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AM3358 Using DMTimer pins to measure input pulse width

Robert Stewart
Prodigy 50 points

I'm trying to use the timer pins (gpio2[2...5]) to measure pulse with on a Beaglebone with the 25 MHz clock. The pin mux mode is correctly set to 2 and pull up/down are disabled and capture mode is set on the timers. When I connect a push button attached to 3.3v to one of the four timer pins I correctly get capture interreupts on low to high and high to low transitions and I can measure the timer difference between them without issue. 

However, if I set up a signal generator for 50 Hz 3.3v square wave and attach it to a timer pin, I get no interrupts at all. Looking on a 'scope at the timer pin, the pulse train amplitude has drop from 3.3 volts to about 1.0v. Does anyone have any ideas on what would cause such a drop in amplitude? Also, if simply toggle the mux mode between timer and gpio (that is between mode 2 and 7) the amplitude of the pulse train is either 3.3v or 1.0v. I can get gpio interrupts on the pulse edges if I set the mode to to 7 but never get capture interrupts with the same input when in mode 2.

Thanks for any suggestions.

Bob Stewart

  • 0
    TI__Guru**** 393215 points

    Hi Bob,

    Can you post your pinmux settings?

  • 0 in reply to Biser Gatchev-XID
    Prodigy 50 points

    Thanks for the reply Biser.

    I'm not running Linux but here are the register settings related to the control modules pin muxing after they have been set:

    [init -> ctl_module_drv] Pin mux setting is B=2, P=2, Mode=2, Input=1, Offset=36, Pullup is 0
    [init -> ctl_module_drv] Pin mux setting is B=2, P=3, Mode=2, Input=1, Offset=37, Pullup is 0
    [init -> ctl_module_drv] Pin mux setting is B=2, P=4, Mode=2, Input=1, Offset=38, Pullup is 0
    [init -> ctl_module_drv] Pin mux setting is B=2, P=5, Mode=2, Input=1, Offset=39, Pullup is 0

    The B is for GPIO Bank and the P is the pin number within the bank so this is showing the settings for pins 66 through 69 which correspond to Timers 4 through 7.

    Since I can get the capture interrupt on a timer when I use a button attached to 3.3v that would indicate that the pin mux settings are correct, I believe.

    Thanks,

          Bob

  • 0 in reply to Robert Stewart
    TI__Guru**** 393215 points

    Robert Stewart said:
    [init -> ctl_module_drv] Pin mux setting is B=2, P=2, Mode=2, Input=1, Offset=36, Pullup is 0
    [init -> ctl_module_drv] Pin mux setting is B=2, P=3, Mode=2, Input=1, Offset=37, Pullup is 0
    [init -> ctl_module_drv] Pin mux setting is B=2, P=4, Mode=2, Input=1, Offset=38, Pullup is 0
    [init -> ctl_module_drv] Pin mux setting is B=2, P=5, Mode=2, Input=1, Offset=39, Pullup is 0

    Unfortunately this means nothing to me. I suppose you have GND connected between the two boards.