Propeller C - high() or low() changes direction, and input() function not recognized?
samuell
Posts: 554
Hi,
I've been experimenting with SimpleIDE to toggle some pins. What I noticed is that high() or low() set the pins to outputs, which is unsafe if they were inputs and a mistake was made. Also, the input() function is not recognized. I'm including simpletools.h.
What I propose is a change of paradigm, as used in other micro-controllers:
I've been experimenting with SimpleIDE to toggle some pins. What I noticed is that high() or low() set the pins to outputs, which is unsafe if they were inputs and a mistake was made. Also, the input() function is not recognized. I'm including simpletools.h.
What I propose is a change of paradigm, as used in other micro-controllers:
//Fuction prototypes
_Bool getlat(unsigned char)
_Bool getpin(unsigned char)
void setpin(unsigned char, _Bool)
void togpin(unsigned char)
_Bool getlat(unsigned char pin) // Gets the value written to the output latch of the pin
{
return (_OUTA & 1 << pin) != 0;
}
_Bool getpin(unsigned char pin) // Gets the value at the pin
{
return (_INA & 1 << pin) != 0;
}
void setpin(unsigned char pin, _Bool val) // Sets the output pin to the given value
{
if (val != getlat(pin)) // Notice that we are comparing to the latch, not actually reading from the pin
togpin(pin);
}
void togpin(unsigned char pin) // Toggles the output pin
{
_OUTA ^= 1 << pin;
}
This code wasn't thoroughly tested, but it should work. The idea is that one should set the pin direction previously, and explicitly, before using them. Although usually used on input pins, getpin() makes sense if used on output pins, if we want to see if the pin is not shorted.
Comments
I'm 100% with you on your opinion here. However, the author of the Simple libraries was perfectly aware what he was doing, and surely meant to write the functions exactly as they are written. I believe the choice was between simplicity and flexibility, and he went with simplicity. So much of Parallax's revenue comes from education (and that is the primary goal of SimpleIDE and the Simple libraries) that simplicity outweighed the consequences you outline above.
Note sometimes for intercog communication I use the get_state() function for one cog to read the output pin state set by another cog.
Tom
As for the simplicity motive, it might lock people to a mindset. I see it happening with Arduino. It happened myself when I refused to learn C/C++ due to the simplicity of Euphoria.
if (condition == true) high(pin); else low(pin);instead of just It is unnecessary to use two separate functions for the same thing with different values, IMHO. But two extra functions won't hurt either.By the way, the get_state() and get_states() functions read from _INA or from _OUTA? One thing is reading from the actual pin, other is reading from the output latch. If the output pin is forced the values might not match. Conversely get_output() and get_outputs() use what register? Also, does set_output() and set_outputs() set the direction to outputs? There is no documentation regarding these specificities. In the end, I could have used those functions, but the lack of documentation was what lead me to create the alternatives, because I didn't even knew about them, and yet I'm to learn about the specifics. Sorry, but such lack of documentation is appalling.
All other standard C functions were not a problem to me, because I can use other sources. I already had such conundrum when wanting to use lockset(), locknew(), lockclr() and cogstart(). Names are not intuitive and documentation is not very clear. Same as for these, because one has an hart time to understand what reads from the pins (e.g. _INA) and what reads from the latch (e.g. _OUTA). Proper naming is advised. My suggestion:
- Keyword "input" only if the function sets the direction to input;
- Keyword "output" only if the function sets the direction to output;
- Keyword "pin" if the function reads from the pins (but OK if it writes to the latch);
- Keyword "latch" if the function reads from the output latch.
As for having to create custom functions when I probably didn't have to, oh well, at least my little test program is compatible with any lib version.
Kind regards, Samuel Lourenço
And Parallax does not recommend SimpleIDE or the Simple libraries for production use
However, you may enjoy PropWare if you're willing to give C++ a shot. I developed it with more complicated programs in mind, and where you need better flexibility. The Pin class has a few different constructors, one of them takes a pin mask and direction.
Kind regards, Samuel Lourenço
The Simpletools library version I mentioned is the latest.
Not sure if this helps, but this is what the library says:
The function takes 2 parameters:
void set_output ( int pin, int state ) Set I/O pin output register bit to either 1 or 0. This function focuses on the I/O pin's output register. If you intend to use it to send high or low signals, consider using high or low functions. This function can also be used in conjunction with set_direction to send high or low signals. Parameters pin I/O pin to set high or low. state 1 for high, 0 for low (when pin is actually set to output, which can be done with setDirection.lockset and the other functions/defines are in the propeller.h library. The documentation is terse, and it would be more useful if it was expanded. The propeller.h library is a lower level library and the functions/defines are essentially analogous to the commands/registers in Spin. For example the dira define is used to load the dira register for the cog with the 32 bit mask. (DIRA = int IO_direction_pin_mask;). The biggest problem I had when using these was understanding how to use the register aliases. Once I read up on them in the propeller manual it became clearer. So yes some more detailed documentation (or at least pointers to other documentation would be very useful, particularly since the propeller.h functions/registers work faster than the Simpletools versions.
Tom