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Changeable PIN name

 
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respected



Joined: 16 May 2006
Posts: 79

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Changeable PIN name
PostPosted: Thu Nov 23, 2017 6:28 am     Reply with quote

Hi;

i want to write driver code. But something is wrong.

output_bit(pin, shift_right(&data,1,0));

This line has problem. Other lines are good. There is no problem.
When i change pin as below, it is OK.

Where is problem?

output_bit(PIN_A0, shift_right(&data,1,0));

Code:
void onewire_reset(int16 pin)
{
output_low(pin);
delay_us( 500 );     
output_float(pin);
delay_us( 500 );       
output_float(pin);
}
   
                                                                             
void onewire_write(int data,int16 pin)
{                                                         
int count;
for (count=0; count<8; ++count)
{
output_low(pin);
delay_us( 2 );
output_bit(pin, shift_right(&data,1,0));
delay_us( 60 );
output_float(pin);
delay_us( 2 );                                                 
}
Ttelmah



Joined: 11 Mar 2010
Posts: 12512

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PostPosted: Thu Nov 23, 2017 7:25 am     Reply with quote

The code will compile as posted. Nothing wrong from that point of view. But it hasn't got a hope of working. The problem is _time_. Onewire is a timing critical bus. Using a variable as a pin name, massively slows down the I/O function. A bit set or clear on a pre-defined pin, is a single assembly instruction. One using a variable for the on/off immediately takes about four instruction times. The shift adds a few more, but using a variable for a pin name, takes it up to using several dozen instructions. It has to actually calculate the bit offset needed, and extract the register address for every single operation.
Being too generic here just destroys the possibility of getting the timings to work.

Have a look at this thread where the basics of changing the functions to support more than one pin were discussed:
<http://www.ccsinfo.com/forum/viewtopic.php?t=36953&highlight=onewire+variable+pin>

It is actually possible to code it in a different way, by extracting the register and bit number just once at the start of the loop. Only worth doing this though if you needed to access a lot of pins. The version shown in the thread above is much simpler.
Mike Walne



Joined: 19 Feb 2004
Posts: 1706
Location: Boston Spa UK

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PostPosted: Thu Nov 23, 2017 7:26 am     Reply with quote

How does the compiler KNOW which pin to operate on for these lines?

Quote:
Code:

output_low(pin);
.
.
.
output_float(pin);
.
                                   


Mike
Ttelmah



Joined: 11 Mar 2010
Posts: 12512

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PostPosted: Thu Nov 23, 2017 7:50 am     Reply with quote

'pin' is a variable he is passing to the function. This will work, but the time involved is far too long to be used for OneWire....
temtronic



Joined: 01 Jul 2010
Posts: 5752
Location: Greensville,Ontario

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PostPosted: Thu Nov 23, 2017 8:07 am     Reply with quote

As others have said Dallas One wire protocol is very 'time sensitive' !
The easy way, the 'cheat', the way I did it was to just copy the 'one wire' driver 4x ,renaming variables as required to control the 4 pcs of DS18B20s temperature devices for a greenhouse controller project.

While 'one wire' does allow 'daisy chaining' of multiple devcies on one bus,since the sensors were 'all over' the greenhouse , it was far simpler to have a 2pole connector for each and dedicate a pin per device.

Code space is not an issue, PICS have tons of memory these days.

Jay
newguy



Joined: 24 Jun 2004
Posts: 1442
Location: Edmonton, Alberta

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PostPosted: Thu Nov 23, 2017 8:34 am     Reply with quote

temtronic wrote:
Code space is not an issue, PICS have tons of memory these days.


You'll be lamenting your PIC's lack of resources if you write an NMEA 2000 compliant CAN driver. Laughing
respected



Joined: 16 May 2006
Posts: 79

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PostPosted: Thu Nov 23, 2017 8:35 am     Reply with quote

I don't want to use this. But I think the only way to do this


Code:
#define ONE_WIRE_PIN1 PIN_A0   
#define ONE_WIRE_PIN2 PIN_E1   
#define ONE_WIRE_PIN3 PIN_A5   
#define ONE_WIRE_PIN4 PIN_B1 
/////////////// 11111111111111111111111111111////////////////////////
void onewire_reset1()

{
output_low(ONE_WIRE_PIN1);
delay_us( 500 );
output_float(ONE_WIRE_PIN1);
delay_us( 500 );     
output_float(ONE_WIRE_PIN1);
}   

void onewire_reset2()

{                               
output_low(ONE_WIRE_PIN2);
delay_us( 500 );     
output_float(ONE_WIRE_PIN2);
delay_us( 500 );       
output_float(ONE_WIRE_PIN2);

.
.
.
temtronic



Joined: 01 Jul 2010
Posts: 5752
Location: Greensville,Ontario

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PostPosted: Thu Nov 23, 2017 8:43 am     Reply with quote

Yes, that's what I did several years ago. As I said it's a clean, simple and it works. It's also very easy to use 'find/replace' to make copies of the driver.
I used 'OW' for 'one wire' as I'm a terrible typist.
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