Re: [beagleboard] Changing pin mode by writing in Pinmux register

[Charles Steinkuehler]

On 7/13/2015 10:11 AM, Babak akbari wrote:
 Hello
 
 In AM335x (TRM) I have read that every pin has 8 different modes,each pin 
 has specific register like (conf_gpmc_ad0) that you can change the pin mux 
 mode from [0:7] . There are specific offsets for the pins from the base 
 address ((0x44E1_) region name (Control Module))
 I am able to read these registers correctly but my problem is in changing 
 the value of these registers.

The pinmux registers are protected by the Linux kernel and cannot be
written to by normal user code.  You either need to properly configure
the registers using device-tree bindings or circumvent the
restrictions (ie: by doing something like directly writing the pinmux
register with the PRU, which has direct hardware access and doesn't go
through the ARM side page map tables).

Note there is a bone-pinmux-helper driver which was written to allow
easy user-mode changing of the pinmux registers via sysfs.  See the
universal overlay (and the accompanying config-pin script) for an
example of usage:

https://github.com/cdsteinkuehler/beaglebone-universal-io

-- 
Charles Steinkuehler
char...@steinkuehler.net

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[beagleboard] Changing pin mode by writing in Pinmux register

[Babak akbari]

Hello

In AM335x (TRM) I have read that every pin has 8 different modes,each pin 
has specific register like (conf_gpmc_ad0) that you can change the pin mux 
mode from [0:7] . There are specific offsets for the pins from the base 
address ((0x44E1_) region name (Control Module))
I am able to read these registers correctly but my problem is in changing 
the value of these registers.
I used   (chmod 777 pinmode) to change the permissions. but the problem 
of writing is still remain
The following is the C code I have used.

#define CONTROLMODST 0x44E1
#define CONTROLMODED 0x44E11FFF
#define CONTROLMODSIZE (CONTROLMODED - CONTROLMODST)
#define PINREGOFF 0x808
#define SYSBOOT 0x40
#define REV 0x00

#define MODE0 0x0
#define MODE1 0x1
#define MODE2 0x2
#define MODE3 0x3
#define MODE4 0x4
#define MODE5 0x5
#define MODE6 0x6
#define MODE7 0x7

#include stdio.h
#include stdlib.h
#include sys/mman.h
#include sys/stat.h
#include fcntl.h
#include unistd.h


int main(int argc, char *argv[]) {
volatile void *start_addr = NULL;
volatile unsigned int *pinreg =NULL;
volatile unsigned int *sysboot =NULL;
volatile unsigned int *rev =NULL;
unsigned int reg;

int fd = open(/dev/mem, O_RDWR);

 printf(Mapping %X - %X (size: %X)\n, CONTROLMODST, CONTROLMODED, 
CONTROLMODSIZE );
 start_addr = mmap(0, CONTROLMODSIZE, PROT_READ | PROT_WRITE,MAP_SHARED, 
fd, CONTROLMODST);

 pinreg=start_addr+PINREGOFF;
 sysboot=start_addr+SYSBOOT;
 rev=start_addr+REV;
  if(start_addr  == MAP_FAILED) {
printf(Unable to map\n);
exit(1);
}

  printf(Mux mapped to %p\n, start_addr);
  printf(Pinreg mapped to %p\n, pinreg);
//  printf(Sysboot mapped to %p\n, sysboot);
//  printf(Rev mapped to %p\n, rev);
  reg=*pinreg;
  printf(reg before changing %p\n, reg);
  reg=reg|(reg+(11));

  *pinreg=reg;
//  printf(reg after changing %p\n, pinreg);
  printf(reg after changing %p\n, *pinreg);
//  reg=*sysboot;
//  printf(reg before changing %p\n, reg);
//  reg=*rev;
//  printf(reg before changing %p\n, reg);
}



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