******* BBSCAN USERS GUIDE *******

25/11/82    WRITTEN BY GEOFF HAYNES

1. PURPOSE
	THIS PROGRAM WAS WRITTEN TO VERIFY THE
	INTEGRITY OF 8" SINGLE DENSITY DISKETTES
	USING IBM SOFT SECTOR FORMAT. THIS VERSION
	IS SPECIFICALLY WRITTEN FOR THE 'BIGBOARD'
	MICROPROCESSOR BOARD.

	THE PROGRAM CAN BE USED BOTH FOR VERIFYING
	BLANK DISKS PRIOR TO USE, AND TO CHECK THE
	STATUS OF DISKS CONTAINING USER DATA, SINCE
	IT PERFORMS NO WRITING.

2. OPERATION
	FIRST, BBSCAN READS THE DIRECTORY SECTORS
	ON THE DISK BEING SCANNED, SO THAT IF ERRORS
	ARE DETECTED IN THE USER AREA, THEY WILL BE
	LINKED TO THE CORRESPONDING FILE NAME IF THAT
	SECTOR HAS BEEN ALLOCATED, AND THAT FILENAME
	WILL BE INCLUDED IN THE ERROR REPORT FOR THE
	FAILING SECTOR.
	IT THEN COMMENCES READING ALL SECTORS ON THE
	DISK. IF AN ERROR IS DETECTED, THE READ
	OPERATION FOR THAT SECTOR IS RETRIED UP TO 9
	MORE TIMES. IF THE SECTOR IS READ SUCCESSFULLY
	DURING RETRY, THE ERROR IS CONSIDERED TEMPORARY
	AND IS SO INDICATED IN THE ERROR REPORT.
	OTHERWISE THE ERROR IS REPORTED AS PERMANENT.
	THE ERROR REPORT DISPLAYS THE PHYSICAL TRACK
	AND SECTOR IN ERROR, THE TYPE OF ERROR,
	(I.E. TEMP OR PERM), THE STATUS BYTE RECEIVED
	FROM THE DISK CONTROLLER (AS DEFINED IN THE
	1771 FDC CHIP SPECS), AND THE DISPOSITION OF
	THE SECTOR (CP/M SECTOR, DIRECTORY SECTOR,
	UNALLOCATED SECTOR, OR THE ASSOCIATED FILE
	NAME IF ALLOCATED.

	IN ORDER TO DETERMINE WHETHER ERRORS ARE EITHER
	TEMPORARY OR PERMANENT, ALL DISK I/O MUST BYPASS
	BDOS, OTHERWISE TEMPORARY ERRORS WILL NOT BE
	DETECTED AT ALL, AND PERMANENT ONES WILL INVOKE
	THE INFAMOUS 'BDOS ERROR ON X: BAD SECTOR' MESSAGE.
	ADDITIONALLY, SINCE THE BIOS NORMALLY HANDLES
	THE ACTUAL RETRY DURING DISK READ/WRITE OPERATIONS,
	THE RETRY FUNCTION IN BIOS MUST ALSO BE BYPASSED,
	OR DISABLED BY DYNAMIC PATCHING, IN ORDER TO
	DETECT TEMPORARY ERRORS.

	IN THE CASE OF THE 'BIGBOARD', THE RETRY COUNT
	BYTE USED BY THE MONITOR IS LOADED BY BBSCAN,
	AND THE CALL TO THE READ ROUTINE IS DIRECTED
	TO A LOCATION PAST THE POINT WHERE THE ROUTINE
	INITIALIZES THE COUNT. IN THIS WAY, BBSCAN HAS
	FULL CONTROL OVER RETRY.

	BBSCAN PROCESSES EACH TRACK IN A PHYSICALLY
	SEQUENTIAL SECTOR SEQUENCE RATHER THAN THE
	CP/M 'LOGICALLY' SEQUENTIAL SEQUENCE. BY
	DOING THIS, THE ERROR REPORT CLEARLY INDICATES
	SCRATCHES ON THE MEDIA, BECAUSE THE SECTOR VALUE
	IS THE SAME ACROSS MULTIPLE TRACKS. THIS WOULD
	NOT BE OBVIOUS IN THE CASE OF A LOGICALLY
	SEQUENTIAL SCAN.

3. USING THE PROGRAM
	THE SOURCE FILE SHOULD REQUIRE NO MODIFICATION
	PRIOR TO ASSEMBLY. THIS RATHER BOLD STATEMENT
	ASSUMES THAT THE ROM-BASED MONITOR (PFM) IN
	YOUR SYSTEM IS THE SAME LEVEL AS THAT FOR
	WHICH THIS PROGRAM WAS DEVELOPED. THE VERSION
	ON THE DEVELOPMENT SYSTEM IS 3.3, DATED
	AUGUST 2, 1980. IF YOURS IS DIFFERENT, YOU
	SHOULD CHECK THE EQUATES AT THE START OF THE
	LISTING WHICH POINT INTO THE MONITOR.
	THE COMMENTS FIELD FOR THESE EQUATES INDICATES
	WHICH LABELS THEY REFER TO IN THE MONITOR
	LISTING 'ROM.PRN' WHICH COMES WITH THE BIGBOARD
	CP/M PACKAGE.

	THE PROGRAM MAY BE INVOKED IN THE FOLLOWING WAYS:
		A)  'BBSCAN'
	  OR    B)  'BBSCAN X' WHERE X=DRIVE NAME

	IN THE FIRST CASE, THE PROGRAM WILL EXECUTE ON
	THE CURRENTLY LOGGED DRIVE.
	IN THE SECOND CASE, IT WILL RUN ON THE DRIVE
	SPECIFIED BY 'X'