overview.txt

AT91所有开发板的资料 AT91所有开发板的资料

File:	uHALDemos\docs\overview.txt
	$Id: overview.txt,v 1.1 2000/01/12 16:45:42 mquinn Exp $

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These uHAL Demonstration programs are basic examples which show some of
the functionality and flexibilty of uHAL.

There are two types of demo:
  (a)	Simple tests which prove a piece of functionality.
  (b)	Timing tests which show how an application behaves when
	different caching strategies are used.

Support files are marked with (s).

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(a)	hello.c

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Simple Print Test

This program simply outputs data to the serial port. It is a typical
'early-run' program: one of the first images you might run on a new
target. See io.c and led.c for other minimal examples.

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(a)	io.c

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Simple Input/Ouput Test

This program takes data input on the serial port and echoes it on the
output. It is another typical 'early-run' program.

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(a)	led.c

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LED Flash Test

This program simply flashes the LEDs in a binary pattern. It is a
typical 'first-run' program: one of the first images you might run on a
new target. It requires no additional functionality (such as serial
ports) to be working in order to run. Note: the semihosted version does
print out a banner and description, since this functionality must be
available.

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(a)	heap.c

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Simple Memory Heap Test

Very simple example which shows memory being allocated and free'd.

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(a)	simple-caches.c

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System Cache Example

All this program does is read the cache & MMU state, reset the cache &
MMU, turn caches & MMU on, then off and finally restores the original
state.

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(a)	system-timer.c

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System Timer Test

This program combines serial output and LED flashing with timers and
interrupts. This image combines most of the features of uHAL and is
a good indicator that a new target is usefully functional.

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(a)	file-io.c

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Example File I/O

This program only runs semi-hosted and linked with the C Library. It 
performs some file-io on the host to return the size of the file
specified by the user.

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(a)	exception.c

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Example Exception Handling

This program shows how the C Library handles a divide-by-zero exception.

Note: When building this example, the compiler will display a warning.

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(b)	bubble.c

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Simple Bubble Sort

Sort by comparing each adjacent pair of items in a list in turn,
swapping the items if necessary, and repeating the pass through the
list until no swaps are required. 

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(b)	queens.c

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The Eight Queens Problem 


The problem of the eight queens is a well known example of the use of
recursion and of backtracking algorithms. The eight queens problem is
stated as follows "Eight queens are to be placed on a chess board in
such a way that no queens checks against any other queen". 

One strategy is to guess at a solution. However there are 4,426,165,368
ways to arrange 8 queens of 64 squares; so many ways that it would be
exhausting to check all of them for a solution to this problem.
Nevertheless, a simple observation eliminates many arrangements from
consideration: No queen can reside in a row or a column that contains
another queen. Alternatively, each row and column can contain exactly
one queen. 

The problem can be expanded to numbers greater than 8. uHAL uses 20 so
that a larger data array is exercised.

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(b)	sieve.c

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Sieve of Eratosthenes

An algorithm to find all prime numbers up to a certain N. Begin with an
(unmarked) array of integers from 2 to N. The first unmarked integer, 2,
is the first prime. Mark every multiple of this prime. Repeatedly take
the next unmarked integer as the next prime and mark every multiple of
the prime. 

Note: Invented by Eratosthenes of Cyrene (276 BC - 194 BC). 

For example, here's a beginning array. 

 2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25

Since 2 is unmarked, it is our first prime. We mark every second
integer, that is, 4, 6, 8, 10, 12, etc. 

[2] 3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
       -     -     -    --    --    --    --    --    --    --    --

The next unmarked integer is 3, so it is prime, and we mark every third
integer, i.e., 6, 9, 12, etc. Note that we mark 6, 12, 18, etc. again.

[2][3] 4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
       -     -     -    --    --    --    --    --    --    --    --
       -     -     -  - --    --    -- -- --    --    -- -- --    --

Now 5 is the next prime, and we mark every fifth integer. The only new
integer marked in range is 25. 

[2][3] 4 [5] 6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
       -     -     -    --    --    --    --    --    --    --    --
       -     -     -  - --    --    -- -- --    --    -- -- --    --
       -     -     -  - --    --    -- -- --    --    -- -- --    -- --

From here we find the primes 7, 11, 13, 17, etc. 

To optimize, when we find the prime n, we can begin marking at n2, since
anything less than that is n times a lesser prime, so will have been
marked earlier. As a corollary, we can stop marking when n2 is greater
than our range. That is, any unmarked numbers greater than the square
root of the range are primes. 

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(b)	sieve500.c

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Sieve of Eratosthenes

This is a repeat of the above test, with the main loop unrolled to
guarantee that the instruction cache is ineffective.

This program is not built by default.

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(s)	test.c

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This is a shell which wraps around the timing tests. It uses standard
uHAL routines to determine which cache/MMU features are supported and
calls the test for each state.

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(s)	target.c

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This file contains the routines which handle installation of the timer
and handling of the interrupt. Again, all of these functions use
standard uHAL routines.

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(s)	pr_head.c

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Simply some common routines to print out a banner when a program starts
and when it completes.

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