REX_P1REG_CFGSEL
rex_write(dc, REX_PAGE1_GO, REX_P1REG_CFGSEL, REX_CFGSEL_VC1_SYSCTL);
rex_write(dc, REX_PAGE1_GO, REX_P1REG_CFGSEL, REX_CFGSEL_VC1_SYSCTL);
rex_write(dc, REX_PAGE1_SET, REX_P1REG_CFGSEL, REX_CFGSEL_VC1_LADDR);