emu48-mirror/DEBUGGER.TXT

Debugger in Emu48/Tools/Debugger...
-----------------------------------

This is a short description of the internal assembly debugger of Emu48. The debugger is not perfect and/or complete. I provide it as it is. Please don't send me any suggestions or changes at the moment. If you have a better idea make it for yourself. Of course you're free to publish them or send me your changes.

The debugger was designed to help customers inspecting assembler code objects, a part that cannot be handled satisfactorily by the JAZZ package. Thanks to Mika Heiskanen and all the others supporting this great program.

After starting the debugger the emulation will stop at the current PC position. The emulation will continue after closing the debugger window. Please remember that the clock now shows the wrong time.


1.) Menu Debug

- Run F5

Continue calculator emulation under debugger control. The emulation will stop at a breakpoint. Please remember that the emulation speed is slower than without debugger control.

- Run to Cursor F6

Execute program until address at cursor position is reached. Code and memory breakpoints are still active and may stop execution before.

- Step Into F7

Execute one code instruction.

- Step Over F8

Execute a GOSUB, GOSUBL or GOSBVL as one instruction. Normally the instruction cursor will set to the position behind the GOSUB instruction.

But this makes trouble in the following code part:

	GOSUB	+
	NIBASC	/Hello world/
+	C=RSTK

The program counter will never reach the address behind the GOSUB instruction. The debugger solve this problem by breaking the emulation when the stack has the same level before the GOSUB instruction. In this example the single step execution will continue after the C=RSTK instruction.

- Step Out F9

Continue the program until a RTI, RTN, RTNC, RTNCC, RTNNC, RTNSC, RTNSXN, RTNYES instruction is found above the current stack level.

At some code constructions (mostly used to save space on the hardware stack) like

	C=RSTK
	PC=C

and

	C=RSTK
	RSTK=C
	RTN

the stop address will be wrong. The problem in both code fragments is the C=RSTK opcode. In the first example there is no RTN instruction to stop. In the second one the C=RSTK instruction purge the original return address and then the RSTK=C instruction is interpreted as a GOSUB instruction.

In opposite the following code will work fine:

	RSTK=C
	..
	code		<- F9 was pressed here
	..
	GOSUB	-
	C=RSTK
	RTN		<- emulation will stop after this instruction
-	RTN

So be careful using the F9 key.

- Break F11

Stop the emulation at the current program counter position.


2.) Menu Breakpoints

- Set Breakpoint F2

Toggle a code breakpoint at the cursor position in the code window.

- Edit Breakpoints...

You get a sorted list of the current code and memory breakpoints. When the breakpoint is checked it's enabled otherwise it's disabled. With "Add" you can add a new or enable an existing breakpoint, with "Delete" you can delete the selected ones. Addresses greater than #FFFFF are cut after the fifths nibble. When adding a new breakpoint, you must select if this is a "Code", "RPL", "Memory Access", "Memory Read" or "Memory Write" breakpoint.

  - "Code" stop before opcode execution on this address
  - "RPL" stop on the first opcode of the selected RPL address
  - "Memory Access" stop before reading or writing to the selected address
  - "Memory Read" stop before reading the selected address
  - "Memory Write" stop before writing to the selected address

With a left mouse button double click on a breakpoint you can toggle the check box inside.

- Clear All Breakpoints

Clear all breakpoints except the NOP3 ones.

- NOP3 Code Breakpoints

What are NOP3 code breakpoints? As you know user programs are loaded somewhere in memory and can be moved after a garbage collection. So it's very difficult to break a user program at a hard set breakpoint with F2. To solve this problem the debugger will stop emulation at a NOP3 opcode. So you can easily add a NOP3 command into your sources to force a break condition. To enable this you have to check this item.

NOP3 and NOP3, what's the difference? The Saturn CPU has no NOP command, so NOP3 is an opcode that is three nibbles long and doesn't change a register. In the HP SASM.DOC document two different opcodes are defined for NOP3:

  Opcode 820 for HST=0 0

and

  Opcode 420 for GOC + (next line)

In the assembler of the HPTOOLS 3.x package NOP3 is defined as opcode 820. The advantage of the opcode is that the execution time is always the same, independent from the carry flag. This code is used in the HP48 ROM as well. So I decided to use the GOC opcode for a code breakpoint condition.

A short example:

ASSEMBLE
  NIBASC /HPHP48-E/

BREAK	MACRO
	CON(3)	#024		NOP3
	ENDM

RPL
CODE
	BREAK			code breakpoint

	GOSBVL	=SAVPTR		save register

	GOSUB	+		problem for step over
	NIBASC	/Hello world/
+	C=RSTK

	GOVLNG	=GETPTRLOOP
ENDCODE

- CODE Object Breakpoints

If this item is checked, the debugger stops program execution at the first instruction of every DOCODE object which isn't located in ROM. For inspecting DOCODE objects in ROM use the static CODE breakpoints instead please.

- RPL Breakpoints

If this item is checked, the debugger stops program execution on every instruction called after a PC=(A) or PC=(C) opcode. This is normally the begin of a new RPL command. RPL breakpoints use a "-R" marker instead of the assembler "->" PC position marker.


3.) Menu Interrupts

- Step Over Interrupts

If this item is checked, interrupt handler code will be skipped. This option is useful when you don't want to debug the interrupt handler. But be careful, when you disable the interrupts all code until interrupt enable belong to the interrupt handler code and couldn't executed in single step any more. Code and memory breakpoints are still active.

You can also use this option if you want to quit the interrupt handler. Just check this option, press F7 for "Step Into" for stopping the debugger behind the RTI instruction, and uncheck this option again.


4.) Menu Info

- Last Instructions...

This is a short viewer for the last 255 executed CPU addresses. The disassembled opcode maybe wrong, because only the CPU address of each command was saved and memory mapping may have changed meanwhile. In the "Last Instructions" dialog you can copy selected lines to the clipboard or clear this list.


5.) Code window

This windows shows you the disassembled code. The line with the current PC is marked with a "->" between the address and the disassembly.

You can use the UP, PAGE UP, DOWN and PAGE DOWN keys to scroll the window content. There is one strange behavior, when you move to higher addresses the debugger is able to disassemble the next line correctly, but when you move to cursor to lower addresses the debugger does not know if this address is at the begin or inside of an opcode. In result you get wrong disassembled lines.

Context menu pressing the right mouse button:

- Go to address... G

Moves the cursor to the specified code address.

- Go to PC

Sets the cursor to the actual position of the PC.

- Set breakpoint F2

Toggle a code breakpoint at the cursor position in the code window.

- Set PC to selection

Set the PC to the cursor position. Be careful with this command, you change the execution order of the commands!


6.) Register window

Here you can see the actual contents of the CPU registers. The values are only updated at a program execution stop. All changed CPU registers are highlighted.

With the left mouse button you change the content of the register. On bit registers, like CY and Mode, the state change immediately without any request.


7.) Memory window

This windows shows the memory content.

You can use the arrow, PAGE UP and PAGE DOWN keys to move the cursor to a memory position. With a double click on the left mouse button you change the content of the two addresses. When the memory position is read only (ROM) the content wouldn't change.

Context menu pressing the right mouse button:

- Go to address... G

Moves the cursor to the specified memory address.

- Go to PC

Sets the cursor to the actual position of the PC.

- Go to D0

Sets the cursor to the actual position of the D0 register.

- Go to D1

Sets the cursor to the actual position of the D1 register.

- Go to Stack

Sets the cursor to the return address placed in the top level of the stack.

- Find... F

Calls the "Find" dialog box, allowing you to search for a data sequence in hexadecimal or ASCII mode. The search area is restricted to the mapped CPU address area, so it isn't possible to access hidden memory. When you close the "Find" dialog box, you will loose all saved strings in the data combo box.


8.) Stack window

The content of the hardware stack is viewed here. In "1:" is the current return address. A double click on an item shows the address content in the code window.


9.) MMU window

The configuration of the memory controllers is viewed here. The viewed addresses are the first configured addresses of the modules and may differ from the given address in the CONFIG command.

This example

	LC(5)	#C0000		128KB size
	CONFIG
	LC(5)	#98765		start address of module
	CONFIG

will config a 128KB module at address #80000 and not at the given address. So the MMU viewer will show you address #80000.


10.) Miscellaneous window

The Miscellaneous window show you the internal state of the interrupt flag, the 1ms keyboard handler and the contents of the Bank Switcher latch. The Bank Switcher item is only enabled on calculators with a latch inside. You see the loaded value of the address lines A6-A0. You have to ignore the last bit (A0), because it isn't wired to the six bit latch.

You can change the values by pressing the left mouse button over the old content.


05/15/01 (c) by Christoph Gie<69>elink, cgiess@swol.de