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

GTXTHRCFG (USB3_XHCI) Register

GTXTHRCFG (USB3_XHCI) Register Description

Register NameGTXTHRCFG
Relative Address0x000000C108
Absolute Address 0x00FE20C108 (USB3_0_XHCI)
0x00FE30C108 (USB3_1_XHCI)
Width32
TypemixedMixed types. See bit-field details.
Reset Value0x00000000
DescriptionGlobal Tx Threshold Control Register
For more information on
- Using this register, refer to Architecture Details chapter.
- Selecting values for the fields of this register.
Note:
- All the fields in GTXTHRCFG register are valid only in Host mode.
- GTXTHRCFG register is not applicable for Debug Target.
- GTXTHRCFG register is not applicable in USB 2.0-only mode.

GTXTHRCFG (USB3_XHCI) Register Bit-Field Summary

Field NameBitsTypeReset ValueDescription
Reserved31roRead-only0x0Reserved
Reserved30roRead-only0x0Reserved
USBTxPktCntSel29rwNormal read/write0USB Transmit Packet Count Enable
This field enables/disables the USB transmission multi-packet thresholding:
- 0: USB transmission multi-packet thresholding is disabled; the core can only start transmission on the USB after the entire packet has been fetched into the corresponding TXFIFO.
- 1: USB transmission multi-packet thresholding is enabled. The core can only start transmission on the USB after USB Transmit Packet Count amount of packets for the USB transaction (burst) are already in the corresponding TXFIFO. This mode is only valid in the host mode. It is only used for SuperSpeed.
Reserved28roRead-only0x0Reserved
USBTxPktCnt27:24rwNormal read/write0USB Transmit Packet Count
This field specifies the number of packets that must be in the TXFIFO before the core can start transmission for the corresponding USB transaction (burst). This field is only valid when the USB Transmit Packet Count Enable field is set to one. Valid values are from 1 to 15.
Note: This field must be less than or equal to the USB Maximum TX Burst Size field.
USBMaxTxBurstSize23:16rwNormal read/write0USB Maximum TX Burst Size
When USBTxPktCntSel is 1, this field specifies the Maximum Bulk OUT burst the core can execute. When the system bus is slower than the USB, TX FIFO can underrun during a long burst.
You can program a smaller value to this field to limit the TX burst size that the core can execute.
It only applies to SS Bulk, Isochronous, and Interrupt OUT endpoints in the host mode. Valid values are from 1 to 16.
Reserved15roRead-only0x0Reserved_15
Reserved14roRead-only0x0Reserved1(Rsvd/Rs)
Register field must write only 0 by the application. The read value must be treated as X (unknown).
Reserved13:11roRead-only0x0Reserved (Rsvd/Rs)
The register field must write only 0 by the application. The read value must be treated as X (unknown).
Reserved10:0roRead-only0x0Reserved for future use