Hi Techies, Presently we are working on LPC2468 OEM Board for isochronus transfer in USB Device.
Can anybody exaplains the hardware behaviour(Registers use) with isochronus data transfer for IN and OUT in LPC2468.
Our quiries are 1.When we configure the Endpoints (IN or OUT) as Isochronus then how can we know that which Endpoint is received/transmition (was success for IN)the data?
User manual is explaining that we get the FRAME interrupt for isochronus Endpoint, but after getting the frame interrupt what we have to do?
2. What is the use of Start of Frame (11 bits) value? How can we use it?What information it contains?
Above example code also supports DMA using conditional compilation. Search "#if USB_DMA #endif" pair on the example code. The example code will help you to understand the description on the datasheet.
The usbcfg.h defines the keys.
usbcfg.h #define USB_DMA 0 #define USB_DMA_EP 0x00000040
Modify it directly OR apply uVision Config wizard to usbcfg.h to enable DMA on the isoc EPs
There are several scheme for the synchronization of isoc EP. Above example applies synchronized EP, popular for PCM audio. In this scheme, the number of the data on a packet represents the sampling rate.
For example, when the sampling rate is 8kHz, each packet has 8 pairs of data for each channel. To represent fractional sampling rate, say 44.1kHz, packets with 44 or 45 pairs are used. Usually, 44 pairs are transferred, but 45 pairs are sent every 10 transfers. 44 * 9/10 + 45 * 1/10 = 44.1
This requirement makes the DMA descriptor complicated.
Tsuneo