Bitwise Operators

Pointers

Functions

Structs

Interrupts

(in C)

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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: http://www.cs.cf.ac.uk/Dave/C/node13.html

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Examples of c operations at the byte level

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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)

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Using shift operators (remember these are logical):

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Redoing the previous problem with shifts:

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Getting data from the port:

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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

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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

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Pointers: example data

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Example instruction:

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Example 2 of Instruction execution

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Example: what is output?

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Pointer arithmetic—not for beginners!

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Pointer arithmetic: additional examples

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Constant pointers:

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Using constants and constant pointers:

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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

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C functions:

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Example:

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Function call: note order of parameters on stack

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Using stack to return result:

Function body in memory:

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Pass by value (default in c):

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Pass by reference:

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

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Function documentation: template for header

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We can also define pointers to functions:

Dereferencing methods:

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Example:

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Example 2:

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Pointing to add:

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

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User-defined data structure: struct

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User-defined data structure: struct

Example:

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Can also define a type and use it repeatedly:

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Syntax for using struct:

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Example: define a rectangle

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One struct using another:

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C code for this example:

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Definign the rectangle type:

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Using point and rectangle definitions:

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Rectangle functions:

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Example program:

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Example: passing a struct to a function:

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

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How an interrupt occurs:

Interrupt may be disabled under certain conditions

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Enable / disable control mechanisms:

Global

Maskingmethod 1: use prioritiesmethod 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