Understanding the 'priority' argument in vc_dispmanx_update_

[ntwk]

I am trying to write some code using the Dispmanx API. The lack of documentation has meant that it's been a slow learning process. I have been using the hello_dispmanx example program has been my primary reference.

As I understand it, drawing operations must first start with a call to

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vc_dispmanx_upate_start()

and then end with a call to

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vc_dispmanx_update_submit_sync()

which flushes the changes to the display.

vc_dispmanx_update_start() accepts a single 'priority' argument. In the hello_dispmanx example the 'priority' argument is assigned a value of 10. All of the other examples I have come across pass in a value of 0.

I have the following questions:

• 1. What does the 'priority' argument do?
  2. What are the acceptable values for 'priority'?
  3. Why is 'priority' assigned a value of 10 in the hello_dispmanx example?