Field Name             Bits   Default   Description
ZPASS_ADDR             31:2   0x0       Writing this location with a DWORD address causes the
                                        value in ZB_ZPASS_DATA to be written to main
                                        memory at the location pointed to by this address.
                                        NOTE: R300 has 2 pixel pipes. Broadcasting this address
                                        causes both pipes to write their ZPASS value to the same
                                        address. There is no guarantee which pipe will write last.
                                        So when writing to this register, the GA needs to be
                                        programmed to send the write command to pipe 0. Then
                                        a different address needs to be written to pipe 1. Then
                                        both pipes should be enabled for further register writes.
