[avr-gcc-list] sdram adress/length
hello all, i am using avr-gcc (GCC) 3.4.3, and using ATmega16 , and writng the code for copying sdram data int flash, in c language. There are three address bytes and three length bytes for sdram. At a time i can read 16 bytes from sdram, then i want to decerment the length and incerement the address value bye 16. how to increment address value(or decrement the length), by using a single variable. i dont want use three different bytes, because then propogating carry becomes a problem.. is there any way , by which we can define a data type which takes three bytes of memory...? or how can i solve this problem? regards,varsha-- ***Confidentiality Notice*** The information contained in this electronic message and any attachments to this message are intended for the exclusive use of the addressee(s) and may contain confidential or privileged information. If you are not the intended recipient, please notify the sender at Divinet or [EMAIL PROTECTED] immediately and destroy all copies of this message and any attachments. ___ AVR-GCC-list mailing list AVR-GCC-list@nongnu.org http://lists.nongnu.org/mailman/listinfo/avr-gcc-list
[avr-gcc-list] V.43 fax
Is there anyone who develope V.34 fax communicationwith AVR using single modem ? Andi ___ AVR-GCC-list mailing list AVR-GCC-list@nongnu.org http://lists.nongnu.org/mailman/listinfo/avr-gcc-list
Re: [avr-gcc-list] AVR assembly for fast bit bang
I suspect you misunderstand what optomization means, especially when
applied to a small microcontroller. Choosing -Os (or -O2, which is very
similar) tells the compiler to generate small and fast code. It is not
dangerous or risky. Gcc does have a few risky optomisation passes that you
can explicitly enable - it always has cutting-edge features that have not
had enough testing to be considered safe enough for -O2 level. But choosing
to run gcc with -O0 will cripple your code as gcc tries to use the most
obvious code for each individual statement with a total disregard for
context or the features of the target processor. It even turns off much of
the warning features of gcc (enabled by -W and -Wextra), since they share
the same code analysis. Very occasionally, it can be of interest to use
only -O1 optomisation in connection with debugging or viewing generated
assembly code. But normally -Os is the right optomisation for common use.
And if your code works without optomisation but fails when -Os is used, then
you can be 99% sure it is your code that is at fault. Optomising with -Os
is almost always a far better idea than optomising by writing your own
assembly.
And don't forget, TI's DSPs (at least the 320F24x family I have used) are
horrible processors with vastly over-priced and buggy tools. Don't tar
avr-gcc with the same brush.
Having said that, the main causes of slowness in your code is because you
haven't really thought about what you are asking the compiler/cpu to do, and
how you expect it to do it. In particular, you have a (1 n) expression
inside the loop. This gives your code an O(n^2) complexity instead of O(n).
Either shift your data one bit each loop, or use a mask variable that you
shift one bit each loop. As it stands, this expression will probably cause
a library function call in -O0 (it's probably inlined with -O2) for a huge
unnecessary overhead.
Secondly, you are using 16-bit data unnecessarily. As a rule of thumb,
using 16-bit data takes three times as long as 8-bit data on the AVR.
Re-organize the code to send two 8-bit bytes for much faster code.
mvh.,
David
- Original Message -
From: Mike S. [EMAIL PROTECTED]
Hello to all,
My code is:
#define ADS1210_PORT PORTF
#define SDIO_BIT 0x04 /* 0b 0100 PORTF.2*/
#define CLK_BIT 0x02 /* 0b 0010 PORTF.1*/
#define SDOUT_BIT0x01 /* 0b 0001 PORTF.0*/
#define SDIO_LOWADS1210_PORT = ~SDIO_BIT
#define SDIO_HIGH ADS1210_PORT |= SDIO_BIT
#define CLK_LOW ADS1210_PORT = ~CLK_BIT
#define CLK_HIGH ADS1210_PORT |= CLK_BIT
/*--
--+
| Function: write_data
|
|
|
| Args: n_bits
|
|
|
| Action: Writes n_bits in the device SDIO input pin
|
|
|
| Efects:
|
|
|
+---
-*/
void write_data (Word towrite, Byte nbits)
{
Byte n;
for(n = 0; n nbits; n++)
{
CLK_HIGH;
if( towrite (0x0001 n))
{
SDIO_HIGH;
}
else
{
SDIO_LOW;
}
CLK_LOW;
}
}
I haven't decided yet if I will use the AT90CAN128 SPI module or do it
by bit bang! My uC runs at 16MHz. The device I'm interfacing with
supports serial clock rates up to 2 MHz. In the past, I already made a
driver for this device for the Philips XA-S3 in C and in Assembler
(the asm was for the bit bang part), and now I want to port that
driver to the AVR. The problem is that I don't have a lot of
experience with the AVR assembly! That is why I'm asking this question
(wrong guess David Kelly, but thanks for the reply). BTW, is your code
snippet correct?
Thanks for the reply Daniel O'Connor, but I usually don't use the
optimization until I try a couple of and optimization techniques. I
already had some bad experiences with the optimization in some Texas
Instruments DSPs...
I use AVR-GCC.
Thanks to all replies.
Thanks in advance
Bruno Miguel
On 11/9/05, David Kelly [EMAIL PROTECTED] wrote:
On Tue, Nov 08, 2005 at 03:45:54PM +, Mike S. wrote:
Hello to all,
Can anyone tell me the best (faster) way to implement bit shifting
(serial synch protocol -in a bit bang fashion-) with two general
purpose digital pins (one pin for data the other for clock)? Using C
is not fast enough! I need assembly!
Sounds like a homework assignment. Smart instructors monitor this list.
People keep saying C isn't fast enough. I don't belive it. First
attempt:
#include avr/io.h
#define CLOCK_B (10)
#define BIT_B (11)
void
myjunk(uint8_t byte) {
uint8_t i;
for( i = 0 ; i 8 ; i++ ) {
PORTA |= CLOCK_B; // rising edge of clock
if( byte (17) )
PORTA |= BIT_B; // set
else
PORTA = ~BIT_B;// clear
byte = 1;
PORTA = ~CLOCK_B; // falling edge of clock
}
}
Compiled with
RE: [avr-gcc-list] sdram adress/length
From: varsha [EMAIL PROTECTED]
hello all,
i am using avr-gcc (GCC) 3.4.3, and using ATmega16 ,
and writng the code for copying sdram data int flash, in c language.
There are three address bytes and three length bytes for sdram.
At a time i can read 16 bytes from sdram, then i want to decerment the
length and incerement the address value bye 16.
how to increment address value(or decrement the length), by using a single
variable.
i dont want use three different bytes, because then propogating carry
becomes a problem..
is there any way , by which we can define a data type which takes three
bytes of memory...?
Obviously, you could use unsigned long, which solves all your problems at
the cost of one unused byte. Each.
unsigned long sdram_adr = 0;
unsigned long sdram_len = 0x100;
while (sdram_len 0)
{
process_16_sdram_bytes(sdram_adr);
sdram_len -= 16;
sdram_adr += 16;
}
However, access to unsigned long is not atomic. If you are going to be
accessing these values in interrupt service routines, you'll have to protect
access in mainline code so they aren't interrupted.
Hope this helps,
-=Dave
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Re: [avr-gcc-list] sdram adress/length
(Please post in plain text format, not tiny font html) You can use unsigned long int (or uint32_t) for 32-bit unsigned integers. I don't think there is any support for three-byte data in avr-gcc - it is not a commonly used size in C. You'll waste a little time and space with 32-bit data, but it will save worrying about the carry. Alternatively, and probably better, you could re-organize your loops in terms of inner and outer loops with (at most) 16-bit counters for each. Of course, flash write speed is by far the overhead in such a loop, not the calculation of the increments. And are you sure you mean sdram? I can't think of any way an sdram chip could be connected to an AVR and still work properly. You've got to access it synchronous to a fast clock, and refresh the data regularly. mvh., David - Original Message - From: varsha hello all, i am using avr-gcc (GCC) 3.4.3, and using ATmega16 , and writng the code for copying sdram data int flash, in c language. There are three address bytes and three length bytes for sdram. At a time i can read 16 bytes from sdram, then i want to decerment the length and incerement the address value bye 16. how to increment address value(or decrement the length), by using a single variable. i dont want use three different bytes, because then propogating carry becomes a problem.. is there any way , by which we can define a data type which takes three bytes of memory...? or how can i solve this problem? regards, varsha -- ___ AVR-GCC-list mailing list AVR-GCC-list@nongnu.org http://lists.nongnu.org/mailman/listinfo/avr-gcc-list
