GTXTHRCFG 

         Global Tx Threshold Control Register
   Note:
   - GTXTHRCFG register is not applicable for Debug Target.
   - For more information on threshold settings, see the <link:ext>DWC_usb31_databook:rx_tx_threshold,"Rx and Tx Threshold Settings"</link> section in the Databook.
Module Instance Base Address Register Address
i_usb31_0__ahb_slave__11000000__DWC_usb31_block_gbl__SEG_L4_AHB_USB1_0x0_0x100000 0x1100C100 0x1100C108

Size: 32

Offset: 0x8

Access: RW

Important: The value of a reserved bit must be maintained in software. When you modify registers containing reserved bit fields, you must use a read-modify-write operation to preserve state and prevent indeterminate system behavior.
Bit Fields
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16

reserved_31_27

RW 0x0

UsbTxPktCntSel

RW 0x0

UsbTxPktCnt

RW 0x7

UsbMaxTxBurstSize

RW 0x10

15 14 13 12 11 10 9 8 7 6 5 4 3 2 1 0

UsbTxThrNumPktSel_HS_Prd

RW 0x0

UsbTxThrNumPkt_HS_Prd

RW 0x0

reserved_12_11

RW 0x0

UsbTxThrNumPktSel_Prd

RW 0x0

UsbTxThrNumPkt_Prd

RW 0x0

UsbMaxTxBurstSize_Prd

RW 0x0

GTXTHRCFG Fields

Bit Name Description Access Reset
31:27 reserved_31_27 
Reserved
 RW 0x0
26 UsbTxPktCntSel 
USB Async ESS Transmit Packet Threshold Enable - Host/Device Modes
  
  This field enables/disables the USB transmission multi-packet thresholding for Async endpoints:
   - 0: USB transmission multi-packet thresholding is disabled; the controller starts transmission on the USB as soon as one packet has been fetched into the corresponding TXFIFO.
   - 1: USB transmission multi-packet thresholding is enabled. The controller 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 valid in both host and device mode. It is only used for Enhanced SuperSpeed.
  
  In device mode, the controller can send ERDY on the USB after USB Transmit Packet Count amount of packets for the USB transaction (burst) are already in the corresponding TXFIFO of a Bulk IN endpoint
 RW 0x0
25:21 UsbTxPktCnt 
USB Async ESS Transmit Packet Threshold Count - Host/Device Modes
  
  This field specifies the number of packets that must be in the TXFIFO before the controller can start transmission for the corresponding USB transaction (burst) for Async endpoints. This field is only valid when the USB Async ESS Transmit Packet Threshold Enable field is set to one. 
  
   For device mode, this field specifies the number of packets that must be in the TXFIFO before the controller can start transmission of ERDY for the corresponding USB transaction (burst) of Bulk IN endpoint. 
  
  Valid values for this field is 1 to 16.
  
  Note:
   - In host mode, this field must be less than or equal to the USB Maximum TX Burst Size field.
   - In device mode, this field must be less than or equal to the USB endpoint maximum Burst Size amongst all endpoints.
 RW 0x7
20:16 UsbMaxTxBurstSize 
USB Async ESS Maximum TX Burst Size - Host Mode Only
  
  When USBTxPktCntSel is 1, this field specifies the Maximum ESS Bulk OUT burst that the controller can execute. When the system bus is slower than the USB, TXFIFO can underrun during a long burst. 
  
  You can program a smaller value to this field to limit the TX burst size that the controller can execute. 
  
  It only applies to ESS Bulk OUT endpoints in the host mode. Valid values are from 1 to 16. 
  
  Note: This field can only be set to 2, 4, 8 or 16.
 RW 0x10
15 UsbTxThrNumPktSel_HS_Prd 
USB HS High Bandwidth Periodic Transmit Packet Threshold Enable - Host Mode Only
  
   This field enables/disables the USB HS High Bandwidth Periodic transmission multi-packet thresholding>
   - 0: USB HS High Bandwidth Periodic transmission multi-packet thresholding is disabled; the controller can start transmission on the USB as soon as one packet has been fetched into the corresponding TXFIFO.
   - 1: USB HS High Bandwidth Periodic transmission multi-packet thresholding is enabled. The controller can start transmission on the USB only after USB HS High Bandwidth Periodic Transmit Packet Threshold Count number of packets for the Periodic High Bandwidth USB transaction is already in the corresponding TXFIFO. This mode is valid in host mode for high speed high bandwidth periodic endpoints.
  
  Note: The intent of using this bit is only when the system bus is slow and not able to cater to the data rate of High-Bandwidth endpoint (3076 bytes/uframe). If the system bus is slow, and if all the transactions of a High-Bandwidth endpoint could not be executed successfully, it would likely cause a compliance test failure (section 5.4.x of xHCI Compliance Test Specification). This issue is seen only with older PCI based USB-IF compliance devices.
 RW 0x0
14:13 UsbTxThrNumPkt_HS_Prd 
USB HS High Bandwidth Periodic Transmit Packet Threshold Count - Host Mode Only
  
   This field specifies the number of packets that must be available in the TXFIFO before the controller can start transmission for the Periodic High Bandwidth USB transaction. This field is only valid when the USB HS High Bandwidth Periodic Transmit Packet Threshold Enable field is set to one. Valid values are from 1 to 3.
 RW 0x0
12:11 reserved_12_11 
Reserved
 RW 0x0
10 UsbTxThrNumPktSel_Prd 
USB Periodic ESS Transmit Packet Threshold Enable - Host Mode Only
  
  This field enables/disables the USB Periodic transmission multi-packet thresholding:
   - 0: USB transmission multi-packet thresholding is disabled; the controller starts transmission on the USB as soon as one packet has been fetched into the corresponding TXFIFO.
   - 1: USB transmission multi-packet thresholding is enabled. The controller can start transmission on the USB only after USB Periodic ESS Transmit Packet Threshold Count amount of packets for the USB transaction (burst) has been fetched into the corresponding TXFIFO. It is used only for ESS.
 RW 0x0
9:5 UsbTxThrNumPkt_Prd 
USB Periodic ESS Transmit Packet Threshold Count - Host Mode Only
  
  This field specifies the number of packets that must be in the TXFIFO before the controller can start transmission for the corresponding USB transaction (burst). This field is valid only when the USB Periodic ESS Transmit Packet Threshold Enable field (UsbTxThrNumPktSel_Prd) is set to one. Valid values are from 1 to 16.
  
  Note: This field must be less than or equal to the USB Maximum Periodic TX Burst Size field.
 RW 0x0
4:0 UsbMaxTxBurstSize_Prd 
USB Maximum Periodic ESS TX Burst Size - Host Mode Only
  
  When UsbTxThrNumPktSel_Prd is 1, this field specifies the Maximum Periodic OUT burst the controller can execute. When the system bus is slower than the USB, TXFIFO can underrun during a long burst.
  
  Note: This field can only be set to 2, 4, 8 or 16.
 RW 0x0