USB 2.0和USB 3.0的最大DMA缓冲区大小有何不同？

你好
根据我的理解，默认情况下，DMA缓冲区有256 KB内存可用。在我的应用中，我创建了两个DMA通道，每个通道具有计数＝1和大小＝USB数据包大小。此外，我想创建一个多DMA上行信道（2到1），使用剩余的所有可用内存。对于USB 3，对于正在工作的多通道信道，我使用计数＝126和大小＝1024（126×1024×2＝252 kb）。但是，当连接到USB 2主机时，我想使用计数＝252和大小＝512（252×512×2＝252 KB），但是DMALULTCONCHANNEICAtiON函数返回“16”，这意味着“CyuU3PyErrRoMeLyYyOrthError”。在尝试和错误之后，我发现USB 2的最大计数值似乎在80左右，这导致只有82 kb的缓冲区大小。这是什么原因呢？
-西尔维奥



     以下为原文
  Hello
     
    According to my understanding there is 256 kB memory available for DMA buffers by default. In my application I create two DMA channels each with count=1 and size = USB packet size. In addition, I want to create a MultiDMA upstream channel (2 to one) that uses all the remaining memory available. For USB 3.0 I am using count=126 and size=1024 (126*1024*2=252 kB) for the MultiDMA channel, which is working. However, when connected to a USB 2.0 host, I would like to use count=252 and size=512 (252*512*2=252 kB) but the DMAMUltiChannelCreate function returns "16" which means "CY_U3P_ERROR_MEMORY_ERROR". After some try and error, I found that maximum count value for USB 2.0 seems to be around 80, which results in only 82 kB buffer size. What can be the reason for this?
     
    -Silvio