A Supreme Court judge has told a Sydney court a man who fatally stabbed his father after an argument over computer use is having a harder time in jail than other inmates due to his Asperger's syndrome.

Key points: Chapman's internet usage had been a long-standing source of conflict in the house

Chapman's internet usage had been a long-standing source of conflict in the house Prosecutors dropped a charge of murder after Chapman pleaded guilty to manslaughter

Prosecutors dropped a charge of murder after Chapman pleaded guilty to manslaughter The judge said both Chapman and his father likely suffered from Asperger's syndrome

Daniel Chapman was sentenced to six years behind bars over the incident at Moorebank in 2016, which happened after his father Stephen turned off the family modem at dinner time.

The court heard Daniel Chapman had been playing games online all day in his darkened room.

Justice Ian Harrison said both men likely suffered from Asperger's syndrome, and that the violence was not planned.

The judge said the condition meant Daniel Chapman found it difficult to pick up on social cues that were obvious to other inmates.

The court heard Chapman is in protective custody after being bashed in jail in January 2017.

He sustained a broken tooth, bruising and needed stitches to his lip after that attack.

Justice Harrison said the offender had been obsessed with computer games since he was eight and his excessive computer usage had been a source of conflict in the home.

He said on the day in question Chapman had no intent to kill his father.

"I am satisfied that Daniel Chapman was unable to control himself in a momentary lapse," he said.

Chapman was initially charged with murder but that charge was dropped after he pleaded guilty to manslaughter.

He said Chapman would find jail "more onerous and difficult to cope with than most other inmates" and that he had good prospects of complete rehabilitation.

Daniel Chapman's mother, Elaine Bell, was the most obvious and significant victim in this offence, Justice Harrison said.

He described the depth and breadth of her support for her Daniel as "unprecedented" and said her evidence, which had been entirely supportive of her son, "was not an easy thing" to give.

"I do not consider he is at risk of reoffending," Justice Harrison said.

Daniel Chapman will be eligible for parole in October 2019.