ACXREG_ECPU_CTRL
CSR_SETB_2(sc, ACXREG_ECPU_CTRL, ACXRV_ECPU_HALT);
reg = CSR_READ_2(sc, ACXREG_ECPU_CTRL);
CSR_WRITE_2(sc, ACXREG_ECPU_CTRL, ACXRV_ECPU_START);