GPIO input and output response time problem

Keldy

Hi,

I'm using Am335x with PSP04.06.00.07, I'm using GPIO1_24 as input, and GPIO1_20 as output. i have write a GPIO kernel driver, using the ioremap() function to map the GPIO1 module.

initially, the GPIO1_20 (output) will output logic 1, when GPIO1_24 (input) detecting level logic 1, i need GPIO1_20 (output) to output logic 0. From scope, the result as following:

200ns (pulse)

__ logic 1

| |

GPIO1_24(input)___________| |____________________________________ logic 0

400ns

|----------|

GPIO1_20(output)__________________ logic 1

|_________________________________logic 0

From the scope, i see my my kernel driver can detect the GPIO1_24 input signal pulse with 200ns, but my GPIO1_20 will only pull low after 400ns.

my code for doing this task is as following:

while(!(*gpio1_24 & (1 << 24))); //waiting GPIO1_24 input logic 1

*gpio1_20 |= (1 << 20); //output GPIO1_20 logic 0

Why and What cause this delay problem to GPIO?

Is it because the CPU take time to serving each module across the interconnection L3 and L4 cross bar? causing a wait state to service GPIO module ?

I want my GPIO1_20 pull to low after detect logic 1 from GPIO1_24 in 100ns.

i have already try using the rising edge interrupt on GPIO1_24 (input), result is even more worst than polling method, It is because interrupt process in kernel not same as the low level programming interrupt process?

Thanks and Regards,

Keldy

over 13 years ago

0 Renjith Thomas over 13 years ago

Guru 31670 points

Keldy,

Try writing the same code assembly, might help. There will be a couple of instructions running between the C two statements. Have a closer look at the disassembly, you might be able to write a better optimized assembly code.

Also, you can check the L3/L4 configs, bus priority etc. I'm not sure about the bus architecture in case of AM335x.

0 Darrin Hansen over 13 years ago

Intellectual 810 points

Here is another recent post related to what you are attempting:

http://e2e.ti.com/support/dsp/sitara_arm174_microprocessors/f/791/t/202814.aspx

Darrin

0 Keldy over 13 years ago in reply to Darrin Hansen

Expert 1835 points

Hi,

i write my code using Gedit, not the code composer IDE, and my code is a code for kernel space used. i'm using arm-arago-linux-gcc compiler, how i disassemble my C code ?

i have already change the priority of the interconnection, no any improvement from the action. GPIO1 module is under L4_PER slave, and L4_PER is under TPTC master, i have configure the TPTC(0 - 2) read and write to priority 3 in control module register.

Thanks and Regards

Keldy

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GPIO input and output response time problem