index. This constitutes the second phase of the three-phase CONTROL transfer.
The core Packetizes the data into multiple data transfers as necessary.
4. Automatically checks for errors and re-transmits data packets if necessary.
5. Responds to the third (handshake) phase of the CONTROL transfer to terminate
the operation.
The Setup Data Pointer can be used for any Get_Descriptor request; for example,
Get_Descriptor-String. It can also be used for vendor-specific requests (that you define),
as long as bytes 6-7 contain the number of bytes in the transfer (for step 1).
It is possible for the 8051 to do manual CONTROL transfers, directly loading the
IN0BUF buffer with the various packets and keeping track of which SETUP phase is in
effect. This would be a good USB training exercise, but not necessary due to the hardware
support built into the EZ-USB core for CONTROL transfers.
For DATA stage transfers of fewer than 64 bytes, moving the data into the IN0BUF buffer
and then loading the EP0INBC register with the byte count would be equivalent to loading
the Setup Data Pointer. However, this would waste 8051 overhead because the Setup Data
Pointer requires no byte transfers into the IN0BUF buffer.
7.3.4.2
Get Descriptor-Configuration
Table 7-11. Get Descriptor-Configuration
Byte
Field
bmRequestType
bRequest
Value
Meaning
8051 Response
Set SUDPTR H-L to start of
Configuration Descriptor table in
RAM
0
1
2
3
0x80 IN, Device
0x06 “Get_Descriptor”
CFG Config Number
wValueL
wValueH
0x02 Descriptor Type:
Configuration
4
5
6
7
wIndexL
wIndexH
wLengthL
wLengthH
0x00
0x00
LenL
LenH
EZ-USB TRM v1.9
Chapter 7. EZ-USB CPU
Page 7-15
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