At the time of the midterm exam, a student should be able to:

Timers

• Calculate the number of programmed timer events that occur in a given amount of time. For example, calculate the number of timer overflow events on Timer/Counter0 that would occur in 2 s if the timer were configured to divide a 16 MHz system clock by 1024 to generate the timer clock.
• Write C device driver subroutines to control timer events.
• Write C ISRs to respond to timer events.

Interrupts

• Compare and contrast polled and interrupt-driven systems.
• Indicate where the interrupt vector table is located in memory.
• Describe the purpose of the interrupt vector table.
• Explain the purpose for having specific control registers associated with particular interrupts.
• List the port pins that are shared as the external (global) interrupt pins.
• List example on-chip device interrupts.
• Explain the purpose of the I bit in the SREG register.
• Compare and contrast normal subroutines and ISRs.
• Write a simple interrupt service routine in C.
• Write a simple C program that initializes everything needed to enable a particular interrupt service routine.

C Programming Language

• Use C block (/* */) and inline (//) comment delimiters.
• Describe the basic syntax used to declare a C function.
• State the purpose of the void keyword.
• Described the use of the #include, #define, #ifndef, #ifdef, and #endif preprocessor directives.
• Use preprocessor directives to control header file conditional compilation.
• List and describe each of the C fundamental data types.
• Describe how the C99 standard enhances C data typing.
• Justify using C99 data types rather than C fundamental data types in embedded systems.
• Compare and contrast global variables and function variables.
• Describe how variables are made visible across files.
• State the type qualifier often needed with global variables modified by interrupt service subroutines.
• Use if-else, do-while, while, for, and switch flow control structures.
• Use the C inequality, equality, mathematic, bitwise, and assignment operators.
• Compare and contrast passing values and pointers as function parameters.
• Justify the use of function prototypes.
• Describe how C arrays are declared, initialized, and indexed.
• Describe the use of pointers to directly access memory and the use of pointers in call-by-reference function parameters.
• Use pointer declaration and pointer dereferencing in C functions.
• Use pointer arithmetic with pre/post increment and pre/post decrement operators to move through data in memory.
• Compare and contrast initialized pointers, null pointers, and dangling pointers.
• State how null pointers can be used in conditional statements to prevent memory access violations.
• State the name of the header file that declares I/O control registers by name.
• State the name of the header file that declares the C99 types.
• State the name of the header file that assigns names to the jump vectors and declares the sei and cli functions.

Mixing C and Assembly

• Understand the GNU compiler's use of temporary and saved registers. In particular,
  • Explain the differences in how the GNU compiler handles temporary and saved registers.
  • Describe the steps that must be taken when using a temporary register in an assembly function that was called from C.
  • Describe the steps that must be taken when using a temporary register in assembly that calls a C function.
  • Describe the steps that must be taken when using a saved register in an assembly function that was called from C.
  • Describe the steps that must be taken when using a saved register in assembly that calls a C function.
• State which register GCC assumes contains zero at all times and describe how to accomodate this when writing assembly code that is mixed with C.
• Demonstrate proper use of the GCC assembler syntax (be aware of the syntax differences between GCC and the AVR assembler).
• Describe how parameters are passed between C and assembly functions.
• Describe the purpose of an object file (.o).
• Explain the purpose of the linker used when compiling programs with GCC.
• Translate functions written in assembly into C functions.
• Indicate when the extern and .global keywords are required and explain what they do.
• Interpret disassembled C code.
• Explain how local variables (inside C functions) are stored in memory.