Why I can't modify AM335X Pad Control Registers

Peng Liu50174

Other Parts Discussed in Thread: SYSCONFIG

Hi,

I have a AM335EVM.On this board, the GPIO0_7 is configured as one GPIO port to turn on/off LCD backlight,i.e.MUXMODE=0x7

In order to do some experiment about the eCAP0/APWM in the PRU firmware, the MUXMODE should be changed to 0x3. However I found the MUXMODE can't be changed--I wrote 0x3, but still 0x7 when read back.

I checked other registers,CM_WKUP_CONTROL_CLKCTRL is enabled and not idled(0x00000002), and CONTROL_SYSCONFIG is smart idle/standy(0x00000002A). So I think MUXMODE in the pad control registers can be modified. But the result is not. Please help what others registers need to set.

Thanks,

over 14 years ago

0 Vaibhav Bedia over 14 years ago

TI__Expert 5290 points

Hi,

How are you trying to change the pin-muxing? Userspace utilities like devmem can't write to the pin-mux registers. Have a look at http://processors.wiki.ti.com/index.php/AM335x_PSP_User%27s_Guide#Modifying_Pin_Mux_settings

Regards,

Vaibhav

0 Gururaja Hebbar over 14 years ago

TI__Intellectual 2725 points

can you tel me how you changed the mux mode.

0 Peng Liu50174 over 14 years ago in reply to Gururaja Hebbar

Expert 1510 points

The firmware simply uses following assemble codes to change the pin mux setting for GPIO0_7

#define conf_ecap0_in_pwm0_out_reg (0x44E10000+0x964)
    LDI r12.w0, conf_ecap0_in_pwm0_out_reg & 0xFFFF
    LDI r12.w2, conf_ecap0_in_pwm0_out_reg >> 16
    MOV32 r13,3
    SBBO r13, r12,0x0,4    //set conf_ecap0_in_pwm0_out

0 Anil over 14 years ago in reply to Peng Liu50174

TI__Expert 6655 points

Hi Peng Liu,

Your settings are getting overwrite by some other portion of code. Check the details on where its getting modified?

Regards

AnilKumar

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0 Peng Liu50174 over 14 years ago in reply to Anil

Expert 1510 points

Hi,

I was suspecting that the setting was owerwritten by other threads. But I did read out the registers right after setting it, still got 0x7．

LBBO r13, r12,0x0,4
SBBO r13,global.dst,4,4 //read out the mux setting to global.dst

I also tried to configure other PIN mux setting, still found the registers value counldn't be modified. Perhaps PRU firmware can't change the PIN-MUX setting. Only the code of ARM can change PIN-MUX.

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Why I can't modify AM335X Pad Control Registers