9 Replies Latest reply on Jun 7, 2016 1:15 AM by user_95812785

GPIO output timing

user_95812785 May 16, 2016 10:06 PM

Can anyone help to speed up the GPIO output timing for BCM20737 ?

With the following GPIO function codes below :

// generate SCLK2 High pulse

gpio_setPinOutput(SCLK2_PIN / 16, SCLK2_PIN % 16, GPIO_PIN_OUTPUT_HIGH);

// generate SCLK2 Low pulse

gpio_setPinOutput(SCLK2_PIN / 16, SCLK2_PIN % 16, GPIO_PIN_OUTPUT_LOW);

Measure the SCLK2 high time, and it's about 2.5us. To control one external driver, the SCLK2 high time needs to be around 0.5us.

Is this possible for BCM20737 (I suppose the internal CPU clock should be fast enough) ? or any suggestion ?

1. Re: GPIO output timing

BoonT_56 May 17, 2016 12:02 AM (in response to user_95812785)

Is the below thread helpful to you?

Looking for suggestion for 100hz Pulse generating to GPIO on BCM20732S?
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2. Re: GPIO output timing

user_95812785 May 17, 2016 1:20 AM (in response to BoonT_56)

Thanks, but that doesn't help. What I ask is to shorten but not increase the delay. In my case, the pulse rate is about 500K~1MHz.
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3. Re: GPIO output timing

BoonT_56 May 17, 2016 10:51 PM (in response to user_95812785)

May I know what is the external component that you are driving? And where did you get the above piece of code?
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4. Re: GPIO output timing

user_95812785 May 18, 2016 2:20 AM (in response to BoonT_56)

It's a kind of LED driver with serial data/clock inputs. The piece of code we use (with gpio_setPinOutput and bleapputils_delayUs) is pretty similar to the thread as you said. Its was working for the old model with slower driver, but not for this new one.
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5. Re: GPIO output timing

JacobT_81 May 18, 2016 3:39 PM (in response to user_95812785)

This code will bring out a 2MHz (T = .5us) clock line onto pin 32:

#include "aclk.h"

gpio_configurePin(32 /16, 32 % 16, GPIO_KS_OUTPUT_ENABLE, GPIO_PIN_OUTPUT_HIGH);
aclk_configure(2000000, ACLK0, ACLK_FREQ_24_MHZ);

You can toggle it on and off to try to control your peripheral.

Alternatively, you can route this same clock line through the PWM which is specifically meant for these types of applications. Please see the pwm_tones application in the SDK for example code on using the PWM.

Jacob
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6. Re: GPIO output timing

user_95812785 May 18, 2016 7:29 PM (in response to JacobT_81)

My case is to send out serial data bits one time only (during each change). It's not like PWM with continuous waveform generation. I still hope to know how CPU can handle GPIO control in a fast way.
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7. Re: GPIO output timing

JacobT_81 May 18, 2016 8:02 PM (in response to user_95812785)

There's no faster way to toggle a GPIO. No timer callback will give you anything near 500ns. A clock line is the only thing that can achieve down to the nanosecond level.

The SPI hardware will be able to clock out chunks of 8 bits, but not just 1 bit at a time.

Jacob
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8. Re: GPIO output timing

BoonT_56 Jun 6, 2016 1:19 AM (in response to user_95812785)

Is this still an issue?

user_95812785
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9. Re: GPIO output timing

user_95812785 Jun 7, 2016 1:15 AM (in response to BoonT_56)

still an issue, but just take a walk around with different driver.
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