jensgrabner / digitalwritefast Goto Github PK

What steps will reproduce the problem?
1. Code :
[code]
digitalWriteFast(MY_PIN, HIGH);
digitalWriteFast(MY_PIN, LOW);
[/code]

in my case, MY_PIN was set to 28.

2. Build flags
Use -O3 for optimized code

What is the expected output? What do you see instead?
The expected output would a pulse on the PIN. Instead, the code is purely and 
simply removed by the optimizer. This is expected since the 2nd statement 
"cancels" the 1st one, and the optimizer can see that.
In order to fix this, one should add the "volatile" keyword in the 
"digitalWriteFast" macro definition (instead of casting to uint8_t* the cast on 
line 134 should be to "volatile uint8_t*). This keyword tells the optimizer 
that the referenced variable has a "meaning" outside of the program (i.e. it 
can be modified by an external source, or its modifications affect the outside 
world). It is a good practice (if not mandatory) to add this keyword to 
anything that act as a register.
By the way, the macro _MMIO_BYTE in sfr_defs.h:128 uses volatile : the problem 
actually resides in the cast, which removes it.

The modification was successfully tested.

the fix should be added to the following macros :
-pinModeFast
-digitalWriteFast
-noAnalogWrite
-digitalReadFast (not sure : there is no cast here, so the keyword from 
_MMIO_BYTE is not removed)

What version of the product are you using? On what operating system?
avr-gcc (Fedora 4.7.2-1.fc17) 4.7.2

Please provide any additional information below.
Great work on this library!

By the way, I use it for 8 bit parallel transfers. So I added some macros 
(digitalWriteFastPort, portModeFast, digitalReadFastPort) which make those 
8-bit reads in 1 single instruction : this may be a good addition to your 
library. The only constraint on this is that the user must ensure that its 8 
IOs are on the same port, but it allows a rather fast communication.

Frederic.

The project is all set up for SVN, yet the repository seems to be empty.
Why is this project not under SVN control? 
That way everyone can see an track the changes.

is there any way to make #define'd pins under your library?

for example;

#define DAT_PIN = 21

wouldn't this be the same as; fastDigitalWrite(21,LO)?

#define sclk 52
      digitalWriteFast(sclk, HIGH);
    12c6:   85 b1          in   r24, 0x05   ; 5
    12c8:   82 60          ori   r24, 0x02   ; 2
        asm volatile("nop \n\tnop \n\t");
    12ca:   00 00          nop
    12cc:   00 00          nop
      digitalWriteFast(sclk, LOW);   
    12ce:   8d 7f          andi   r24, 0xFD   ; 253
    12d0:   85 b9          out   0x05, r24   ; 5

after much research, this issue is that the __atomicWrite__ function is missing 
volatile casts on the first parameter to bitWrite which is causing the compiler 
to do various optimizations.  

Attached is a correct version of the code.  I've removed the (uint8_t*) casts 
in the digital macros and just placed them in the atomicWrite macro

WProgram.h is no longer in Arduino 1.0. 

The following change for header files seems to work on 0022 and 1.0.

#if ARDUINO >= 100
#include <Arduino.h>
#else
#include "WProgram.h" 
#include <wiring.h>
#endif

Attempt to use DigitalReadFast on an Arduino Leonardo 

Line using digital read fast, which compiles on Uno..
  if (digitalReadFast(HomeSwitch) == HIGH){ 
gives error
'TCCR2A' was not declared in this scope
'COM2A1' was not declared in this scope
and so on.


Using Windows 7, Arduino 1.5


Thinking that this may have something to do with the different port mappings on 
the Arduino Leonardo and not having updates to this library.