.write_fe4e JSR tube_get \ Get the parameter from the parasite for the command: \ \ =write_fe4e(value) \ \ and store it as follows: \ \ * A = new value for the interrupt register STA VIA+&4E \ Set 6522 System VIA interrupt enable register IER \ (SHEILA &4E) to the new value JMP tube_put \ Send A back to the parasite and return from the \ subroutine using a tail callName: write_fe4e [Show more] Type: Subroutine Category: Keyboard Summary: Implement the write_fe4e command (update the System VIA interrupt enable register)Context: See this subroutine in context in the source code References: This subroutine is called as follows: * tube_table calls write_fe4e
This routine is run when the parasite sends a write_fe4e command. It updates the System VIA interrupt enable register in the I/O processor to the value sent by the parasite, and returns that value back to the parasite once the register has been set, so the parasite can know when the register has been updated.
Configuration variable: VIA = &FE00
Memory-mapped space for accessing internal hardware, such as the video ULA, 6845 CRTC and 6522 VIAs (also known as SHEILA)
As the I/O processor, fetch a byte that's been sent over the Tube from the parasite
As the I/O processor, send a byte across the Tube to the parasite