Till (= until) has an extra sense in Irish English that means something like ‘in order that’ or ‘so that [someone] can…’. A doting relative, upon meeting you after a long absence, might say ‘Come here till I see you’, which means ‘Come closer so that I can look at you properly’.
Raymond Hickey, in his essay Southern Irish English, gives the example ‘Come here till I tell you.’ This common expression can invite a listener who is within earshot to move physically closer, but it doesn’t always: it can also serve simply to announce an item of discourse, to prepare an audience’s ears for something of interest or significance, e.g.:
Come here till I tell you what happened this morning.
Used this way, Come here till I tell you is like a longer version of Old English Hwæt! (Hark!, Lo!, Listen!, etc.; literally What!), signalling the beginning of a story, albeit usually shorter than Beowulf. Some speakers run ‘Come here till’ together so it sounds like ‘C’meertle’.
T. P. Dolan has a nice entry in his Dictionary of Hiberno-English, in which he says till reflects the wider meaning of go /gʌ/ — the corresponding conjunction in Irish — and the idiom behaves ‘as if it were an adverbial clause of purpose’.
You can see how it works in the literary examples he provides:
Where is he till I murder him? (James Joyce, Ulysses)
Come here till I embrace you. (Samuel Beckett, Waiting for Godot)
Tell me who’s to blame will yeh til I tear his friggin’ head off. (Billy Roche, A Handful of Stars)
Come here till I comb your hair. (Frank McCourt, Angela’s Ashes)
And a few more from Google Books:
‘You killed my brother,’ said the giant; ‘come here, till I make a garter of your body.’ (J. M. Synge, The Aran Island)
‘Och, captain, avick! och! och! come here till I eat you!’ And she flung her arm round Robinson’s neck, and bestowed a little furious kiss on him. (Charles Reade, It Is Never Too Late to Mend)
Give me yer blissin’ till I go away to push me fortune. (Seumas MacManus, ‘Twas in Dhroll Donegal)
The MacManus line is one of several illustrative examples included in Michael Montgomery’s From Ulster to America: The Scotch-Irish Heritage of American English.
P. W. Joyce reported in 1910 that this till (‘in order that’) was used in many parts of Ireland. Certainly it was familiar to me growing up in the west, and I still hear and use it from time to time.
Elizabeth McGuane adds the related Come here to me and Come here to me now till I tell you. Ronan Delaney believes it’s ‘all down to that full Irish construction Gabh i leigth anseo go… or roughly Goile’nseo go…’
John Byrne says C’mere till I tell you a question is an ‘old Limerickism’, while Sally Tipper says the post got her thinking about the ‘northern English use of while to mean till‘, as in ‘I’ll not be back while late’; she can’t vouch for all contexts, so maybe a native can shed light.