mirror of
https://github.com/86Box/docs.git
synced 2026-02-21 17:15:33 -07:00
71 lines
3.6 KiB
ReStructuredText
71 lines
3.6 KiB
ReStructuredText
ISABugger
|
|
=========
|
|
|
|
The ISABugger card provides a debugging interface for software developers, consisting of two 8-bit hexadecimal displays and two banks of 8 LEDs, all controlled by the emulated machine. It can be enabled through the :ref:`Peripherals settings page <settings/peripherals:ISABugger>`.
|
|
|
|
These displays and LEDs are displayed in the :ref:`status bar <usage/statusbar:ISABugger>` as described in the diagram below:
|
|
|
|
.. image:: images/isabugger.png
|
|
:align: center
|
|
|
|
Background
|
|
----------
|
|
|
|
From ``src/device/bugger.c``:
|
|
|
|
.. code-block:: none
|
|
|
|
Implementation of the ISA Bus (de)Bugger expansion card
|
|
sold as a DIY kit in the late 1980's in The Netherlands.
|
|
This card was a assemble-yourself 8bit ISA addon card for
|
|
PC and AT systems that had several tools to aid in low-
|
|
level debugging (mostly for faulty BIOSes, bootloaders
|
|
and system kernels...)
|
|
|
|
The standard version had a total of 16 LEDs (8 RED, plus
|
|
8 GREEN), two 7-segment displays and one 8-position DIP
|
|
switch block on board for use as debugging tools.
|
|
|
|
The "Plus" version, added an extra 2 7-segment displays,
|
|
as well as a very simple RS-232 serial interface that
|
|
could be used as a mini-console terminal.
|
|
|
|
Registers
|
|
---------
|
|
|
|
The ISABugger's control registers can be accessed through the following operations on I/O ports ``0x7a`` and ``0x7b``:
|
|
|
|
* **Writing:** write the register's index to port ``0x7a``, then write the value to port ``0x7b``.
|
|
* **Reading:** write the register's index to port ``0x7a``, then read the value from port ``0x7b``.
|
|
* **Index reading:** the last register index written to port ``0x7a`` can be read back from the same port. The most significant bit is always set, as an indicator that the ISABugger is enabled.
|
|
|
|
.. note:: The ISABugger I/O ports only support byte (``inb``/``outb``) operations. Word (``inw``/``outw``) and dword (``inl``/``outl``) operations will result in undefined behavior; so will selecting or attempting to read back an unknown register index, or performing an illegal operation such as reading from a write-only register.
|
|
|
|
Register reference
|
|
^^^^^^^^^^^^^^^^^^
|
|
|
|
.. rubric:: Index ``0x00`` - Red LEDs (write-only)
|
|
.. rubric:: Index ``0x01`` - Green LEDs (write-only)
|
|
|
|
Each LED bank shows a binary representation of the 8-bit value written to its register, from the most significant bit on the left to the least significant bit on the right. Setting a bit will light up its corresponding LED (displayed as **G** or **R**), and clearing a bit will dim its LED (displayed as **g** or **r**).
|
|
|
|
.. rubric:: Index ``0x02`` - Right display (write-only)
|
|
.. rubric:: Index ``0x04`` - Left display (write-only)
|
|
|
|
Each display shows a hexadecimal representation of the 8-bit value written to its register.
|
|
|
|
.. rubric:: Index ``0x20`` - Serial port data (not implemented) (read/write)
|
|
.. rubric:: Index ``0x40`` - Serial port configuration (not implemented) (read/write)
|
|
|
|
While the aforementioned real ISABugger card is equipped with an independent RS-232 serial interface, that feature is currently not implemented on 86Box in an user-facing manner.
|
|
|
|
.. rubric:: Index ``0x80`` - Initialize (not implemented) (write-only)
|
|
|
|
This register has **no effect** on 86Box, as the emulated ISABugger is always enabled and ready.
|
|
|
|
.. rubric:: Index ``0xff`` - Reset (special)
|
|
|
|
Writing register index ``0xff`` to port ``0x7a`` will immediately reset all registers to their startup value, clearing all displays and LED banks.
|
|
|
|
This is a **special register** which cannot be read or written; writing to port ``0x7b`` immediately after a reset will result in the value being sent to the default register index of ``0x00``, which corresponds to the red LEDs.
|