GPIO Speed

Hello All,

I have created a sample driver {derived from leds and pwm} to test gpio and
a sample program to test the pin number, both are working perfect, Now in
simple c program If i run make pin high and low continuous in while loop,
in oscilloscope i get 382 khz freq. while people saying they can get
800-900khz of freq. 


People say use pwm, yes i am using pwm pin 24 of con4, but no luck. If i
disable the pwm then also i get the same freq. 

can someone please tell me how can i get more frequency, is there any
patch, certain modification in kernel? 

Please let me know.

Thank You for your time and consideration.

Hello miniarm,
Do you use OS or not, i'm using WinCE and using GPIO driver.
I'm doing the same thing in C# and i can get a frequency arout 50MHz or
more. By using the PWM, i can create 12.5MHz frequency

Hello Judau,

Yes, I am using Linux image and GPIO driver, in c program I am constantly
making pin high and low and measure speed in osicoloscope, I only get 382
khz, if i use the pwm then also no difference in freq. 

can you please guide on this?

Thanks & Regards,
miniarm

I'm so sorry,I'm using WinCE so i can't help you very much!
did you read the arm920T datasheet? You can get more infos about hardware
(registers, I/O...)then you'll know how to do.

Good luck. 
Judau

Judau,

Could you briefly explain the process for getting such high GPIO speeds
with an intervening OS?.  I have no WinCE experience, but based on my
limited Linux experience that seems several orders of magnitude faster than
I would have guessed.

Thanks,
Dave

A user space GPIO driver is going to be very slow if it relies on being
serviced by the OS for each change. I don't recall what a jiffie is on this
Linux, but typical is maybe 4ms or 250 per second.

I'm working on (and seeking help with) a set of drivers that use DMA and
can be configured to take or send data in bursts at various speeds right up
to the memory bandwidth of 100MHz or better for digital I/O and SPI at max
rate for chips like fast A/D converters.

My own app is underwater acoustics with chirps from 150 to 250 KHz and they
need to be oversampled. 2MHz quadrature sampling from two channels would be
great and with data bursts of one or two seconds. I would collect about 4
MBytes of data every second. On the Mini2440 it needs to be logged to SD or
networked to a bigger data collection point. On the 6410, there may be
enough speed with the VPU to do real-time pulse compression with FFTs and
greatly reduce the data. On the Mini210, I think the whole thing can be
done on board and resulting synthetic aperture sonar images displayed as
the boat moves. Perhaps Mini6410's --> Mini210. I'll start a topic on DMA
drivers.

Dear Charles,

using driver i configure gpio and from simple c code i am sending data on
that pin and measure freq. on oscilloscope. can you please show me the path
where i should heading, kernel code changes etc..

I want to drive a servo motor connected with gpio, if i get more speed,
that will be much great.

in driver GPB0 pin i am using as a pwm.

I can come on skype if you're on skype too.

Thank you for your time and consideration.

--miniarm

With the drivers available now, I think the best way is to use something
like an Arduino for your real-time servo control with distance, speed, etc.
set by the Mini2440 over serial or I2C or ?

-- Charlie

Hi Charles,

Thank you for pointing me out there at Ardunio, but i want to use mini2440
board with gpio pin available on the board and wants to achieve output.
driver works well and program is also complete, but it will be great if i
can achieve little more frequency than 382 khz. 

please guide me on this, meanwhile i am trying to compile linux 2.6.39,
look forward to hear from you soon.

Regards,
miniarm

does this problem solve if i use rt kernel?

plz help !

Miniarm,

what does:

> People say use pwm, yes i am using pwm pin 24 of con4, but no luck.

exactly mean? What did you try? Pin 24 at CON4 is GPG11 at the CPU. This
pin can act as GPIO, external interrupt or clock input for timer 1.
But not as PWM output. Use GPB0, GPB1, GPB2 or GPB3 instead. They can act
as PWM outputs.

Juergen,

my mistake, I use pin 31 of con4 that is GPB0 as pwm output. pwm output
comes as per the application need, but i am not getting freq. above 382
khz, it will be great if somehow i can get max freq. arround 800-900 khz.

with rt kernel no luck instead cpu responding very slow, i am now trying to
get 3.1 kernel in board.

please let me know if you have other solution in mind, or perhaps there
must be other way which i don't know. please suggest me a correct way.

regards,
miniarm

miniarm what are you trying to do with the frequency? servo control?

Yes, trying to control servo motor connected with con4 using gpio.

I will post that video next week

I mean the video tutorial of how to do that.

Andre,

If you know any kernel changes, perhaps need to apply patch or something
else, then please let me know.

my solution is working fine, but all i want to achieve more freq. as per
Jaydeep said above and i am using driver and userspace c program to test
the freq.

--
miniarm

Miniarm: How did you program the timer to generate the PWM output signal?

@Juergen,

using pwm logic.

I mean: How did you program the timer register to setup the PWM timing and
pulse width?

@Juergen,

I installed 2.6.39 kernel without rt patch, system is running fine, but
still not able to get a good freq. 

can you please help me out there?

--
miniram

@dave, @juergen,

Any solution for this problem? also i am facing problem with dm900 ethernet
driver, i am getting very low speed with new kernel also got some error of
'wrong data' when ping from outside.

--miniarm

Hello miniarm,

How's about the pin frequency? Do you success?

@judau,

No, Still not get success, also tried rt patched kernel, but no luck. Can
you please help me out in this situation? or show me some path, perhaps..!

regards,
miniarm

miniarm, did you read the S3C2440 processor's user manual, chapter 10, how
the PWM works in your CPU? The base clock of these PWM timers is the
internal "PCLK" which runs mostly at 66 MHz. There are some dividers to
scale down this frequency, but at the end, this frequency is used to
generate your PWM output signal. And with a base frequency of 66 MHz you
should reach your frequency requirements.

@Juergen,

I've already known about that, but i want to shift data with high speed
(around 20MHz) via port to another device! Can you help me?

Thanks in advance!

@miniarm
If you can disable all threads and interrupts, it will be faster (the
application runs on OS).

@Juergen,

Thanks for the reply, but I've tried changing parameter of pwm in driver as
per the mentioned in the sheet. Tried changes prescaler to 1/2 but no lucj,
If i try non pwm pin let's say pin 9 of CON4, still I am getting only 382
KHz freq, and If i increase CONFIG_HZ value, my touch screen stop
responding.

@Judau,
How can i disable all threads and interrupts? please advice. If i do cat
/proc/interrupts it list only releiving intetturpt only like touch screen,
timer, ethernet, watchdot, etc. Here is the output
30:    1485552         s3c  S3C2410 Timer Tick
 32:          0         s3c  s3c2410-lcd
 37:          0         s3c  s3c-mci
 42:          0         s3c  ohci_hcd:usb1
 43:          0         s3c  s3c2440-i2c
 51:      57812     s3c-ext  eth0
 60:          0     s3c-ext  s3c-mci
 70:        221   s3c-uart0  s3c2440-uart
 71:       1270   s3c-uart0  s3c2440-uart
 79:          0     s3c-adc  s3c2410_action
 80:          0     s3c-adc  adc, s3c2410_action
 83:          0           -  s3c2410-wdt


Can you please tell me which one should i disable in order to get max. freq
at the same time touch screen should works well.

thank you for your time in advance.

regards,
miniram

I think you'll have to mmap() the GPIO registers and write them from the
userspace app.

Performing a kernel call (even if it does nothing) uses up about 60
sequential CPU cycles, so if the CPU freq is ~450Mhz, you'll be able to
call the kernel with at most ~7.5Mhz. If the call actually does something,
this number will be reduced further.

The bottleneck here is not the PCLK, but the FCLK and the kernel call
itself.

@Ceiliedgh

Can you tell me how to mmap() the GPIO reg. in C#?
I'm using WINCE.
Thanks

AFAIK there is no support for mapping arbitrary memory addresses in C# (at
least the .NET 3.5 framework doesn't support it and it is unlikely to be
supported in the future).

Maybe you could work around it by using an unmanaged library to do the GPIO
business, though it looks like that the Win32 API only supports memory
mapping of files, not arbitrary memory addresses :(

I've made a software in C that runs at 2MHz. Funny thing is that not all
pins runs on same speed. GPM runs at 380Khz while GPQ runs at 2MHz. If you
use both, system sets all at lower speed.

Forgot about using sysfs GPIO implementation. Use mmap on /dev/me instead.

Friends I found the driver for servo on
http://www.mahumi.limanowa.pl/video/9y6kIe9jpu8/mini2440-servo-control-f...,

i want to toggle on/off from 2 pin of port to more. If you have The gpio
driver, please tell me about how to custome on gpio driver!

Thanks in advance!

Here is how to toggle on/off but if you are running other application it
would slow down the toggle

http://www.youtube.com/watch?v=CpjgujlyQJQ