Bitwise Operators Pointers Functions Structs Interrupts (in C)

table_07_00 Bitwise operators: useful for dealing with signals of different widths; NOTE: these are LOGICAL operators and variables are declared UNSIGNED— why? (example: homework 1, problem 1) Additional useful reference:

fig_07_00 Examples of c operations at the byte level

fig_07_01 Example of c program—”portShadow” mirrors what is on port; Note use of parentheses to guarantee order of bitlevel operations (even if we are using default order)

fig_07_02 Using shift operators (remember these are logical):

fig_07_03 Redoing the previous problem with shifts:

fig_07_04 Getting data from the port:

fig_07_05 Using bitlevel operations for arithmetic; Are there any problems with this approach? C: on signed data, left shift undefined if overflow occurs, right shift is implementation-dependent; Java: all integers are signed

fig_07_06 Can use shifts for slightly more complex multiplies and divides; More complex operations (e.g., with 3 1’s in multiplier or divider) are probably not efficient

fig_07_07 Pointers: example data

fig_07_09 Example instruction:

fig_07_10 Example 2 of Instruction execution

fig_07_11 Example: what is output?

fig_07_12a Pointer arithmetic—not for beginners!

fig_07_12b Pointer arithmetic: additional examples

fig_07_13 Constant pointers:

fig_07_14 Using constants and constant pointers:

fig_07_14 Note: pointers can be “generic” or NULL: Generic: Type void: pointer can point to a variable of any type example: 7.3, p. 265 NULL: Pointer needs to be assigned a valid address before dereferencing, otherwise hard-to-find bugs can occur Address 0 is not acceptable Solution: use null pointer address, (void*) 0

fig_07_15 C functions:

fig_07_16 Example:

fig_07_17 Function call: note order of parameters on stack

fig_07_18 Using stack to return result: Function body in memory:

fig_07_20 Pass by value (default in c):

fig_07_21 Pass by reference:

fig_07_22 Information hiding: static qualifier prevents visibility outside this file (even to linker):

fig_07_23 Function documentation: template for header

fig_07_24 We can also define pointers to functions: Dereferencing methods:

fig_07_26 Example:

fig_07_27 Example 2:

fig_07_28 Pointing to add:

fig_07_29 Pointing to subtract: pointer does not know functionality, only address

fig_07_31 User-defined data structure: struct

fig_07_30 User-defined data structure: struct Example:

fig_07_34 Can also define a type and use it repeatedly:

fig_07_35 Syntax for using struct:

fig_07_36 Example: define a rectangle

fig_07_37 One struct using another:

fig_07_38 C code for this example:

fig_07_39 Definign the rectangle type:

fig_07_40 Using point and rectangle definitions:

fig_07_41 Rectangle functions:

fig_07_42 Example program:

fig_07_43 Example: passing a struct to a function:

fig_07_44 Interrupt service routines: ISR—needs to be SHORT and SIMPLE

fig_07_45 How an interrupt occurs: Interrupt may be disabled under certain conditions

fig_07_46 Enable / disable control mechanisms: Global Masking method 1: use priorities method 2: use mask register (bitwise masks) Note: interrupts are transient, if we choose to ignore one we may not be able to service it later