AppleWin Debugger Tutorial

Breakpoints

You now have a variety of options when specifying a breakpoint. Breakpoints can also be disabled, and later re-enabled. This lets ones set a bunch of breakpoints, and quickly re-activate them without having to re-enter the breakpoint logic.

Command	Effect
BPA r [op] value	Adds (conditional) Breakpoint. Default operator is equal ‘=’ (In a future version, will dispatch to BPX, BPR, BPP, or BPIO.)
BPX BPX expression BPX address[,len] BPX [op] symbol	Add Breakpoint trigger to stop executing when the PC is within the range of the Address, Symbol, or Expression. i.e. Range is: [addr,addr+len) Default length is 1. Default comparison operator is equal ‘=’
BP	Currently an Alias for BPX. (In a future version, will also support Loading and Saving of breakpoints.)
BPM address[,len]	Add Breakpoint trigger when memory is accessed by CPU or hard disk controller's DMA.
BPMR address[,len]	Add Breakpoint trigger when memory is read by CPU or hard disk controller's DMA.
BPMW address[,len]	Add Breakpoint trigger when memory is written by CPU or hard disk controller's DMA.
BPR reg [op] value	Add Breakpoint trigger when Register’s ‘reg’ value is compared to the Value.
BPV vpos[,len]	Add Breakpoint trigger when video-scanner's vertical position matches vpos. (NB. Auto-disable when hit.)
BPD #	Disable Breakpoint (grayed out).
BPE #	Enable Breakpoint (colored red).
BPC #	Clear specified Breakpoint. Note: The asterisk ‘*’ may be used to clear all breakpoints.
BPL	List Breakpoints.
BPIO	(In a future version, will add Breakpoint trigger on memory read or write.)
BPP	(In a future version, will add Breakpoint trigger on specific flag cleared or set.)
BRK [0\|1\|2\|3\|all] [on\|off]	Break on BRK or Invalid 1-3 byte opcodes
BRKOP [opcode]	Break on Opcode
BRKINT [on\|off]	Break on Interrupt

The general format for the conditional breakpoint is:

BPA register [operator] value.

You can use the following comparison operators:

Op	Name	Effect
=	Equal	Break when register is equal to value.
!	Not Equal	Break when register is not equal to value.
<	Less Than	Break when register is less than value.
>	Greater Than	Break when register is greater than value.
<=	Less Than or Equal	Break when register is less than or equal to value.
>=	Greater Than or Equal	Break when register is greater than or equal to value.

Breaking on any of the 6502 registers is fully supported:

Reg	Name	Effect
A	Accumulator	Break when Accumulator is triggered.
X	Register X	Break when Index X is triggered.
Y	Register Y	Break when Index Y is triggered.
PC	Program Counter	Break when PC is triggered.
S	Stack Pointer	Break when Stack Pointer is triggered.
P	Processor Status (flags)	Break when flags are triggered.

Notes:

BPP, Breaking on a specific flag (either set, or cleared) is forthcoming in a future version.

You can use the following optional address prefixes (each delimited by a "/" or forward-slash):

Prefix	Name	Effect
s<n>	Slot	Specify slot 0-7 for Saturn card.
<nnn>	Bank number	Specify bank 00 (main) 01-100 for RamWorks card's 64K bank or 0-7 for Saturn card's 16K bank.
l<1\|2>	Language Card 4K bank 1 or 2	Specify language card 4K bank.
rom	ROM	Specify ROM. (Can't be used with other prefixes.)

Notes:

The order of prefixes doesn't matter, and prefixes are case-insensitive.
In the image above, prefixing the blue "M" are the bank number (white "01") and LC bank (green "2"), and after the address range is a green "R" meaning trigger on-read. So this breakpoint was set using 'BPMR 01/L2/D000,1000'

Examples:

Input	Effect
BPX < FA62	Add Breakpoint when PC < $FA62.
BPR PC < D000	Add Breakpoint when PC < $D000.
BPR A 0	Add Breakpoint when Accumulator is zero.
BPR A ! 0	Add Breakpoint when Accumulator is not* zero.*
BPR S < 1FF	Add Breakpoint when Stack has had something pushed onto it.
BPV A0	Add Breakpoint when video-scanner is at line 160 ($A0) which is the start of the MIXED area.
BRK ON	Break execution when the opcode to be executed is $00 (ie. BRK).
BRK ALL ON	Break execution when the opcode to be executed is $00 (ie. BRK) or any Invalid opcode.
BRK 0 OFF	Disable breaking execution when the opcode to be executed is $00 (ie. BRK).
BRKOP 6C	Break execution when the opcode to be executed is $6C (ie. JMP (ABS)).
BRKINT ON	Break execution just after an interrupt occurs.
BPM E000,2000	Add breakpoint when an access occurs to main or aux memory or ROM in the range $E000-FFFF.
BP 00/L1/D000	Add breakpoint when PC = main memory language card's 4K bank 1 at $D000.
BPMW 01/D000,1000	Add breakpoint when a write occurs to aux memory (either 4K bank) in the range $D000-DFFF.
BP ROM/FF58	Add breakpoint when PC = ROM at $FF58.
BPM S3/7/L1/D800	Add breakpoint when an access occurs to slot 3's Saturn card's 16K bank 7, 4K bank 1 at $D800.