Pi GPIO in RISC O/S

Can I ask a really simple question?
I want to write a relatively simple program on a Pi in RISC OS BASIC which uses the GPIO pins. Can I read from and write to the pins from RISC OS and if so, how? Can it also talk to a GertBoard?

I want to write a relatively simple program on a Pi in RISC OS BASIC which uses the GPIO pins

Use the GPIO module. It is in ROM. For example:

SYS "GPIO_ReadMode",27 TO pin27%
IF (pin27% AND &1F)<>0 THEN ERROR 0,"GPIO 27 is not in GPIO (0) mode"
SYS "GPIO_WriteOE",27,1:REM set GPIO27 to input
SYS "GPIO_ReadData",27 TO a%
SYS "GPIO_WriteMode",27,&60:REM set GPIO27 pull high
SYS "GPIO_ReadData",27 TO b%
PRINT "GPIO 27 defaults to pulled low so a% is read as ";a%;" s.b. 0"
PRINT "then reads as ";b%;" s.b. 1 after pull up status changed to up."

Chris
Thank you for your very quick reply. I tried running the lines you gave me but all I got was “SWI unknown” messages. I am not sure what version of RISC OS I have as I have not used it for a very long time so I will install your latest version then try again. Do you know anything about combining a Pi, RISC OS and add-on boards such as the Gertboard?

Just go to the command line or open an command window ( use F12 or Crtl – F12 ) and type FX 0 . Or look at info in the RO icon on the bar on the right side

Thank you Timo. I have Version 5.21 dated July 2013
How can I find what SYS commands I have in ROM. Do I need to do anything to put them there?
I am coming back to RISC programming after a very long time and do not recall using these functions before.

I have Version 5.21 dated July 2013

The GPIO module wasn’t added to RISC OS until 2014.

I suggest you download the latest stable release of RISC OS and write it to a new SD card: the easiest way of doing this is to use Raspberry Pi Imager – select “RISC OS” as the operating system.

Thank you Stuart. It solves that issue. I’ll reload with the current version of RISC OS.

My SD card with 5.28 arrived this morning and I installed it in my Pi. Opening Utilities.!Manual.Root showed that there are now entries for GPIO. Excellent. Opening the GPIO primer appeared to give me step by step instructions of how to use it. Excellent. However, the first step is “check the module is loaded”, with some alternative ways of finding out. I assumed everything associated with the OS is on the card I just bought and was loaded as part of the OS. Can you tell me what is “the module”, where do I find it and how do I load it? It might be a good idea to add these missing details to the manual.

In 5.28 the module is standard available. The text from the primer needs some updating ;-)

In 5.28 the module is standard

Here it’s the last ROM module, number 136, as displayed by Verma, though the internal web link for that appears to be broken.

A quick search finds it here

Lenny seems to have changed his index page!

*modules here on rPi shows it at number 128, RO5.28

*modules here on rPi shows it at number 128, RO5.28

Sorry, mine’s 5.29.

A quick search finds it here

Wow, who made that mess? Looks like the zip might have been created on a Mac (a subfolder in archive root called __MACOSX with metadata within is a clue!) , hence no filetypes at all.

Types are:

!Boot / !Run – &FEB
!Help / Messages – &FFF
!RunImage – &FF8
!Sprites / !Sprites22 / Sprites – &FF9
Templates – &FEC

Note – if setting the type via Filer, you can drop the leading ‘&’ and it’ll still work.

Wow, who made that mess?

Opened a can of worms there, didn’t I! And I was only trying to be helpful!

My archived archive is fine!

Thanks Timo, I still cannot find !GPIOMachine but the code that Chris Hall sent me now runs, so I guess all is well.

Thank you all for your help.

You seem to drifted off the subject a bit. Based on what Chris sent me a while ago and the information in the StrongEd guide, I expected to be able to do what I want, but I am still lost. There is lots of information but it just confuses. All I want to do is set a number of pins up so I can switch them off and on, and set another couple pins so that I can read whether they are on or off from an external source.

Could some kind soul help this senile old codger and write down the syntax for the 6 read and write SYS commands that seem to be associated with trying to do this. Prior to trying to use RISC OS for my project, I had used “Return to Basic” which does the same thing in a wonderfully simple way.

Incidentally, whenever I log into this site, it rejects my password, though I know it is right. Does anyone else have this problem?

Try this:

           REM Initialise
   47470 : gpio%=TRUE
   47510 : LOCAL ERROR
   47520 : ON ERROR LOCAL gpio%=FALSE
   47530 : IF gpio% THEN SYS &58FAF:REM Older GPIO modules error here
   47540 : REM Set GPIO 22 to outout high to enable GPS
   47550 : REM Set pins GPIO 16,19,20,21,26,27 to inputs
   47560 : IF gpio% THEN
   47570 :   SYS "GPIO_WriteData",22,1:REM Set pin 22 to HIGH
   47580 :   SYS "GPIO_WriteOE",22,0:REM set pin 22 to output
   47590 :   SYS "GPIO_WriteData",4,1:REM Set pin 4 to HIGH
   47600 :   SYS "GPIO_WriteOE",4,0:REM set pin 4 to output
   47610 :   PROCgpio(16,0,1):REM input
   47620 :   PROCgpio(19,0,1):REM input
   47630 :   PROCgpio(20,0,1):REM input
   47640 :   PROCgpio(21,0,1):REM input
   47650 :   PROCgpio(26,0,1):REM input
   47660 :   PROCgpio(27,0,1):REM input
   47670 : ENDIF
           IF gpio% THEN SYS "GPIO_ReadData",16 TO pin16%:REM read GPIO 16
         :
   47671 : DEFPROCgpio(pin%,data%,oe%)
   47672 : SYS "GPIO_ReadOE",pin% TO old%
   47673 : SYS "GPIO_WriteData",pin%,data%
   47674 : SYS "GPIO_WriteOE",pin%,oe%
   47675 : ENDPROC

Can you tell me what is “the module”, where do I find it

Try here (it’s the last module listed in the ROM).

I’ve setup a wiki page.

Please can someone tell me if it works on Pi 4 or Pi 400? I still am not clear whether GPIO is possible at all on those!

Please can someone tell me if it works on Pi 4 or Pi 400? I still am not clear whether GPIO is possible at all on those!

Broadly, GPIO works on the Pi4/Pi400 if you’re flashing LEDs etc., but the GPIO_WriteMode SWI doesn’t appear to allow you to change from GPIO (default) to another mode eg. PWM.

On the Wiki page you refer to GPIO pins rather than GPIO numbers. It’s confusing, but GPIO 25 is not pin 25 but pin 22. As the GPIO module works from GPIO number rather than pin number, it might be sensible to refer to GPIO numbers rather than pins. There’s lots of diagrams out there showing physical pin number and GPIO number too, hopefully one of them will have a suitable licence to allow it to be either copied or linked from the Wiki.

It’s confusing

It is :-/

I’ve tried to square the BCM2835 peripherals table up with GPIO_Info, but I can’t match it up.
For example on logical pin 0, GPIO_Info gives me modes available GPIO, I2C, SPI, UART, I2C. The table on the other hand says

GPIO0
ALT0 : SDA0
ALT1 : SA5
ALT2 : reserved
ALT3 : 
ALT4 :
ALT5 :

There’s not even the same number of modes :-(

We could link to this, but again I don’t understand how the alternative function information relates to what the GPIO module says.

You have to look at the Legacy section of the StrongHelp Manual to find what the mode numbers for Read/WriteMode mean:
0 = GPIO Input
1 = GPIO Output
2 = Alt 5
3 = Alt 4
4 = Alt 0
5 = Alt 1
6 = Alt 2
7 = Alt 3

and then look at the BCM2835 (or whatever Pi you have) to see what each Alt mode corresponds to for each GPIO! eg. alt 0 (so Mode 4) for GPIO 12 & 13 is PWM, which redirects the audio PWM signal to GPIO 12/13 instead of to the headphone socket, or at elast it does on earlier Pi’s, it appears to be broken on the Pi4/400 under RISC OS (I can do it from RaspberryPi OS).

I found the Pi 3 modes were fixed in August, so I need to use a newer HAL.

Thank you again Chris. Is there any reason why you have written a PROC for inputs but not outputs?

Thank you to everyone else for your contributions

Andrew, if you use Return To Basic there is another set of pin numbers associated with WiringPi, just to confuse you some more.

Andrew, if you use Return To Basic there is another set of pin numbers associated with WiringPi, just to confuse you some more.

Yes, I’ve seen those, but prefer not to mention them so I might forget they exist! How many numbering schemes do we need?

there is another set of pin numbers

That’s probably the first time in years that I’ve seen “pin numbers” used in a non-tautological context.

On topic, it seems like people are describing the re-arrangement of GPIO pin use on Pi boards as an almost random item. Why isn’t everything the same on every model of Pi?