AM3358 : GPIO read latency

gyosun sim

Part Number: AM3358

Hello,

I'm using the AM3358 CPU to control my GPIO.

To improve speed, the driver has the following control:

pGPIO3 = (volatile unsigned char *)ioremap(0x481AE000, 0x1000);
pGPIO3_DIR = (volatile unsigned int *)(pGPIO3 + 0x134);
pGPIO3_IN = (volatile unsigned int *)(pGPIO3 + 0x138);
pGPIO3_OUT = (volatile unsigned int *)(pGPIO3 + 0x13C);

//write

*pGPIO3_OUT = val;

//read

val = *pGPIO3_IN;

However, GPIO Read time is much longer than write as shown below.

Is there any way to control faster without using a PRU?

Thank you.

Best regards.

gyosun.

over 6 years ago

0 Biser Gatchev-XID over 6 years ago

TI__Guru**** 393215 points

Hi,

What software is this? Linux or RTOS? Which version?

0 gyosun sim over 6 years ago in reply to Biser Gatchev-XID

Intellectual 745 points

Hi Biser,

I wrote a device driver under Linux to control GPIO.

Thank you,

Best Regards,

Gyosun.

0 gyosun sim over 6 years ago in reply to gyosun sim

Intellectual 745 points

hi,

I looked for more data.

http://www.ti.com/lit/an/sprace8a/sprace8a.pdf

Imported part of the link's material.

I'm using GPIO3, and according to the data, 34 cycles is delayed.

34cycle = 170ns @ 200MHz

In the above question, is the delay of about 230ns for reading logically correct when including the software delay?

I hope someone will give me the correct answer.

Thank you,

Best Regards,

Gyosun.

0 RonB over 6 years ago in reply to gyosun sim

TI__Mastermind 30856 points

Hello,

Using the PRU will be the absolute best case for reading a GPIO. Linux will always incur additional software scheduling delay which will vary depending on system load. I think what you are seeing so far is likely absolute best case. If you ran the system for days with varying loads, I would expect it to vary considerably. If you need RT performance (i.e. low, deterministic delay on reading the GPIO), the PRU is the best way.

I hope this is helpful to you.

0 gyosun sim over 6 years ago in reply to RonB

Intellectual 745 points

Hi RonB,

It was recognized that the best speed was achieved without using a PRU.

Thank you for answer.

Best Regards,

Gyosun.

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AM3358 : GPIO read latency