Aminadi was a prophet of God. At around 82 BC, his descendant, Amulek, tells us that he, Amulek, was the son Giddonah, who was the son of Ishmael, who was a descendant of Aminadi, the same Aminadi who interpreted the writing on the temple wall, which was written by the finger of the Lord.
What Amulek and, by extension, Mormon do not tell us is what was written on the wall, nor when or where it was written. Presumably, this was insider information, something Amulek's audience was already aware of.
The mere mention of Aminadi and his interpretation, without giving more information, shows that the incident was a sufficiently important historical event, whose details did not need rehearsing. However, the setting, time and message of the divine temple inscription might be recovered with the use of archeology. The following is something from the great Michael Coe:
Archeologist Marion Hatch and her Guatemalan colleagues have encountered evidence for the existance of a now-extinct lake around which the earthen platforms of Kaminaljuyu were arranged, as well as a sophisticated system of intensive agriculture. Connected with the lake were various irrigation canals, one of which carried water to an artificial storage basin 52.5ft(16m)wide and 36ft(11m) deep; leading from the latter were small tributary channels which brought water to the fields, some of which were agricultural terraces on the sides of the ravines. As the lake dried up about 200BC, perhaps due to overexploitation of the land, or even to tectonic movements(the region is highly earthquake-prone), the city dwindeled until its revival during the Early Classic period.(The Maya 7th Edition, pg 72)
So we have Amulek, Giddonah, Ishmael, X and Aminadi. Unlike Amulek and Giddonah who were "sons of", Ishmael is described as being a "descendent of" Aminadi. The missing generation(s), X, are at least one but maybe two in number. An independant researcher, Don Bradley, has shared with me a possible method for counting back to discover Aminadi's time.
If we count every generation, as 30 years, we have a five generations; ((5 * 30) + 82)) = 232.This puts the revelation to Aminadi, at the temple, at about 232 BC, around the time of the great draught at Kaminaljuyu, the presumed location of Nephi.
The Book of Jarom ends at 361 BC. Add five sequential record keepers later, as found in Omni, the last being Amaleki, who was born in the days of Mosiah I, and we have Mosiah I leaving the land of Nephi at around 211 BC. All of this places Aminadi, a Nephite, at the land of Nephi for the proper time.
So with the location being Nephi/Kaminaljuyu and the time being 232 BC, or perhaps a couple decades before, we can have a better sense of what the message was, a message of doom/repentance.
The only other recorded mention of the Lord writing on a wall, with his finger, was in the Book of Daniel, which also preceeded a then coming destruction. Hence the modern English idiom of "the writing's on the wall."
So while we can't be 100% certain of the exact years in which the draught/collapse, Mosiah migration and prophecy took place, they all seem to be happening within years of each other, pointing to their interelatedness.