GPIO and BBC Basic

I have searched the BBC Basic manual for various terms which I hoped would allow me to read the GPIO pins on my Pi but cannot find anything.
I know they can be accessed from python so I am guessing this means I will need a bit of assembly code to get readings but I have no idea where the pins can be accessed so could someone give me a pointer please?
tia

see: http://www.riscosopen.org/forum/forums/5/topics/1445
and http://www.tankstage.co.uk/software.html

and to plug a program I made: http://www.egel.org/drupal/software/RISC_OS LedBorg

Thanks Wouter That will surely get me started.

There’s also some info on the r-pi forum: http://www.raspberrypi.org/phpBB3/viewtopic.php?f=55&t=22250

I started converting the Gertboard demo programs to BASIC, but haven’t made great progress so far. What I have can be found at http://www.ronketti.org.uk/ if you’re interested. I’ve reached a bit of a stopping point now with the motor control stuff, as I need to utilise PWM, and for that, I need greater than the centisecond precision that BASIC allows. So, I guess I need to learn ARM assembler – which is a Good Thing to do anyway, so I may as well get on with it.

Ta,

Somewhere I read that you could go into supervisor mode and do short amounts of work. So I tried to do that with the SWI OS_EnterOS and OS_Exit. Nothing happened. What am I doing wrong?

With the arm2008 toolchains GNU assembler: To turn on an LED on pin#17 all one has to do is write a 1 to bit 21 of Pi GPIO base+4. Next, write a 1 to bit 17 of Pi GPIO base +40.

My code uses A% as base address &20200000. B% is 1 written to bit 21 of R1, and C% is 1 written to bit 17.

Here’s my code on the Pi running RISCOS. It goes into assembly and exits but nothing happens to the LED on pin #17. If I use Tank’s module I can get the LED to light up so I know it works, just not with my code.

What am I doing wrong?

10 REM > ASM
20 DIM code% (100)
30 FOR pass =0 TO 3 STEP 3
40 P%=code%
42 A%=&20200000
44 B%=&200000
46 C5=&20000
50 [
60 OPT pass
70 .start
80 SWI &“OS_EnterOS”
100 STR R1, [R0,#4]
110 STR R2, [R0,#40]
190 SWI “OS_LeaveOS”
195 MOV PC, R14
196 NEXT pass
200 CALL start
210 PRINT "On exit R0 is "; USR
300 END

Yes, I could use Tank’s module as it works well but I want to be able to do this with a few lines of assembly code. Tank’s GPIO is a Swiss army knife with error checking. I want to be able do what I’ve done using another assembler. Being a retired photographer and non-programmer, being able to work in BASIC appeals to me.

I was able to use arm2008q3 assembly language to control GPIO pins for a project, http://www.faircloth.org/blog1/?p=7319, and want to be able to do the same time with BASIC with assembly routines. The routines are listed here, http://www.faircloth.org/blog1/?p=7337

If I can just get ove the initial hump using the RISCOS assembler, I may be on my way:)

@ EW Faircloth

The GPIOs are memory mapped under Risc OS. That means you can’t access the BCM2835’s registers directly (which is what your code tries to do). You first need to find out what memory location Risc OS has assigned to the Pi’s GPIO registers – only then can you go ahead and bit bash those locations in assembler.

I knocked up a bit of BASIC code a while back to see how quickly I could toggle a GPIO output on and off and how quickly I could read an input. You may find some of it adaptable to your purposes:

MODE MODE: OFF
ON ERROR ON: REPORT: PRINT" at line "; ERL: END
gpio%=9: REM Set gpio% to the GPIO number we wish to test
SYS “OS_Memory”,13,&20200000,&100 TO ,,,membase%: REM The 41 gpio config registers start at &0×2020000 physical
REM membase% now holds the Risc OS logical start address of the GPIO config registers
PRINTTAB (10,18) "Speed test of R-Pi GPIO “;gpio%;” using Basic assembler read/write loop:"’
PROCassemble
SYS “GPIO_EnableI2C”,0: REM needs Tank’s GPIO module for these two lines
SYS “GPIO_ExpAsGPIO”,2
A%=(1<<gpio%): B%=membase% + &1C
C%=(1<<gpio%): D%=membase% + &28
E%=19700000: t%=TIME
CALL set_unsetGPIO%
s%=TIME – t%
PRINTTAB (10,28) E%;" cycles written in “;s%;” centiseconds",(E%/1000000);“MHz”
SYS “GPIO_ExpAsGPIO”,0
B%=membase% + &34: C%=7700000
t%=TIME
CALL readGPIO%
s%=TIME – t%
PRINTTAB (10,32) C%;" cycles read in “;s%;” centiseconds “,(C%/1000000);”MHz"’’’’’
END

DEF PROCassemble
DIM set_unsetGPIO% 100
P%=set_unsetGPIO%
[OPT 0
SWI “OS_EnterOS”
.more
STR R0,[R1]
STR R2,[R3]
SUBS R4,R4,#1
BPL more
SWI “OS_LeaveOS”
MOV PC,R14
]
DIM readGPIO% 100
P%=readGPIO%
[OPT 0
SWI “OS_EnterOS”
.more
LDR R0,[R1]
STR R0,[R5]
SUBS R2,R2,#1
BPL more
SWI “OS_LeaveOS”
MOV PC,R14
]
ENDPROC