surname help

[Bryan]

I'm looking for information on the surname Erwin. I can't seem to find any definitive source of the name, but I believe it is either Scottish or northern Irish. According to George F. Blacks The Surnames of Scotland:

"Irvine: of territorial origin, Irving in Dumfriesshire and Irvine in Ayrshire; the Dumfriesshire parish was the chief source of the name; the charter of the Barony of Drum dates from1324; an offshoot of the Aberdeenshire family appears in Shetland in the mid-1500s; in Northern Ireland, the name has become confused with the Irish Erwin."

Most other sources claim it is Scottish and one even said it's Welsh. Anyone have any ideas?