563xx: reading state of ESSI-controlled pin

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563xx: reading state of ESSI-controlled pin

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AndyS
Contributor I
If PC2 is assigned to the ESSI0 peripheral (frame sync/SC2), can its state be read by the DSP core? As part of init, I need to change the the state of SCK and STD on (near) the rising edge of the frame sync, and my attempts to poll PC2 don't seem to work. A 'scope shows the correct signal being produced by the pin.
 
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rocco
Senior Contributor II
Hi, Andy:

I am currently porting code I've written for the 56002 to the 56309. In the 56002, I could not test the frame-sync the pin directly, but was able to see it's state in the SSI's status register. This should be the same in the ESSI (I hope). Here is the first line of my SSI interrupt service routine:
;
; Test which word interrupted by checking the "Receive Frame Sync" flag.
;
RxInt:    jset    #RFS,x:SSISR,rxLeft         ;branch if left channel
;
;

I am a little confused by the statement that you are trying "to change the the state of SCK and STD on (near) the rising edge of the frame sync". If the ESSI is enabled and running, you won't be able to control those pins. If the ESSI is not yet enabled, and you are trying to synchronize the firmware to an incoming frame-sync in order to enable it synchronous to frame sync (which makes sense), then you should be able to read the pin through the port register. That problem may have to do with the order that you are initializing the ESSI registers.

Hope that helps.
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AndyS
Contributor I
>I am a little confused by the statement that you are trying "to change the the state of SCK and STD on (near) the rising edge of the frame sync". If the ESSI is enabled and running, you won't be able to control those pins.
 
for the duration of the init, I've remapped SCK and STD as General Purpose Outputs. This doesn't seem to prevent the ESSI from generating frame sync, so hopefully the converse is true as well. when i'm done with the init, i hope to just map them back to ESSI control.
 
I'm investigating the RFS/TFS approach ...
 
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