REX_PAGE1_GO
rex_write(dc, REX_PAGE1_GO, REX_P1REG_CFGSEL, REX_CFGSEL_VC1_SYSCTL);
rex_read(dc, REX_PAGE1_GO, REX_P1REG_VC1_ADDRDATA);
rex_write(dc, REX_PAGE1_GO, REX_P1REG_CFGSEL, REX_CFGSEL_VC1_SYSCTL);
rex_write(dc, REX_PAGE1_GO, REX_P1REG_VC1_ADDRDATA, val);
rex_read(dc, REX_PAGE1_GO, REX_P1REG_WCLOCKREV);