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Universal Serial Bus (USB)
MCF5272 ColdFire Integrated Microprocessor User’s Manual, Rev. 3
12-10
Freescale Semiconductor
12.3.2.3
USB Real-Time Frame Monitor Register (RFMR)
The value in the RFMR can be used to determine approximately how much time has elapsed since the USB
host sent its last start-of-frame packet.
Because the hardware does not guarantee that any of the bit values are stable during the read access:
only the higher-order bits should be used
the returned data should always be de-glitched by verifying that the same value is seen on the
higher-order bits for two consecutive read cycles.
Figure 12-5 shows the USB real-time frame monitor register.
Figure 12-5. USB Real-Time Frame Monitor Register (RFMR)
Table 12-5 lists field descriptions for the USB real-time frame monitor register.
15
14
13
0
Field
—
RTFM
Reset
0000_0000_0000_0000
R/W
Read
Addr
MBAR + 0x100A
Table 12-5. RFMR Field Descriptions
Bits
Name
Description
15–14
—
Reserved, should be cleared.
13–0
RTFM
Real-time frame count. Contains the current USB frame counter value. The counter is incremented one
time for every USB bit time and is reset when a SOF packet from the host is detected or an artificial start
of frame (ASOF) interrupt is generated.