I'm preparing to teach Shakespeare's Henry V to a student. In III,ii, Pistol says


"The plainsong" is most just, for humors do abound.
Knocks go and come. God's vassals drop and die,

[then, singing]
And sword and shield
In bloody field
Doth win immortal fame"

Does anyone recognize this as an Office Hymn (say, for a martyr?) in either the Roman or Sarum Rite given that this is set in the early 1400's?
Failing that, does anyone know what melody might have been used?

Pistol continues later, in the same scene,

"If wishes would prevail with me,
My purpose should to fail with thee,
But thither would I hie.

and then "boy" picks up the tune.

As duly
But not as truly,
As bird doth sing on bough."


This appears to be more a secular tune, to match the secular words?

Any help, anyone?