【实战经验】HID与音频冲突问题

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zero99 发布时间：2016-11-18 16:30

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前言
Demo 程序中，HID 和 Audio 单独运行都不会有问题，把 HID 和 Audio 整合在一起，同进传送数据时，会出现Audio 不能传送数据的情况。

根本原因

基本情况：
         1. 当增加HID 的传输频率时，这种情况更容易出现。
         2. 当HID 包在帧开始时，不会出现这个问题。
根本原因是相关的参考手册中描述的一个已知的问题。
                  35.13.8 Worst case response time
                  When the OTG_HS controller acts as a device, there is a worst case response time for any
                  tokens that follow an isochronous OUT. This worst case response time depends on the AHB
                  clock frequency.
                  The core registers are in the AHB domain, and the core does not accept another token
                  before updating these register values. The worst case is for any token following an
                  isochronous OUT, because for an isochronous transaction, there is no handshake and the
                  next token could come sooner. This worst case value is 7 PHY clocks when the AHB clock
                  is the same as the PHY clock. When the AHB clock is faster, this value is smaller.
                  If this worst case condition occurs, the core responds to bulk/interrupt tokens with a NAK
                  and drops isochronous and SETUP tokens. The host interprets this as a timeout condition
                  for SETUP and retries the SETUP packet. For isochronous transfers, the Incomplete
                  isochronous IN transfer interrupt (IISOIXFR) and Incomplete isochronous OUT transfer
                  interrupt (IISOOXFR) inform the application that isochronous IN/OUT packets were
                  dropped.
因此，建议在帧开始的时候或帧结束前开始发送HID 数据包。

解决方案：
            1. 在帧开始的时候发送数据。
            2. 在帧80%，85%，90%，95%时发送数据。通过设置
            #define DCFG_FRAME_INTERVAL_80                      0
            #define DCFG_FRAME_INTERVAL_85                      1
            #define DCFG_FRAME_INTERVAL_90                      2
            #define DCFG_FRAME_INTERVAL_95                      3

            USBx_DEVICE->DCFG |= DCFG_FRAME_INTERVAL_80;

         RM0090
            34.16.4 Device-mode registers
            OTG_FS device configuration register (OTG_FS_DCFG)

                  Bits 12:11 PFIVL: Periodic frame interval
                  Indicates the time within a frame at which the application must be notified using
                  the end of
                  periodic frame interrupt. This can be used to determine if all the isochronous
                  traffic for that
                  frame is complete.
                  00: 80% of the frame interval
                  01: 85% of the frame interval
                  10: 90% of the frame interval
                  11: 95% of the frame interval