This composition, designated as a “soneto” by Valderrábano (Soneto V in pujol1965), is a setting of the opening couplet of a famous stanza (XVLIV, 61) from Orlando furioso by Ludovico Ariosto (1474-1533) that became a melodic-harmonic formula common in Italy in the sixteenth century for the recitation of verses in ottava rima. Gerbino and Silbiger (”Ruggiero” in Grove Online) point to the difficulty of establishing an exact harmonic or melodic profile for the formula given its widespread use in oral tradition and, consequently, the significant differences between surviving versions. The Valderrábano setting has some superficial relationship with the ruggiero scheme, but seems to be more of a freely composed setting rather than a recitation formula. Pujol’s edition is for a vihuela in G, but a vihuela in D would render the transcription is in G, more usual for ruggiero settings. In other Spanish sources the ruggiero formula is used by Ortiz in the Tratado de glosas (1553) without title, and also as the “Rugier, Glosado de Antonio de Cabezón” in Venegas de Henestrosa, no 120 (p. 190 Anglés edn) with the text “Rugier qual sempre fui tal esser voglio” See Ward/EditorialMethods 113.
Einstein (einstein1971) transcribe Ruffo’s version “io sempre fui” which has a different melody. Pujol’s commentary for this piece suggests that he had limited knowledge of the tradition of Italian ruggiero settings. The original Ariosto text is as follows:

Io son qual sempre fui, tal esser voglio
Fin a la morte, e piú, se piti si puote.
Immobil son di vera fede scoglio
Che d'ogn'intorno il mar l'aria percuote.

O siam'amor benigno o m'usi orgoglio,
O me fortun'in alto o in basso ruote,
Non mai gia per bonaccia ne per yerno
Loco mutai ne muteró in eterno.