(1) Verbs ending in -u#, -a#. Juba verbs ending in -u# and in -a# are transitive in the majority of cases (e.g. jíbu 'bring', dáfa 'pay'). The derivation of a passive voice for this category of verbs implies a morphological marking which consists in a stress displacement whose outcomes vary according to the syllabic structure and the phono-morphological features of the verb (e.g. jíbu 'bring' vs. jibú [bring\PASS], kátulu 'kill' vs. katulú 'killed', ásma 'listen' vs. asmáo 'listened', dába 'slaughter' vs. dabaó 'slaughtered'). As regards the syntax, the subject of the active is often omitted; otherwise, it is placed in a peripheral position in comparison with the patient, which occupies the subject position when an agent is specified or when the passive is followed by a secondary verb (accusative phrase). In the case of impersonal or habitual phrases without agent the patient occupies a direct object position and follows the verb (ergative phrase).
(2) Verbs ending in -í#. These are morphologically invariable verbs which always have stress on the last syllable. So even if the patient always precedes the verb, the passive construction is not prototypical since there is no morphological marking. The agent is always absent.
Source: Manfredi 2005: 155
Source: Manfredi 2005: 155
Source: Manfredi 2005: 155
Source: Manfredi 2005: 156