CM118B Datasheet, PDF (18/25 Pages) C-Media Electronics – Highly Integrated & Configurable USB Audio Single Chip

CM118B
Highly Integrated & Configurable USB Audio Single Chip
Interrupt in Endpoint Descriptor
5.
Offset
Field
Size
0
bLength
1
1
bDescriptorType
1
2
bEndpointAddress
1
3
bmAttributes
1
4
wMaxPacketSize
2
6
bInterval
1
Value(Hex)
07
05
87
03
0004
2
Description
Total 7 bytes
ENDPOINT descriptor type
IN Endpoint
Endpoint number=3
Interrupt endpoint type
Maximum packet size: 4 bytes
2ms
4.6 Internal Registers
All internal registers of the CM118B can be accessed via generic HID functional calls without the need to
develop kernel mode driver. Total of 4bytes of data can be read or write from HID. Input report is for read while
output report is for write. Internal registers of the CM118B are used to control GPIO, S/PDIF output, EEPROM and
MCU data access. Host side HID or external MCU can access t h e CM118B internal registers. With both sides
accessed to the same set of registers, two-way communication can be achieved.
4.6.1 Access via HID Class Command
HID interrupt will occur when HID_IR0-3 are updated by button status, or updated by MCU (and GPI in
case HID_IR0[7:6] == 2’b00).
HID Get_Input_Report Format
Command Format:
bmRequestType bRequest
8’h A1
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
HID IR0[7:0]
byte1
HID IR1[7:0]
byte2
HID IR2[7:0]
byte3
HID IR3[7:0]
Datasheet Revision: 1.00
Page 18 / 25
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