How to extend the address size of ExtMem

[zxhero]

Hi,
I want to use 512MB address space of PS memory, instead of using upper address space of 512MB in default configuration. So what need I do to extend the address size of ExtMem from 0x10000000 to 0x20000000.
Thanks a lot!

[zxhero]

I set
class ExperimentConfig extends Config(new BaseSubsystemConfig().alter((site,here,up) => {
case DTSModel => "freechips,rocketchip-unknown"
case DTSCompat => Nil
case DTSTimebase => BigInt(1000000) // 1 MHz
case NExtTopInterrupts => 2
case ExtMem => MasterPortParams(
base = x"8000_0000",
size = x"4000_0000",
beatBytes = site(MemoryBusKey).beatBytes,
idBits = 4)
case ExtBus => MasterPortParams(
base = x"6000_0000",
size = x"2000_0000",
beatBytes = site(MemoryBusKey).beatBytes,
idBits = 4)
case ExtIn => SlavePortParams(beatBytes = 8, idBits = 8, sourceBits = 4)
}))
and in rocketchip_wrapper
assign S_AXI_araddr = {2'b0,mem_araddr[29:0]};
assign S_AXI_awaddr = {2'b0,mem_araddr[29:0]};

When I changed load address of pk to 0x90000000 instead of 0x8000000, and run ./fesvr-zynq pk hello, the program stuck somewhere. I don't know what's wrong with the load address. Do I need to change other places? I doubt this is because the start address of rom in rocketchip is 0x8000000 or fesvr-zynq thinks the load address of pk is 0x80000000.

I use zc706.