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Re: 65c02 disassembler on IIe
Michael Spangler wrote:
> Also, does anyone know if an image of the legendary IIe debug ROM
> exists anywhere on the internet?
I have it. Instructions are below. E-mail me if you want the binary
file. This is the ROM version I use in Apple II emulators as well as my
65802-equipped Apple IIe.
--
Paul R. Santa-Maria
Monroe, Michigan USA
Apple // Extended Debugging Monitor
Introduction:
The Extended Debugging Monitor (EDM) is a superset of the standard Apple
//e monitor with which can access all of the 128K of main and auxiliary
memory. It is made available on a set of modified Apple //e ROMs.
The standard ROM monitor was designed to really only support 48K of
memory in an Apple //. With the addition of both the language card and
now the extended 80-column card, it is now necessary to have a new
monitor that can access all of the memory available in an Apple //.
In addition to providing access to the full 128K //e memory, the monitor
features a "RESUME" command to resume operation in a non-standard memory
environment and an improved memory location display format.
In implementing EDM, the diagnostics and cassette support have been
removed and the debugging monitor extensively revised. However, as the
remaining firmware remains untouched, applications which run on the
revised //e ROMs should run on the EDM ROM.
Description:
The EDM is a superset of the old monitor. Commands in the previous
monitor format produce very similar results. Commands like SEARCH and
ASSEMBLE and the as ASCII input modes added in the //e ROM revision are
still available. The address xxxx refers to memory location xxxx under
the current memory mapping configuration. If the memory configuration
is changed by hitting soft switches like RDCARDRAM, ALTZP, xxxx may
change its meaning accordingly. This is still true in the EDM, although
hitting memory softswitches from the monitor is now neither necessary
nor recommended since more direct techniques for getting to the various
parts of memory are provided.
The internal-ROM/slot-ROM softswitch has no effect in the EDM.
Examination of the internal ROM is not permitted from the EDM since the
internal ROM contains routines internal to the firmware and need not be
directly accessed by the user. This should not be a major handicap.
Using the old commands results in some differences. Memory display is
16 bytes per row when the screen width allows it, and both the
hexadecimal and ASCII values are shown. In ASCII display, the high bit
is ignored and unprintable characters are replaced by "." so output can
be sent to printers. Because memory locations will be read twice during
the display, some soft switches affected by multiple accesses may be
affected differently by the new monitor.
EDM has a 65C02 disassembler and mini-assembler, but EDM itself does not
use any 65C02 instructions and hence may run on machines with either an
NMOS 6502 or a 65C02.
A new address syntax is used to specify all memory. Addresses are
represented by b/xxxx. b, a bank number, is either 0 or 1. (For b > 1,
even values are treated as 0, odd values as 1.) Bank 0 is the RAM
memory on the main logic board and bank 1 is the AUX memory on the 80
column card. This convention applies for main or AUX Memory in the
ranges $0000-$BFFF and SE000-$FFFF. There is a different convention for
the bank switched memory and I/O areas ($C000-$DFFF).
ADDRESS SYNTAX:
0/nnnn = address nnnn in MAIN memory
1/nnnn = address nnnn in AUX memory
where nnnn is in the range $0000 - $BFFF or $E000 - $FFFF
There is no system RAM in the address range $C000 to $CFFF. ROM
residing there could be accessed by $Cxxx. Taking advantage of this
opportunity, a different meaning is assigned to b/Cxxx. b/Cxxx refers
to the main/aux language card bank 1 address $Dxxx, while b/Dxxx refers
to the main/aux language card bank 2 address $Dxxx. Using these
notations we can refer to all RAM and all ROM except the internal ROM.
This notation can be used in commands like EXAMINE, STORE, MOVE, VERIFY,
SEARCH, DISASSEMBLE and even ASSEMBLE. The only exception is the bank
is ignored in the GO command.
ADDRESS SYNTAX;
0/Cnnn = address SDnnn in MAIN language card bank 1
0/Dnnn = address $Dnnn in MAIN language card bank 2
1/Cnnn = address $Dnnn in AUX language card bank 1
1/Dnnn = address $Dnnn in AUX language card bank 2
When an address range is specified as in {adrs1}.{adrs2}, the second
address should not have a bank number. If one is present, it is
ignored. In the mini-assembler, a bank number may be specified in the
beginning address, but you cannot put a bank number in the middle of an
instruction. BNE 1/300 is treated as an error.
The GO command in EDM docs not use a bank number in the address. The
syntax is exactly the same as in the standard monitor. If your program
is running in a non-standard memory configuration, you cannot simply use
the GO command to resume execution. In such a case, you must set up the
correct memory state first. Whenever a BRK or an interrupt occurs, EDM
handles it just as the //e revision ROM's handle it, except that EDM
will correctly handle a BRK in the alternate Zero Page. For an
interrupt or BRK, the firmware sets the machine back to the standard
memory configuration and encodes the memory state in a byte located at
$64. The GO command leaves the return address on the stack, which means
that an RTS instruction will cause a return to the monitor.
In order to allow the correct resumption of execution after an interrupt
or BRK, EDM has added a RESUME command. The syntax is nnnn^R (^R =
control-R), where nnnn is the address at which to resume execution.
Note, this address does not use a bank number. The RESUME command will
use the memory state value stored in location $44 to setup the correct
memory state before beginning execution. You can modify this value in
order to begin execution in any memory configuration. The RESUME
command leaves nothing on the stack and is, therefore, a true resume
operation. You can think of a BRK-RESUME combination as an interrupt
that occurs at a specified point in your program that allows you to
examine and modify memory during the "interrupt".
For both the GO and the RESUME commands if nnnn is not specified, the
address stored at locations $3A and $3B is used.
The memory state value at location $44 is displayed as register M in the
register display (using the ^E command). The interpretation of the bits
in register M is shown below:
bit 7 = 1 if auxiliary zero-page/stack switched in
bit 6 = 1 if 80STORE and PAGE2 both on
bit 5 = 1 if auxiliary RAM switched in for reading
bit 4 = 1 if auxiliary RAM switched in for writing
bit 3 = 1 if bank-switched RAM being read
bit 2 = 1 if bank-switched $D000 page 1 switched in
bit 1 = 1 if bank-switched $D000 page 2 switched in
bit 0 = 1 if internal CX ROM switched in
In the standard monitor location $40-$41 is set to $45, providing a
short-cut for modifying the pseudo-accumulator at location $45. EDM now
sets this location to $44 so that modifications of this type can begin
with register M.
If you want to run any program using the alternate zero page, and if you
plan to use either interrupt or BRK, you must follow the stack pointer
convention used by the firmware. Normally, the top of the stack when a
BRK occurs is located at the "stack-register S" + 5. If a BRK occurs
when the alternate zero-page/stack is used, the value in "stack-register
S" is invalid. To find the top-of-stack of the alternate stack, look at
location $101 in the alternate stack and add 1 to that value.
Since diagnostics have been removed, SOLID-APPLE CONTROL RESET will not
bring up the diagnostics. Instead, this will cause a direct jump into
EDM without trashing any memory. This can be very useful for debugging.
Details on difference between EDM and the //e revision ROM :
EDM uses some extra memory locations. They are located in slot 3 screen
holes and slot 0 screen holes. Some of these are temporary locations
already used by the firmware, so they should not conflict with any
program. The slot 3 screen holes used are:
$6FB - contains the bank number (normally used by PASCAL only)
$7FB - contains the bank number during MOVE/VERIFY
$67B - normally used by video firmware
$77B - normally used by PASCAL or video firmware
The slot 0 screen holes are:
$6F8, $778 - modified by EDM if alternative zero page is accessed.
Entry points $FECD and $FEFD for cassette I/O are now dummy routines
Entry points VERIFY ($FE36) and LT ($FE5E) no longer exist.
Entry points INSTDSP ($F8D0) and LIST ($FE5E) still disassemble 1 or 20
instructions, but unless the bank register location $6FB is set up
properly, you may disassemble the wrong bank. Valid bank values are $80
(no bank), $00 (bank 0) and $01 (bank 1).
In the old monitor, commands of the format xxxx<yyyy.zzzzC would copy
locations $3E-3F to $44-45. This does not seem to serve any useful
purpose and destroys machine state value in $44-45, therefore EDH no
longer does this.
Because EDM recognizes 65C02 opcodes, you must be careful to ignore any
65C02 instructions that may be displayed by the disassembler when the
code does not actually contain these instructions.
The ID byte at $FBC0 contains $E1 to identity the EDM ROM.
EDH is identified at boot time by the display of "Apple ][DB", where the
"DB" stands for "Debugging".