ethernet auto-negotiation blocked?

Hi, I'm building a data acquisition and transfer system using Ethernet. The data source is continuous and has a throughput of 160 Mbps. Since the onboard Ethernet only supports 10/100 Base-T, I'm considering to use onboard SDRAM to store a block of data and then transfer to PC over Ethernet. I use DMA to write data in SDRAM and then use UDP to transfer data. The heap and stack are located in SDRAM, so the offset of SDRAM for data register will cause some exceptions. The onboard SDRAM has the size of 32M*8-bit. For example, （1） when I write SDRAM at 0x00001000 away from the base address of SDRAM, only 16kB data can be written into SDRAM； （2） when I write SDRAM　ａｔ　0x00004000 away from the base address of SDRAM, the system will be blocked at Ethernet auto-negotiation; (3) when I write SDRAM at 0x00010000, then 1MB data can be written into SDRAM. Sometimes, it will give me the error information like Ethernet exit. I don't know the reason to cause such phenomenon. Any ideas or suggestion are welcome! Thank you in advance!