Hi Charles, Thank you very much for your answer. I manage to access it after enable ADC using 'echo BB-ADC > /sys/devices/bone.capemgr.*/slots' . Though I could only do it in kernel 3.8, later kernel (3.12) gives an error saying symbol ocp could not be found. I do not really know how to change the .dts to get it working . Anyhow, I will work with 3.8 for now.
Sincere, Nhan Nguyen On Wednesday, February 19, 2014 2:57:31 PM UTC+1, Charles Steinkuehler wrote: > > On 2/19/2014 7:43 AM, Nhan Nguyen wrote: > > Hi everyone, > > > > I have been trying to use PRU to read multiple ADC inputs. Unfornately, > I > > am stuck at accessing to the ADC registers (chapter 12 on AM335x > technical > > reference manual). I set the OCP registers, checked the PMAO registers > on > > PRU to ensure access to external host. For example, I read the ADC > REVISION > > as below: (tried to write to STEPCONFIG and STEPENABLE, etc.) > > > > MOV r13, 0x44E0D000 //ADC REVISION > > LBBO r5, r13, 0, 4 > > SBCO r5, C28, 4, 4 //store REVISION to shared memory to show with C > > program > > > > .. but everything returns 0. > > > > I install Ubuntu 13.04 on Beaglebone Black, tried kernels 3.8, 3.12. PRU > > worked with shared memory accessing, and GPIO1 registers (I am not sure > > what to try next) . I haven't tried it on the official Angstrom image, > > because I still couldn't get PRU to work right away on it. > > I suggest you remove the PRU from the setup temporarily and try directly > reading the memory from C. This will be a lot easier to debug, and the > PRU has no chance of reading ADC values if you can't read them from the > ARM. > > As a guess, I suspect you don't have the ADC hardware setup properly and > are getting bus faults when reading. This will show up as an error if > you try to read the memory location from the ARM (making it easier to > debug). Make sure you have loaded a device tree overlay that enables > the TSC hardware (Touch Screen Controller = ADC) and populates an > appropriate state-machine instruction table to digitize the values you > are interested in. Unlike simpler microcontrollers, each major > subsystem in the AM335x can be powered up or shut down, and by default > most systems (ADC, PWM, etc) are powered down with their clocks disabled > until you explicitly enable them. > > Once you can properly read the values from a raw memory location using > the ARM, the PRU should be able to read them as well. > > -- > Charles Steinkuehler > [email protected] <javascript:> > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
