The New Pali Course Part III (1950)
Prof. A. P. Buddhadatta Maha Nayaka Thera

Chapter III Passive Forms

* haa (to decrease) + ya + ti = hiiyati, is decreased
* upa + maa (to measure) + ya + ti = upamiiyati, is compared

ii of the above is shortened when y of ya is doubled:
* upamiyyati (to be compared)
* daa (to give) + ya + ti = diyyati or diiyati

(d) The final i and u of the roots are lengthened before ya when y is not doubled:

* ni (to lead) + ya + ti = niiyati, niyyati
* ci (to collect) + ya + ti = ciiyati, ciyyati
* su (to hear) + ya + ti = suuyati, suyyati

(e) To the roots ending in uu the sign is added without any change:

* luu (to reap) + ya + ti = luuyati, is reaped
* bhuu (to be) + ya + ti = bhuuyati, is becoming

(f) The most common way to form passive bases is to insert an ii between the root and the sign ya:

* kara (to do) + ii + ya + ti = kariiyati, is done
* hasa (to laugh) + ii + ya + ti = hasiiyati, is laughed

(1) In some cases, ya is added to the active bases by means of ii:

root base
chidA > chinda + ii + ya + ti = chindiiyati
mucA > mu~nca + ii + ya + ti = mu~nciiyati
gahA > ga.nha + ii + ya + ti = ga.nhiiyati
rudhA > rundha + ii + ya + ti = rundhiiyati

YP: chindiiyati, is cut
YP: mu~nciiyati, is released
YP: ga.nhiiyati, is taken
YP: rundhiiyati, is hidden

ref: http://www.tipitaka.net/pali/synthesis/pali3.00.cdv

(to be continued...)