CM108B Datasheet, PDF (17/24 Pages) C-Media Electronics – A Highly Integrated USB Audio Single Chip

CM108B
USB Audio Single Chip
7.4 Internal Registers
All of CM108B’s internal registers can be accessed via generic HID functional calls without the need to develop a
kernel mode driver. In total, 4 bytes of data can be read or written from the HID. The input report is for read and the
output report is for write. These internal registers of CM108B are used to control GPIO pins, S/PDIF output and
EEPROM data access.
Access via HID Class Command
HID interrupt will occur when HID_IR0-3 are updated by button status, or GPI in case HID_IR0[7:6] == 2’b00).
HID Get_Input_Report Format
Command Format:
bmRequestType
8’h A1
bRequest
8’h 01
(Get_Report)
wValue
16’h 01 00
(Rpt Type + Rpt ID)
wIndex
16’h 00 02
16’h 00 03
(Interface)
wLength
16’h 00 04
(4 bytes)
Data
Report
Input Data Format:
byte 0
byte1
byte2
byte3
HID IR0[7:0]
HID IR1[7:0]
HID IR2[7:0]
HID IR3[7:0]
HID Set_Output_Report Format
Command Format:
bmRequestType
8’h 21
bRequest
8’h 09
(Set_Report)
wValue
16’h 02 00
(Rpt Type + Rpt ID)
wIndex
16’h 00 02
16’h 00 03
(Interface)
wLength
16’h 00 04
(4 bytes)
Data
Report
Output Data Format:
byte 0
byte1
byte2
byte3
HID OR0[7:0]
HID OR1[7:0]
HID OR2[7:0]
HID OR3[7:0]
HID_IR0 (HID input report byte 0)
Offset: 0x00
Bits
Read/Write
Description
00: HID_IR1 is used as GPI,
7-6
R
10: values written to HID_IR0-3 are also mapped to
EPROM_DATA0-1 and EEPROM_CTRL
Others: reserved
5-4
R
Reserved
3
R
0: no activity on record/mute button
1: record/mute button pressed then released
2
R
0: no activity on playback/mute button
1: playback/mute button pressed then released
1
R
0: volume-down button released
Default
0x0
0x0
0x0
0x0
0x0
Datasheet Revision: 1.11
Page 17 / 24
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