Deferred Image Loading - 2022.1 English

Versal ACAP System Software Developers Guide (UG1304)

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2022.1 English

The PLM supports the Copy to Memory and Deferred Image Handoff features. Based on the scenario, you might have to defer loading a certain subsystem image in the PDI after a certain boot milestone, or defer the handing off to a certain subsystem image. This establishes a certain boot order and can be used to decrease boot time.

Copy to Memory

Images with the copy = <DDR address> attribute specified against them in the BIF file are stored at the specified address in DDR and then loaded during boot PDI load. Specifying the copy attribute takes a backup of the image in DDR, while loading the image. Specifying delay_load in BIF for an image skips the loading of the image altogether.

Specifying copy = <DDR address>, delay_load in BIF takes the back up of the image in DDR and skips loading of the image altogether.

Images are loaded by an IPI command 0x10702 that takes the image ID, function ID as an argument. The IPI command loads and executes these images after all other images start their run. You cannot specify delay_load and delay_handoff simultaneously for an image.

However, you can specify copy and delay_handoff simultaneously for an image.

For partial PDIs, the Copy to Memory feature is not supported.

Deferred Image Handoff

You can pass the delay_handoff attribute to the selected image IDs in the BIF file, which is an input to Bootgen. The PLM reads the delay_handoff attribute and defers the handoff of the images till the end of boot PDI load. In other words, the images with the delay_handoff attribute specified, only start running after the images without the delay_handoff and copy = 1 attributes start their run. Deferred Image Handoff is supported for both full PDIs and partial PDIs.