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| From | Ivan Shmakov <oneingray@gmail.com> |
|---|---|
| Newsgroups | comp.arch.embedded, comp.lang.c |
| Subject | Re: Getting started with AVR and C |
| Date | 2012-11-25 04:18 +0700 |
| Organization | Aioe.org NNTP Server |
| Message-ID | <86boem66on.fsf@gray.siamics.net> (permalink) |
| References | <22t1b8pt63pcb3fks5ic03tsnlnhlm6ef1@4ax.com> |
Cross-posted to 2 groups.
>>>>> Robert Roland <fake@ddress.no> writes:
[Cross-posting to news:comp.lang.c, in the hope that someone
could provide more suggestions, or correct me on C.]
[...]
> 2. Where do I start learning C? Is there a good online tutorial
> somewhere? I'd also be willing to buy a book. Is there one that
> stands out as the best?
Frankly, I don't quite understand how did I learn C myself.
FWIW, there were hardly any good book on that that I've read.
Two aspects of C are probably to be highlighted:
* first of all, unlike some other, and higher-level, languages
(like Pascal, BASIC, etc.), C has a very concise set of
syntactic constructs; most of the power lies in libraries, and
should you end up using AVR Libc, be sure to check its
reference manual [1] (it isn't as good as the GNU C Library
manual I'm using for the most time I need information on C,
but it's still useful);
* the C constructs tend to be translated into assembly in a
rather straightforward manner (unless advanced optimization is
involved, that is); consider, e. g.:
int8_t i; /* not necessarily translated; may force
the compiler to "allocate" a register
(say, r7), or a memory cell */
i = 3; /* ldi r7, 3 */
i += 2; /* adi r7, 2 */
i++; /* inc r7 */
if (i < 9) { /* cpi r7, 9 ; brge else_a */
int8_t j = 5; /* ldi r8, 5 */
while (j >= 3) { /* while_a:
cpi r8, 3
brlt end_while_a */
PORTB ^= 1; /* in r9, PORTB
eoi r9, 1
out PORTB, r9 */
} /* jmp while_a
end_while_a: */
} /* else_a: */
Not to undermine its value, but as could be seen (I hope) from
this example, for the most part, C only manages registers and
memory (including function calling conventions) while the rest
of its /syntax/ is comparable to that of a library of assembly
language macros of some sort.
A cheat sheet for most of the C operators would probably be
something like the following (where a, b, c, ... are either
numeric literals, variable identifiers, or expressions.) Note
that whenever all the operands are integer, an integer operation
is performed. (So, 7 / 3 is 2.) The result is as wide as the
widest of the operands. (So, i + j is 0 if i is 255, j is 1,
and both are declared to be of the 8-bit unsigned integer
uint8_t type.)
Operation Value Side-effect
Operations free of side-effects
+ a a
- a - a
* a the value of the memory cell at address
a
& a the address of a (must be an "l-value")
~ a bitwise negated a
! a 1 if a is 0,
0 otherwise
a, b b
NB: a is evaluated first, its result discarded.
a + b a + b
a - b a - b
a * b a b
a / b a / b (quotient of)
a % b remainder of a / b
a & b a (bitwise and) b
a | b a (bitwise or) b
a ^ b a (bitwise exclusive or) b
a << b a times 2 ^b (shift left)
a >> b a times 2 ^(-b) (shift right)
a < b 1 if a is less than b,
0 otherwise
a > b 1 if a is greater than b,
0 otherwise
a == b 1 if a is equal to b,
0 otherwise
a <= b 1 if a is less than or equal to b,
0 otherwise
a >= b 1 if a is greater than or equal to b,
0 otherwise
Conditional operations
a && b a is evaluated;
if a is non-zero, the value is b;
otherwise, the value is 0, while b is
not evaluated at all
a || b a is evaluated;
if a is zero, the value is b;
otherwise, the value is a, while b is
not evaluated at all
a ? b : c a is evaluated first;
if a is non-zero, the value is b;
otherwise, the value is c;
the other ("unused") expression is not
evaluated
Operations with side-effects
NB: a must be an "l-value"
a++ a a set to a + 1
a-- a a set to a - 1
++a a + 1 a set to value
--a a - 1 a set to value
a = b b a set to value
a += b a + b a set to value
a -= b a - b a set to value
a *= b a b a set to value
a /= b a / b a set to value
a &= b a (bitwise and) b a set to value
a |= b a (bitwise or) b a set to value
a ^= b a (bitwise xor) b a set to value
a <<= b a times 2 ^b a set to value
a >>= b a times 2 ^(-b) a set to value
Naturally, both "=" and "," can be "nested", thus:
for (a = b = 0, c = 5; c > 0; a++, b++, c--) {
/* ... */
}
To note is that the for () <statement> form is just a short-hand
for a specific while () loop. For instance, the for ()
statement above can be rewritten as follows:
a = b = 0, c = 5;
while (c > 0) {
/* ... */
a++, b++, c--;
}
Thus, the only convenience of for () is that it allows for the
"at-the-end-of-the-loop" part to be written above the loop body
itself (i. e., together with the loop condition.)
One more thing to note is that there're two basic contexts: the
statement context, and the expression context. The switch from
the former to the latter usually takes place in obvious places,
while it isn't possible (in standard C; AFAIK) to switch from
the latter to the former. E. g.:
/* statement context */
while (a < 5 /* expression context */) {
/* statement context */
b = 4 /* expression context */ ;
/* NB: cannot switch back to the statement context, like: */
/* c = while (b > 0) { /* ... */ } ; */
}
As one may need a conditional operator in either context, C has
both the ?:-operator (see above), and (perhaps a more
conventional) if ():
if (a) {
/* the code here will be executed iff a is non-zero */
} else {
/* the code here will be executed otherwise */
}
The { }-grouping is only necessary if more than one statement is
needed as the body; otherwise, it may be elided, like:
if (a) b = c;
This allows for convenient nesting, like:
if (a) {
/* ... */
} else if (b) {
/* ... */
} else {
/* ... */
}
A similar idiom is possible for the ?:-operator just as well.
Consider, e. g.:
a = (b ? c
: d ? e
: f);
which is not dissimilar to more verbose (and error-prone):
if (b) {
a = c;
} else if (d) {
a = e;
} else {
a = f;
}
An example program for an AVR could be as follows.
#include <avr/io.h> /* for PORTB, DDRB, etc. */
#include <util/delay.h> /* for _delay_ms () */
/* global variable declarations; not necessary in this example */
static void
blink_led (void)
{
PORTB ^= (1 << PB0); /* toggle PB0 */
_delay_ms (500); /* wait for 0.5 s */
PORTB ^= (1 << PB0); /* toggle PB0 again */
_delay_ms (500); /* wait for 0.5 s more */
}
/* the main () function is the conventional program's entry point */
int
main ()
{
/* set up PB0 for output, all the other tri-stated */
DDRB = (DDRB0 << 1);
/* enter infinite loop */
while (1) {
/* call our function */
blink_led ();
}
/* never reached */
return 0;
}
For sure, there's over than a dozen of individual syntactic
constructs more (and then there's a handful or so of the
preprocessor #-directives, too), but I hope that with the above,
reading the sources would become a bit easier task.
[1] http://www.nongnu.org/avr-libc/user-manual/
--
FSF associate member #7257
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Re: Getting started with AVR and C Ivan Shmakov <oneingray@gmail.com> - 2012-11-25 04:18 +0700
Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-11-24 17:09 -0500
Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-24 22:12 +0000
statement / expression contexts in C Ivan Shmakov <oneingray@gmail.com> - 2012-11-28 12:54 +0700
Re: Getting started with AVR and C Ivan Shmakov <oneingray@gmail.com> - 2012-11-28 13:37 +0700
Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-28 14:49 +0000
Re: Getting started with AVR and C Frank Miles <fpm@u.washington.edu> - 2012-11-28 17:53 +0000
Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-28 18:05 +0000
Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 12:56 -0600
Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-28 21:45 +0000
Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 15:55 -0600
Re: Getting started with AVR and C David Brown <david.brown@removethis.hesbynett.no> - 2012-11-29 01:35 +0100
Re: Getting started with AVR and C Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-11-29 01:47 +0100
Re: Getting started with AVR and C David Brown <david@westcontrol.removethisbit.com> - 2012-11-29 09:24 +0100
Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 01:18 +0000
Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 20:07 -0600
Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:23 +0000
Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 11:01 -0500
Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 19:19 +0000
Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 14:32 -0500
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-29 11:44 -0800
Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 21:23 +0000
Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 18:15 -0800
Re: Getting started with AVR and C upsidedown@downunder.com - 2012-11-29 22:17 +0200
Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 12:36 -0800
Re: Getting started with AVR and C Stephen Sprunk <stephen@sprunk.org> - 2012-11-29 16:22 -0600
Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 18:36 -0800
Re: Getting started with AVR and C "Boudewijn Dijkstra" <sp4mtr4p.boudewijn@indes.com> - 2012-12-11 10:53 +0100
Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-12-11 14:53 +0000
Unicode Ivan Shmakov <oneingray@gmail.com> - 2012-12-14 23:25 +0700
Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-12-15 14:30 -0500
Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-12-15 12:24 -0800
Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-12-15 18:02 -0500
Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-12-15 15:45 -0800
Re: Getting started with AVR and C Richard Damon <news.x.richarddamon@xoxy.net> - 2012-12-16 22:55 -0500
Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-12-16 23:20 -0800
Re: Getting started with AVR and C Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-12-17 12:27 +0200
Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-12-17 11:17 +0000
Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-12-17 14:07 +0000
Re: Getting started with AVR and C Nobody <nobody@nowhere.com> - 2012-12-16 03:28 +0000
Re: Getting started with AVR and C upsidedown@downunder.com - 2012-12-16 10:40 +0200
Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 02:31 +0000
Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 03:36 +0000
Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 03:55 +0000
Re: Getting started with AVR and C David Brown <david@westcontrol.removethisbit.com> - 2012-11-29 09:37 +0100
Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 11:31 +0000
Re: Getting started with AVR and C David Brown <david@westcontrol.removethisbit.com> - 2012-11-29 13:44 +0100
Re: Getting started with AVR and C Hans-Bernhard Bröker <HBBroeker@t-online.de> - 2012-11-29 13:22 +0100
Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 13:32 +0000
Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 11:28 -0800
Re: Getting started with AVR and C Ben Bacarisse <ben.usenet@bsb.me.uk> - 2012-11-29 13:20 +0000
Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 09:07 -0500
Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 09:17 -0500
Re: Getting started with AVR and C pete <pfiland@mindspring.com> - 2012-11-29 18:25 -0500
Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 22:46 -0500
Re: Getting started with AVR and C lawrence.jones@siemens.com - 2012-11-30 11:47 -0500
Re: Getting started with AVR and C Tim Rentsch <txr@alumni.caltech.edu> - 2012-12-17 03:53 -0800
Re: Getting started with AVR and C Keith Thompson <kst-u@mib.org> - 2012-11-29 11:38 -0800
Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 15:21 -0500
Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-28 22:26 +0000
Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 17:32 -0600
Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 19:02 -0500
Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 18:29 -0600
Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 23:39 -0500
Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.please> - 2012-11-29 00:59 -0600
Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 07:57 -0500
Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-29 13:02 -0600
Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:19 +0000
Re: Getting started with AVR and C Phil Carmody <thefatphil_demunged@yahoo.co.uk> - 2012-11-29 12:03 +0200
Re: Getting started with AVR and C glen herrmannsfeldt <gah@ugcs.caltech.edu> - 2012-11-29 11:39 +0000
Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-29 08:04 -0500
Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:17 +0000
Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 19:19 -0600
Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 23:44 -0500
Re: Getting started with AVR and C James Kuyper <jameskuyper@verizon.net> - 2012-11-28 13:15 -0500
Re: Getting started with AVR and C Arlet Ottens <usenet+5@c-scape.nl> - 2012-11-28 19:17 +0100
Re: Getting started with AVR and C Tim Wescott <tim@seemywebsite.com> - 2012-11-28 19:30 -0600
Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 15:29 +0000
Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-11-29 16:36 +0000
Re: Getting started with AVR and C upsidedown@downunder.com - 2012-11-29 22:40 +0200
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-29 13:55 -0800
Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 22:06 +0000
Re: Getting started with AVR and C Jon Kirwan <jonk@infinitefactors.org> - 2012-11-29 14:22 -0800
Re: Getting started with AVR and C Grant Edwards <invalid@invalid.invalid> - 2012-11-29 21:59 +0000
Re: Getting started with AVR and C John Devereux <john@devereux.me.uk> - 2012-11-30 08:29 +0000
Re: Getting started with AVR and C Nick Keighley <nick_keighley_nospam@hotmail.com> - 2012-11-25 05:41 -0800
Re: Getting started with AVR and C Rosario1903 <Rosario@invalid.invalid> - 2012-11-27 10:21 +0100
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