Universal Serial Bus Controller User's Guide

4.68 NAKLimit0 Register (Host mode only) (HOST_NAKLIMIT0)
4.69 Transmit Interval Register (Host mode only) (HOST_TXINTERVAL)
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The NAKLimit0 Register (Host mode only) (HOST_NAKLIMIT0) is shown in Figure 83 and described in
Table 84 .
Figure 83. NAKLimit0 Register (Host mode only) (HOST_NAKLIMIT0)
7 5 4 0
Reserved EP0NAKLIMIT
R-0 R/W-0
LEGEND: R/W = Read/Write; R = Read only; - n = value after reset
Table 84. NAKLimit0 Register (Host mode only) (HOST_NAKLIMIT0) Field Descriptions
Bit Field Value Description
7-5 Reserved 0 Reserved
4-0 EP0NAKLIMIT 0-1Fh Sets the number of frames/microframes (high-speed transfers) after which Endpoint 0 should time
out on receiving a stream of NAK responses. The number of frames/microframes selected is 2
(—1)
(where m is the value set in the register, valid values 2-16). If the host receives NAK responses
from the target for more frames than the number represented by the Limit set in this register, the
endpoint will be halted.
Note: A value of 0 or 1 disables the NAK timeout function.
The Transmit Interval Register (Host mode only) (HOST_TXINTERVAL) is shown in Figure 84 and
described in Table 85 .
Figure 84. Transmit Interval Register (Host mode only) (HOST_TXINTERVAL)
7 0
POLINTVL_NAKLIMIT
R/W-0
LEGEND: R/W = Read/Write; - n = value after reset
Table 85. Transmit Interval Register (Host mode only) (HOST_TXINTERVAL) Field Descriptions
Bit Field Value Description
7-0 POLINTVL_NAKLIMIT 0-FFh For Interrupt and Isochronous transfers, defines the polling interval for the
currently-selected transmit endpoint. For Bulk endpoints, this register sets the number of
frames/microframes after which the endpoint should timeout on receiving a stream of NAK
responses There is a transmit Interval register for each configured transmit endpoint
(except Endpoint 0). In each case the value that is set defines a number of
frames/microframes (High Speed transfers), as follows:
Transfer Type Speed Valid values (m) Interpretation
Interrupt Low Speed or Full Speed 1 - 255 Polling interval is m frames
High Speed 1 - 16 Polling interval is 2
(—1)
microframes
Isochronous Full Speed or High Speed 1 - 16 Polling interval is 2
(—1)
frames/microframes
Bulk Full Speed or High Speed 2 - 16 NAK Limit is 2
(—1)
frames/microframes
Note: A value of 0 or 1 disables the NAK timeout function.
130 Universal Serial Bus (USB) Controller SPRUGH3 – November 2008
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