Universal Serial Bus (USB)
18-24
Am186™CC/CH/CU Microcontrollers User’s Manual
Isochronous synchronization involves converting the data stream from its sample rate (for
example, the 44.1-KHz rate of an audio CD player) into packets delivered at the fixed USB
start-of-frame (SOF) rate of 1 KHz (1000 frames per second). The USB specification defines
three types of isochronous synchronization:
■
Asynchronous: The data sample clock and the USB frame rate are independent of
each other. It is up to the host’s device driver and device software to convert the data
rate as needed. For example, a receiving endpoint’s software (host or device) can provide
feedback so the transmitting endpoint’s software can adjust the amount of isochronous
data sent in each frame.
■
Synchronous: The data sample rate is synchronized with the USB SOF rate so the
same amount of isochronous data can be transmitted in every frame. There are two
ways to achieve this:
– Lock the data source sample clock to the USB SOF rate. For example, a design can
route the microcontroller’s USBSOF output through a PLL to drive the sample clock
of an external codec. For more about the USBSOF signal, see “Isochronous
Synchronization Signals” on page 18-6.
– Request USB master client capability (through the USB driver basic host interface)
and then adjust the USB SOF rate to keep it synchronized with the sample clock. Only
one device can be the master client at a time, so devices that use this method must
be able to operate asynchronously if master client capability is denied.
■
Adaptive: The data sample clock can be freely adjusted to receive or transmit data at
any rate within a given range. The microcontroller’s Auto Rate feature (described in the
following section) allows isochronous IN endpoints to implement adaptive
synchronization with a variety of input sources.
The type of synchronization to use for an isochronous endpoint depends on the design
requirements and capabilities of the peripheral device. All of these synchronization types
make use of USB peripheral controller features described in the following section.
18.5.8
Isochronous Transfer Features
The USB peripheral controller provides full support for the Isochronous transfer type while
minimizing system resource overhead. A USB peripheral device using the Am186CC or
Am186CU microcontroller can easily support the isochronous data transfer in the IN
direction as an asynchronous, synchronous, or adaptive synchronous data source. These
features combined with the other integrated communications devices and DMA controller
allow many different communications and audio devices to be built with this device. The
following microcontroller features are provided to support isochronous transfers:
■
Missing-SOF Detection: The USB peripheral controller implements an adaptive
missing-SOF detection mechanism. A missing SOF packet is detected when the current
USB frame length is six USB bit times greater than the last frame in which a SOF packet
was successfully received.
Hardware indicates a missing SOF by setting the UISTAT2 register’s MS_SOF bit, which
software can enable as an interrupt source by setting the corresponding bit in the
UIMASK2 register.
■
SOF Generation: Whenever an SOF is detected, hardware sets the UISTAT2 register’s
SOF_GEN bit, which software can enable as an interrupt source by setting the
corresponding bit in the UIMASK2 register.
Summary of Contents for Am186 CC
Page 1: ...Am186 CC CH CU Microcontrollers User s Manual Order 21914B...
Page 4: ...iv Am186 CC CH CU Microcontrollers User s Manual...
Page 18: ...Table of Contents xviii Am186 CC CH CU Microcontrollers User s Manual...
Page 24: ...Introduction xxiv Am186 CC CH CU Microcontrollers User s Manual...
Page 40: ...Architectural Overview 1 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 86: ...System Overview 3 36 Am186 CC CH CU Microcontrollers User s Manual...
Page 92: ...Emulator Support 4 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 112: ...DRAM Controller 6 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 134: ...Interrupts 7 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 186: ...Programmable I O Signals 9 8 Am186 CC CH CU Microcontrollers User s Manual...
Page 200: ...Watchdog Timer 11 6 Am186 CC CH CU Microcontrollers User s Manual...
Page 232: ...Asynchronous Serial Ports UARTs 13 24 Am186 CC CH CU Microcontrollers User s Manual...
Page 242: ...Synchronous Serial Port SSI 14 10 Am186 CC CH CU Microcontrollers User s Manual...
Page 264: ...High Level Data Link Control HDLC 15 22 Am186 CC CH CU Microcontrollers User s Manual...
Page 332: ...Universal Serial Bus USB 18 34 Am186 CC CH CU Microcontrollers User s Manual...
Page 348: ...Register Summary A 16 Am186 CC CH CU Microcontrollers User s Manual...
Page 376: ...Index Index 18 Am186 CC CH CU Microcontrollers User s Manual...