Freescale Semiconductor MCF52277 Reference Manual page 388

Universal Serial Bus Interface – On-The-Go Module
Field
12–8 Scheduler health counter. These bits increment when the host controller fails to fill the TX latency FIFO to the
TXSCHHEALTH level programmed by TXFIFOTHRES before running out of time to send the packet before the next SOF.
This health counter measures the number of times this occurs to provide feedback to selecting a proper
TXSCHOH. Writing to this register clears the counter and this counter stops counting after reaching the
maximum of 31.
7–0 Scheduler overhead. These bits add an additional fixed offset to the schedule time estimator described as T
TXSCHOH As an approximation, the value chosen for this register should limit the number of back-off events captured in
the TXSCHHEALTH field to less than 10 per second in a highly utilized bus. Choosing a value too high for this
register is not desired as it can needlessly reduce USB utilization.
The time unit represented in this register is 1.267 μs when a device connects in high-speed mode.
The time unit represented in this register is 6.333 μs when a device connects in low-/full-speed mode.
For most applications, TXSCHOH can be set to 4 or less. A good value to begin with is:
Always rounded to the next higher integer. TimeUnit is 1.267 or 6.333 as noted earlier in this description. For
example, if TXFIFOTHRES is 5 and BURSTSIZE is 8, set TXSCHOH to 5×(8×4)/(40×1.267) equals 4 for a
high-speed link. If this value of TXSCHOH results in a TXSCHHEALTH count of 0 per second, low the value
by 1 if optimizing performance is desired. If TXSCHHEALTH exceeds 10 per second, raise the value by 1.
If streaming mode is disabled via the USBMODE register, treat TXFIFOTHRES as the maximum value for
purposes of the TXSCHOH calculation.
20.3.4.12 Configure Flag Register (CONFIGFLAG)
This EHCI register is not used in this implementation. A read from this register returns a constant of a
0x0000_0001 to indicate that all port routings default to this host controller.
Address: 0xFC0B_0180 (CONFIGFLAG)
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12
R 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
W
Reset 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
Field
31–0 Reserved. (0x0000_0001, all port routings default to this host)
20.3.4.13 Port Status and Control Registers (PORTSCn)
The USB module contains a single PORTSC register. This register only resets when power is initially
applied or in response to a controller reset. Initial conditions of a port are:
• No device connected
• Port disabled
20-30
Table 20-30. TXFILLTUNING Field Descriptions (continued)
TXFIFOTHRES
------------------------------------------------------------------------------------------- -
Figure 20-27. Configure Flag Register (CONFIGFLAG)
Table 20-31. CONFIGFLAG Field Descriptions
MCF52277 Reference Manual, Rev. 1
Description
× ( × )
BURSTSIZE 4
×
40 TimeUnit
11
0 0
0 0
Description
Access: User read-only
10 9 8 7 6 5 4 3
0 0 0 0 0 0 0 0 0 0 1
0 0 0 0 0 0 0 0 0 0 1
Freescale Semiconductor
.
ff
Eqn. 20-1
2 1 0