Zynq UltraScale+ Devices Register Reference > Module Summary > USB3_XHCI Module > GTXFIFOPRIHST (USB3_XHCI) Register

GTXFIFOPRIHST (USB3_XHCI) Register

GTXFIFOPRIHST (USB3_XHCI) Register Description

Register NameGTXFIFOPRIHST
Relative Address0x000000C618
Absolute Address 0x00FE20C618 (USB3_0_XHCI)
0x00FE30C618 (USB3_1_XHCI)
Width32
TypemixedMixed types. See bit-field details.
Reset Value0x00000000
DescriptionGlobal Host TX FIFO DMA Priority Register
This register specifies the relative DMA priority level among the Host TXFIFOs (one per USB bus instance) within the associated speed group (SS or HS/FSLS). Each register bit[n] controls the priority (1: high, 0: low) of TXFIFO[n] within a speed group. When multiple TXFIFOs compete for DMA service at a given time (i.e., multiple TXQs contain TX DMA requests and their corresponding TXFIFOs have space available), the TX DMA arbiter grants access on a packet-basis in the following manner:
- 1. Among the FIFOs in the same speed group (SS or HS/FSLS):
a. High-priority TXFIFOs are granted access using round-robin arbitration
b. Low-priority TXFIFOs are granted access using round-robin arbitration only after the high-priority TXFIFOs have no further processing to do (that is, either the TXQs are empty or the corresponding TXFIFOs are full).
- 2. The TX DMA arbiter prioritizes the SS speed group or HS/FSLS speed group according to the ratio programmed in the GDMAHLRATIO register.
For scatter-gather packets, the arbiter grants successive DMA requests to the same FIFO until the entire packet is completed.
This register is present only when the core is configured to operate in the host mode (includes DRD and OTG modes). The register size corresponds to the number of configured USB bus instances; for example, in the default configuration, there are 3 USB bus instances (1 SS, 1 HS, and 1 FSLS).

GTXFIFOPRIHST (USB3_XHCI) Register Bit-Field Summary

Field NameBitsTypeReset ValueDescription
Reserved31:4roRead-only0x0Reserved
gtxfifoprihst 3:0rwNormal read/write0Host TxFIFO priority