Answer 7

1. Preprocessor (including headers, macros, conditional compilation)
2. Compiler (translate human readable code into assembly for a particular processor)
3. Assembler (translates assembly into opcodes, produces object file) - “start-up-code” required (AVR)
4. Linker (organizes obejct files, libraries and other data and produces a relocatable file –> first addressing)
5. takes relocatable file and information about system’s memory and produces an executable file

Question 8

Name two options to get your program onto the embedded device.

Answer 8

• ISP (in-system programming) –> programmed while installed in a complete system (fast)
• bootloader –> dedicated memory space where startup information is located and flashed on via serial connection (slower)

Question 9

Advantages of von Neumann architecture?

Answer 9

• program can be treated as data –> reading from disk storage and executing it
• better memory utilization (program memory = data memory)