Hi, Have you check the AN65974? It implements a 2 way communication over bulk endpoint. You can test this, and then modify it to make the endpoints as ISOC. I see that you have changed the DMA to multi type, but it depends on the application. If you are having one USB EP and one GPIF socket, then you should use normal DMA channel. The invalid sequence error may come, when you are using a multi channel DMA and you are not filling the PROD socket in round-robin fashion (which is required in Multi channels). Best way I would suggest is to start with the slave fifo applcaiton note using the bulk endpoint and then change to ISOC. You can also create a tech support case if further assistance is required.