Universal Serial Bus (USB)
Am186™CC/CH/CU Microcontrollers User’s Manual
18-25
The SOF is also reflected on the controller’s USBSOF output signal, which is used in
the first method (lock the sample clock) of synchronous isochronous synchronization,
as described in “Isochronous Transfer Synchronization” on page 18-23.
If a missing SOF is detected, the USB peripheral controller automatically generates an
internal SOF, which is reflected by the SOF_GEN bit and the USBSOF signal. This allows
synchronous isochronous endpoints to remain locked to the USB clock even when the
SOF packet is corrupted on the bus.
■
USB Frame Position Monitoring: This allows the device software to detect any
difference between the sample rate of a data source and the USB frame rate. This is
required for an Isochronous IN endpoint that uses the second method (request USB
master client capability) for synchronous isochronous synchronization, as described in
“Isochronous Transfer Synchronization” on page 18-23.
In the Am186CC microcontroller, the SAM_CLK_SEL field in the ISCTL register can
select a sample rate clock source: either the USBSCI signal (on the UCLK pin) or the
frame synchronization signal used for HDLC Channel A, PCM Highway, and GCI.
During each USB frame, the FPMCNT register latches the USB frame position bit counter
after a specific number of source clocks are counted on the sample input. The value
latched in the FPMCNT register is the number of USB bit times counted during the source
clock interval specified in the BCNT_LRATE field of the ISCTL register (1–64 source
clocks, programmable in powers of two). Device software can compare these two values
to determine whether the USB frame rate and the source sample clock are moving
relative to each other.
If the device is granted master client capability, it is able to use the USB Device basic
host interface (defined in the USB specification) to gradually increase or decrease the
USB SOF rate to correct any drift with respect to the data source’s sample rate.
Whenever FPMCNT is updated, hardware sets the UISTAT2 register’s POS_UP bit,
which software can enable as an interrupt source by setting the corresponding bit in the
UIMASK2 register.
■
Auto Rate: This allows the designer to implement adaptive synchronization on an
isochronous IN endpoint using general-purpose DMA or SmartDMA to handle an
arbitrary data source rate. The Auto Rate feature uses the data source’s sample rate
clock (frame rate) as an input to automatically control the number of data bytes sent to
the USB host during each transaction.
In the Am186CC microcontroller, the SAM_CLK_SEL field in the ISCTL register can
select a sample rate clock source: either the USBSCI signal (on the UCLK pin) or the
frame synchronization clock (FSC) signal used for HDLC Channel A, PCM Highway, and
GCI.
The BYTES_SAM field in ISCTL sets the number of bytes to move per source clock
sample (1, 2, or 4 bytes). Also make sure that the Max Packet Size programmed for the
endpoint is greater than or equal to the largest number of data bytes that the endpoint
might need to move during a USB transaction.
After the sample clock source and bytes per sample are selected, set the
AUTO_RATE_EN bit in the xEPDEF3 register (where x = A, B, C, or D) to enable auto
rate for the endpoint.
CC
CC
Содержание Am186 CC
Страница 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Страница 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Страница 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Страница 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Страница 39: ...Architectural Overview Am186 CC CH CU Microcontrollers User s Manual 1 15 Figure 1 6 32 Channel Linecard CH CC...
Страница 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Страница 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Страница 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Страница 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Страница 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Страница 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Страница 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Страница 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Страница 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...