Initial Commands to USB Controller

Zynq UltraScale+ Device Technical Reference Manual (UG1085)

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2.4 English

There is only one command ring that is used for issuing xHCI specific commands or commands related to device slots.

The command ring control register is defined in the operational register space. All xHCI commands are issued by placing the desired command TRB(s) on the command ring, then ringing the xHCI command doorbell register, that is writing the host controller command code to the DB target field of doorbell register 0.

All commands result in the generation of a command completion event TRB on the event ring.