Forced power interruption during a write operation
			Nintendo Development Dept. 3
					Takayoshi Hashida


1. Symptoms

	When the user turns the power off during a write operation to the N64 
	Disk Drive, the contents of the block being written at that time can be
 	destroyed. The next time the block is read, one of two things can occur:

	i) An error 23 is generated.
	ii) No error is generated, but the data is destroyed.


	While either symptom can arise, there is no danger of damage to the dis
	or to the drive.  (For details, please see "3 - Countermeasures".)

	In the past, an error 24 could occur either when the power was cut or 
	for various reasons. Because of this, it was difficult to ascertain 
	whether the error was a temporary error (generated because the power was
 	cut during a write operation) or whether it was a fatal error - 
	requiring a fix.  With the installation of this patch, the only error 
	generated when the power is cut is an error 23.

	The same holds true when the disk is forcibly ejected during a write 
	operation, and the power is cut while the system is waiting for the disk
 	to be reinserted.(Please see Error Processing Sequences in section 10 of
 	the N64 Disk Drive Programming Manual).  


2. Detection

	Beware of symptom ii where no error is generated but the data is destroyed.  
	In this situation new data can be written to the front sectors in the block, but 
	the rest of the 85 sectors maintain their old data.

	Run a checksum for the game in order to detect when this occurs.


3. Countermeasures

	In the case of either symptom, the data cannot be recovered. However, it is possible 
	to rewrite the data and to continue to use the disk.  Since the disk is not destroyed,  
	there is no need to display an error message on the screen.

	For data rewrites, please make appropriate use of the initial values of saved data.

	Since the cause of an error 23 generated during a ROM area read might be different 
	than a power cutoff during a write operation, please display the error number and 
	prompt the user to read the manual.

	Although the message displayed states "the data cannot be recovered," it is possible 
	to recover the data using "mirroring," or the process of securing two save regions as 
	described in section 12.12 of the N64 Disk Drive Programming Manual.

