JMP $1000 at the start of the file.
+65816 code can be tricky to disassemble for a number of reasons. +24-bit addresses are formed from 16-bit data-access operands by combining +with the Data Bank Register, which often requires a bit of manual +intervention. But the problems go beyond that. Consider the following +bit of source code for the Apple IIgs:
++rsrcmsg pea rsrcmsg2|-16 + pea rsrcmsg2 + _WriteCString + lda #buffer + sta pArcRead+$04 + lda #buffer|-16 + sta pArcRead+$06 ++
In both cases we're referencing a 24-bit address as two 16-bit values. +Without context, the disassembler will treat the PEA instruction as two +independent 16-bit addresses, and the immediate values as constants:
++ .dbank $02 +02/317c: f4 02 00 L2317C pea L20002 & $ffff +02/317f: f4 54 32 pea L23254 & $ffff +02/3182: a2 0c 20 ldx #WriteCString +02/3185: 22 00 00 e1 jsl Toolbox +02/3189: a9 00 00 L23189 lda #$0000 +02/318c: 8d 78 3f sta L23F78 & $ffff +02/318f: a9 03 00 lda #$0003 +02/3192: 8d 7a 3f sta L23F78 & $ffff +2 ++
Worse yet, those STA instruction operands would have been
+shown as hex values or incorrect labels if the DBR had been set incorrectly.
+However, if we have the relocation data, we know the full
+address from which the addresses were formed, and we can tell when
+immediate values are addresses rather than constants. And we can do this
+even without setting the DBR.
+02/317c: f4 02 00 L2317C pea L23254 >> 16 +02/317f: f4 54 32 pea L23254 & $ffff +02/3182: a2 0c 20 ldx #WriteCString +02/3185: 22 00 00 e1 jsl Toolbox +02/3189: a9 00 00 L23189 lda #L30000 & $ffff +02/318c: 8d 78 3f sta L23F78 & $ffff +02/318f: a9 03 00 lda #L30000 >> 16 +02/3192: 8d 7a 3f sta L23F78 & $ffff +2 ++
This feature is still considered "experimental". There are some +issues with it, e.g. the cross-reference table may show an incorrect +offset.
+ +The DEBUG menu is hidden by default in release builds, but can be diff --git a/SourceGen/RuntimeData/Help/editors.html b/SourceGen/RuntimeData/Help/editors.html index f02d514..fe27831 100644 --- a/SourceGen/RuntimeData/Help/editors.html +++ b/SourceGen/RuntimeData/Help/editors.html @@ -305,6 +305,28 @@ not associated with a file offset. If you delete it, you can get it back by using Edit > Edit Header Comment.
+Sets the Data Bank Register (DBR) value for 65816 code. This is used +when matching 16-bit address operands with labels. The new value is +in effect from the line where it's declared to the end of the file, even +across bank boundaries. +If you leave the text field blank, the directive will be removed.
+A hexadecimal value from $00 to $ff can be entered directly. As +with other address inputs, a leading '$' is not required. Entering +"K" will set the DBR to the current address, and will automatically +update if you change the address to a different bank.
+The pop-up menu has a list of all banks that hold code or data. +To make them easier to identify, each is shown with the label on the +first address in the bank, if any.
+While you can override automatically-generated data bank change +directives, you can't remove them individually. You can disable +automatic generation by un-checking "smart PLB handling" in the project +properties.
+Because the directive is frequently associated with PLB
+instructions, double-clicking on a PLB opcode in the
+code list will open the editor.
Notes are similar to long comments, in that they can be arbitrarily long and span multiple lines. However, because they're never included diff --git a/SourceGen/RuntimeData/Help/index.html b/SourceGen/RuntimeData/Help/index.html index 2e0ccb4..d4bfd02 100644 --- a/SourceGen/RuntimeData/Help/index.html +++ b/SourceGen/RuntimeData/Help/index.html @@ -35,6 +35,7 @@ and 65816 code. The official web site is
The 6502 has an 8-bit processor status register ("P") with a bunch of flags in it. Some of the flags determine whether a conditional branch is taken @@ -447,6 +447,35 @@ differently from those outside a project. We refer to these as internal and external addresses, respectively.
+Suppose you have the following code:
++ LDA $1234 + JSR $2345 ++
If we put that in a source file, it will assemble correctly. +However, if those addresses are part of the file, the code may break if +changes are made and things assemble to different addresses. It would +be better to generate code that references labels, e.g.:
++ LDA my_data + JSR nifty_func ++
SourceGen tries to establish labels for address operands automatically. +How this works depends on whether the operand's address is inside the file or +external, and whether there are existing labels at or near the target +address. The details are explored in the next few sections.
+On the 65816 this process is trickier, because addresses are 24 bits
+instead of 16. For a control-transfer instruction like JSR,
+the high 8 bits come from the Program Bank Register (K). For a data-access
+instruction like LDA, the high 8 bits come from the Data
+Bank Register (B). The PBR value is determined by the address in which
+the code is executing, so it's easy to determine. The DBR value can be
+set arbitrarily. Sometimes it's easy to figure out, sometimes it has
+to be specified manually.
Symbols that represent an address inside the file being disassembled @@ -889,6 +918,8 @@ code generator figure out the implementation details.
The relocation dictionaries from the executable are included in the -project file, and can be used to guide the disassembler's analysis. The -"use reloc data" setting in the project properties controls this feature.
+The relocation dictionaries from +the executable are included in the project file, and can be used to guide +the disassembler's analysis. The "use reloc data" setting in the project +properties controls this feature.
A full explanation of the structure of OMF is beyond the scope of this manual. For more information on OMF, see Appendix F of the GS/OS Reference diff --git a/SourceGen/WpfGui/EditDataBank.xaml b/SourceGen/WpfGui/EditDataBank.xaml index daa6b76..683262d 100644 --- a/SourceGen/WpfGui/EditDataBank.xaml +++ b/SourceGen/WpfGui/EditDataBank.xaml @@ -22,7 +22,7 @@ limitations under the License. xmlns:local="clr-namespace:SourceGen.WpfGui" xmlns:system="clr-namespace:System;assembly=mscorlib" mc:Ignorable="d" - Title="Set Data Bank" + Title="Edit Data Bank Register" SizeToContent="WidthAndHeight" ResizeMode="NoResize" ShowInTaskbar="False" WindowStartupLocation="CenterOwner" ContentRendered="Window_ContentRendered">