1. Sequential Statements (Lecture 2)
Osman Hasan
COEN 313

2. Outline
If statement
Case Statement
For loop Statement

3. If Statement Sequential Conditional Statement in VHDL Syntax
if boolean_expr_1 then
sequential_statements;
elsif boolean_expr_2 then
elsif boolean_expr_3 then
. . .
else
end if;
Safety critical system failure could cause human life.
Commercial critical systems: great financial loss if the product is recalled or is found to contain bugs
Examples of undetected errors
– Ariane 5 rocket explosion, 1996 (exception occurred
when converting 64-bit floating number to a 16-bit
integer)
– Pentium bug (multiplier table not fully verified)
– many more ….
Somehow make debugging happen earlier where it is cheaper 3 3

4. If Statement – Conceptual implementation
Safety critical system failure could cause human life.
Commercial critical systems: great financial loss if the product is recalled or is found to contain bugs
Examples of undetected errors
– Ariane 5 rocket explosion, 1996 (exception occurred
when converting 64-bit floating number to a 16-bit
integer)
– Pentium bug (multiplier table not fully verified)
– many more ….
Somehow make debugging happen earlier where it is cheaper 4 4

5. If Statement – Comparison to conditional signal assignment
If statement is more flexible
Multiple Statements may share the same Boolean Condition
Nesting
Safety critical system failure could cause human life.
Commercial critical systems: great financial loss if the product is recalled or is found to contain bugs
Examples of undetected errors
– Ariane 5 rocket explosion, 1996 (exception occurred
when converting 64-bit floating number to a 16-bit
integer)
– Pentium bug (multiplier table not fully verified)
– many more ….
Somehow make debugging happen earlier where it is cheaper 5 5

6. If Statement – “sharing” Boolean condition Example
Safety critical system failure could cause human life.
Commercial critical systems: great financial loss if the product is recalled or is found to contain bugs
Examples of undetected errors
– Ariane 5 rocket explosion, 1996 (exception occurred
when converting 64-bit floating number to a 16-bit
integer)
– Pentium bug (multiplier table not fully verified)
– many more ….
Somehow make debugging happen earlier where it is cheaper 6 6

7. Quiz 1: Maximum of 3 numbersc
VHDL
(Using If statemets)
max
Safety critical system failure could cause human life.
Commercial critical systems: great financial loss if the product is recalled or is found to contain bugs
Examples of undetected errors
– Ariane 5 rocket explosion, 1996 (exception occurred
when converting 64-bit floating number to a 16-bit
integer)
– Pentium bug (multiplier table not fully verified)
– many more ….
Somehow make debugging happen earlier where it is cheaper 7 7

8. Common Mistakes!
Incomplete Branch
Equality Checker
‘0’

9. Common Mistakes! Incomplete Signal Assignment
Equality/Inequality Checker

10. Outline
If statement
Case Statement
For loop Statement 10 10

11. Case Statement Sequential Conditional Statement in VHDL Syntax
case case_expression is
when choice_1 =>
sequential statements;
when choice_2 =>
. . .
when choice_n =>
end case;
Safety critical system failure could cause human life.
Commercial critical systems: great financial loss if the product is recalled or is found to contain bugs
Examples of undetected errors
– Ariane 5 rocket explosion, 1996 (exception occurred
when converting 64-bit floating number to a 16-bit
integer)
– Pentium bug (multiplier table not fully verified)
– many more ….
Somehow make debugging happen earlier where it is cheaper 11 11

12. Case Statement – Conceptual implementation
Safety critical system failure could cause human life.
Commercial critical systems: great financial loss if the product is recalled or is found to contain bugs
Examples of undetected errors
– Ariane 5 rocket explosion, 1996 (exception occurred
when converting 64-bit floating number to a 16-bit
integer)
– Pentium bug (multiplier table not fully verified)
– many more ….
Somehow make debugging happen earlier where it is cheaper 12 12

13. Example: 4x1 Mux
Safety critical system failure could cause human life.
Commercial critical systems: great financial loss if the product is recalled or is found to contain bugs
Examples of undetected errors
– Ariane 5 rocket explosion, 1996 (exception occurred
when converting 64-bit floating number to a 16-bit
integer)
– Pentium bug (multiplier table not fully verified)
– many more ….
Somehow make debugging happen earlier where it is cheaper 13 13

14. Example: 2x4 Binary Decoder
Safety critical system failure could cause human life.
Commercial critical systems: great financial loss if the product is recalled or is found to contain bugs
Examples of undetected errors
– Ariane 5 rocket explosion, 1996 (exception occurred
when converting 64-bit floating number to a 16-bit
integer)
– Pentium bug (multiplier table not fully verified)
– many more ….
Somehow make debugging happen earlier where it is cheaper 14 14

15. Example: 4-to-4 Priority Encoder
Safety critical system failure could cause human life.
Commercial critical systems: great financial loss if the product is recalled or is found to contain bugs
Examples of undetected errors
– Ariane 5 rocket explosion, 1996 (exception occurred
when converting 64-bit floating number to a 16-bit
integer)
– Pentium bug (multiplier table not fully verified)
– many more ….
Somehow make debugging happen earlier where it is cheaper 15 15

16. Common Mistakes! Incomplete Branch not possible
Incomplete Signal Assignment

17. Common Mistakes!
Incomplete Signal Assignment Solution 1

18. Common Mistakes!
Incomplete Signal Assignment Solution 2

19. Outline
If statement
Case Statement
For loop Statement 19 19

20. For-Loop Statement Looping in VHDL Syntax for index in loop_range loop
sequential statements;
end loop;
Safety critical system failure could cause human life.
Commercial critical systems: great financial loss if the product is recalled or is found to contain bugs
Examples of undetected errors
– Ariane 5 rocket explosion, 1996 (exception occurred
when converting 64-bit floating number to a 16-bit
integer)
– Pentium bug (multiplier table not fully verified)
– many more ….
Somehow make debugging happen earlier where it is cheaper 20 20

21. For-Loop Statement – Conceptual implementation
For loop should be treated as “shorthand” for repetitive statements
E.g., bit-wise xor
Safety critical system failure could cause human life.
Commercial critical systems: great financial loss if the product is recalled or is found to contain bugs
Examples of undetected errors
– Ariane 5 rocket explosion, 1996 (exception occurred
when converting 64-bit floating number to a 16-bit
integer)
– Pentium bug (multiplier table not fully verified)
– many more ….
Somehow make debugging happen earlier where it is cheaper 21 21

22. Summary Concurrent statements Sequential statements
Have clear, direct mapping to physical structures
Difficult to represent complex behaviors
Sequential statements
Flexible and versatile
Resulting hardware may not be very straight forward at times
Can be easily abused 22