AM335x: speed of GPO from PRU

qxc

Hi,

from within PRU for some GPO's there are two possibilities to set/unset them:

via access to SETDATAOUT/CLEARDATAOUT registers in global address space
via PRU-internal register r30

I think the second possibility is much faster, means a write operation to would r30 return earlier than a write-operation to SETDATAOUT/CLEARDATAOUT. My question: how much faster is it? What is the time difference between both methods?

Thanks!

over 9 years ago

0 Biser Gatchev-XID over 9 years ago

TI__Guru**** 393215 points

Are you asking about AM335X GPIOs or about PRU GPOs?

0 qxc over 9 years ago in reply to Biser Gatchev-XID

Genius 5820 points

I'm asking about both, which are the same in this example - the same GPOs (in sense of same output pins) can be set from within PRU in the same way like from within AM335x main core - by accessing the DATA-registers. And they can be set via register r30 - where a difference in speed must exist.

0 Biser Gatchev-XID over 9 years ago in reply to qxc

TI__Guru**** 393215 points

If you toggle the GPIO[3:0] banks from the PRU core access time will not be much different than when you access them from the Cortex-A8 MPU.

If you toggle the pr1_pru[1:0]_pru_r30[15:0] GPOs from the PRU core access time can be as fast as two PRU machine cycles (PRU is running at 200MHz).

0 qxc over 9 years ago in reply to Biser Gatchev-XID

Genius 5820 points

That's interesting, I had assumed accessing GPIO[3:0] banks from the PRU via global address space is slower than direct access via pr1_pru[1:0]_pru_r30[15:0]!

Thanks for your feedback!

0 Biser Gatchev-XID over 9 years ago in reply to qxc

TI__Guru**** 393215 points

Yes it is! I think you misunderstood me. GPIO[3:0] cannot be toggled at more that a few MHz (12.5MHz reached here: http://e2e.ti.com/support/arm/sitara_arm/f/791/t/252598.aspx ), while PRU GPO (R30) can reach up to 100MHz.

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AM335x: speed of GPO from PRU