Cytidylyltransferase required for protein O-linked mannosylation (PubMed:22522420, PubMed:22522421, PubMed:26687144, PubMed:26923585, PubMed:27130732, PubMed:27601598). Catalyzes the formation of CDP-ribitol nucleotide sugar from D-ribitol 5-phosphate (PubMed:26687144, PubMed:26923585, PubMed:27130732). CDP-ribitol is a substrate of FKTN during the biosynthesis of the phosphorylated O- mannosyl trisaccharide (N-acetylgalactosamine-beta-3-N- acetylglucosamine-beta-4-(phosphate-6-)mannose), a carbohydrate structure present in alpha-dystroglycan (DAG1), which is required for binding laminin G-like domain-containing extracellular proteins with high affinity (PubMed:26687144, PubMed:26923585, PubMed:27130732). Shows activity toward other pentose phosphate sugars and mediates formation of CDP-ribulose or CDP-ribose using CTP and ribulose-5- phosphate or ribose-5-phosphate, respectively (PubMed:26687144). Not Involved in dolichol production (PubMed:26687144). {ECO:0000269|PubMed:22522420, ECO:0000269|PubMed:22522421, ECO:0000269|PubMed:26687144, ECO:0000269|PubMed:26923585, ECO:0000269|PubMed:27130732, ECO:0000269|PubMed:27601598}. This is the function of Ensembl gene identifier ENSG00000214960 (CRPPA, CDP-L-ribitol pyrophosphorylase A).