Linux/AM5726: fastest way to share data with DSP

Colombo Carlo

Mastermind 24280 points

Part Number: AM5726

Tool/software: Linux

Hello everybody ,

I m using Linux on A15 . I would like to offload A15 , having some tasks moved in the DSP

being motor control I need a fast communication between the A15 and DSP .

as for now using rpmsg I got 70us just to exchange one message : I need to be much better ( ideally < 10uS )

how can I proceed ? where to find info on doing this ?

could LInuxRT give me better results ?

best regards

Carlo

over 6 years ago

0 Rex Chang over 6 years ago

TI__Guru 50170 points

Hi, Carlo,

LinuxRT won't help. The priority of the processes are not high enough to take advantage. You may want to come up with different approach by not using IPC/RPMSG, but exposing mailbox to user space API combined with a shared memory space between ARM and DSP.

We see some use cases in the field and recently submitted a feature request for a low latency high throughput IPC internally. If it gets the resources, it will be revamped.

Rex

0 Colombo Carlo over 6 years ago in reply to Rex Chang

TI__Mastermind 24280 points

Hi Rex ,
please do you have an example on mailbox and shared ram setup ? it will be great help
any doc I can have a look ?
thank you
best regards
Carlo

0 Rex Chang over 6 years ago in reply to Colombo Carlo

TI__Guru 50170 points

Carlo,

Mailbox is not exposed to user space so we don't have example. Shared memory is basically linux and dsp configuration. Linux defines a reserved physical area which DSP maps its local memory to that physical area. You can take a look at the Big Data IPC example on the shared memory setup,

software-dl.ti.com/.../index_examples_demos.html

Rex

0 Colombo Carlo over 6 years ago in reply to Rex Chang

TI__Mastermind 24280 points

Hi Rex ,
thank you I ll study in more details
please any idea on which latency ( time a data from one side is on the other ) I can expect ?
best regards
Carlo

0 Rex Chang over 6 years ago in reply to Colombo Carlo

TI__Guru 50170 points

Hi, Carlo,

We started benchmarking IPC recently. On AM57x, we see average round trip time of 120-130us. This is just average. We've seen 0.1% go more than 500us. We haven't been able to explain it though.

Rex

0 Colombo Carlo over 6 years ago in reply to Rex Chang

TI__Mastermind 24280 points

HI Rex ,
great ! I ll keep you posted
best regards
Carlo

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Linux/AM5726: fastest way to share data with DSP