Universal Serial Bus (USB)
18-30
Am186™CC/CH/CU Microcontrollers User’s Manual
18.5.11.1
USB Command Processing and the Interrupt Endpoint
When a SET_CONFIGURATION or SET_INTERFACE command is received, software
must reprogram the Interrupt Endpoint Definition registers (if necessary) to reflect the new
configuration and alternate interface setting. Also, the descriptor relating to the interrupt
endpoint (which is returned to a host GET_DESCRIPTOR request) must contain the correct
maximum packet size (8 or 16 bytes) and Interval value (1-ms to 255-ms interrupt rate).
18.5.11.2
Data Transfer with the Interrupt Endpoint
The interrupt endpoint can be used in two different ways. If the amount of data to be
transferred on each interrupt is less than or equal to the maximum packet size, each packet
sent to the host constitutes an entire transaction. If the amount of data to be transferred on
each interrupt exceeds the maximum packet size, an interrupt can consist of multiple
packets. In this case, each packet except the last one must be MaxPacketSize bytes.
Transferring a number of bytes between 0 and MaxPacketSize – 1 (inclusive) denotes the
end of the transaction. If a large number of bytes are to be transferred on each interrupt, it
is strongly suggested that the maximum packet size be set to 16, because this makes more
efficient use of the USB bandwidth than a setting of 8.
18.5.11.3
Interrupt Endpoint Interrupts
The ACT_REQ bit is reflected in the UISTAT1 register as the INT_EP_ACT bit. Software
can mask off this interrupt in the UIMASK1 register.
18.5.12
Endpoint Definitions
The USB specification provides for endpoints to be grouped into interfaces. Multiple
interfaces that do not share endpoints can be grouped into configurations, and a device
can have multiple configurations, only one of which can be in use at any one time. In the
Am186CC and Am186CU microcontrollers, software assigns each of the endpoints (other
than the control endpoint, which has a number of 0 and appears in every interface) an
endpoint number, interface number, configuration number, alternate setting number, Max
Packet Size, and direction.
The
USB Specification, Version 1.0 defines the endpoint configuration process:
“Host software should only set configuration and interface values that match a device
descriptor returned by the device in response to a GET_DESCRIPTOR command.
However, the USB hardware accepts as valid any configuration or feature setting in the
range of 0d to 3d, regardless of the available descriptors. To help ensure reliable operation
in any USB environment, device software can define a minimal descriptor (i.e., Endpoint 0
with no bandwidth allocation) for any configuration and interface settings that it does not
define otherwise.”
18.5.12.1
Control Endpoint Definition
The control endpoint features are not programmable as are the other endpoints. This
endpoint is common to, and is required by, all USB device class specifications. Table 18-7
lists the control endpoint parameters.
The control endpoint (endpoint 0) is always considered to be a member of all device
configurations, a member of all interfaces present in a device configuration, and a member
of all alternate settings of any given interface.
Содержание Am186 CC
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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...