The USB host transmit interval endpoint n 8-bit registers (USBTXINTERVAL[n]), for interrupt transfers, define the polling interval for the currently selected transmit endpoint. For bulk endpoints, this register defines the number of frames after which the endpoint should time out on receiving a stream of NAK responses.
The USBTXINTERVAL[n] registers values define a number of frames, as follows:
Table 22-54 USB Host Transmit Interval Endpoint n
Registers (USBTXINTERVAL[n]) Frame NumbersTransfer Type | Speed | Valid Values (m) | Interpretation |
---|
Interrupt | Low-speed or Full-speed | 0x01-0xFF | The polling interval is m frames. |
Bulk | Full-speed | 0x02-0x10 | The NAK Limit is 2(m-1) frames. A value of 0 or 1 disables the NAK timeout function. |
The USBTXINTERVAL[n] registers are shown in Figure 22-51 and described in Table 22-53.
Figure 22-52 USB Host Transmit
Interval Endpoint n Registers (USBTXINTERVAL[n])
LEGEND: R/W = Read/Write; -n = value after
reset |
Table 22-55 USB Host Transmit Interval
Endpoint n Registers (USBTXINTERVAL[n]) Field DescriptionsBit | Field | Value | Description |
---|
7-0 | TXPOLL / NAKLMT | 0 | TX Polling / NAK Limit The polling interval for interrupt transfers; the NAK limit for bulk transfers. See Table 22-54 for valid entries; other values are reserved. |