AM335x - Problem Configuring eCAP module to Generate PWM

James Evans

Hello!

We are trying to configure the eCAP module to generate a PWM output signal on ECAP0_IN_PWM0_OUT.

When the ECCLT2_REG value is read, the CPU halts.

Any ideas why simply reading this register causes the CPU to halt? Does this mean a peripheral isn't correctly enabled or a clock that isn't turned on?

Here is the code run from u-boot:

Is there anything missing from this code, such as missing configuration steps?

Additionally, here is the current mux configuration, which is also done in u-boot:

Is this the correct way to mux the pins for the eCAP module?

Any feedback here would be most helpful.

Thanks,

James

over 10 years ago

0 Biser Gatchev-XID over 10 years ago

TI__Guru**** 393215 points

Hi James,

Probably you are trying to read this register too fast. Try reading the PWMSS CLKSTATUS register first to see if the clock to eCAP is already enabled.

0 Joshua Parrish1 over 10 years ago in reply to Biser Gatchev-XID

Prodigy 210 points

Hi Biser,

James posted this question for one of my clients. I have passed on your answer, thank you.

That said, my understanding is that the eCAP module is not producing a PWM. Can you please comment on the muxing within Uboot? I fear that the problem resides within those steps. The client plans to use the eCAP through a bare-metal application ran after Uboot. The muxing has been compiled into Uboot.

0 Biser Gatchev-XID over 10 years ago in reply to Joshua Parrish1

TI__Guru**** 393215 points

Pin mode is 0, which is correct. The other thing is that they have internal pulldown enabled. I don't know what they have connected to this pin externally, but maybe they should try disabling the pulldown (register value 0x08).

0 Joshua Parrish1 over 10 years ago in reply to Biser Gatchev-XID

Prodigy 210 points

Hi Biser, et al. ,

From my client, "

I tried both of these changes a) waiting for the eCAP clock to be enabled and b) setting the pin mux to 0x08 without any luck.

0 Biser Gatchev-XID over 10 years ago in reply to Joshua Parrish1

TI__Guru**** 393215 points

The other thing I can suggest is to check how the Linux PWM driver initialises eCAP and use the same process flow. ()http://processors.wiki.ti.com/index.php/Linux_Core_PWM_User%27s_Guide)

0 James Evans over 10 years ago in reply to Biser Gatchev-XID

TI__Mastermind 49692 points

Hi Josh,

I took a look at the Linux PWM User's Guide provided by Biser.

After building the eCAP module in the kernel, the eCAP can be controlled from the Linux user space through SYSFS interface.

If the eCAP works correctly this way, perhaps a shell script can be created to initialize the eCAP at startup, instead of doing this in u-boot.

The script can be added to the /etc/init.d directory (e2e.ti.com/.../327947).

Hope this helps.

James

0 melissaw over 10 years ago in reply to James Evans

TI__Genius 15900 points

Hi Joshua,

One important item to note about the eCAP is that most of its registers (including ECCTL2) are 16-bit wide only. You’ll want to make sure that you access only that size.

The AM335x Starter Kit diagnostic code uses the eCAP in APWM mode (here). This code is based on StarterWare (not Linux), but it still may be a useful example. Note that the eCAP driver in the StarterWare package uses the function HWREGH (instead of HWREG) when accessing the ECCTL2 register, where HWREGH is defined as:

#define HWREGH(x) (*((volatile unsigned short *)(x)))

Regards,

Melissa

0 Joshua Parrish1 over 10 years ago in reply to melissaw

Prodigy 210 points

Hi Melissa, The issue ended up being the 16-bit wide address. Thank you.

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AM335x - Problem Configuring eCAP module to Generate PWM