Advanced Settings
Table of contents
Overview
This page describes board revision 4 (RP2350B) with firmware v4.0.0. Every setting on it applies to this board.
The board comes set up for a stock Amiga 500 or 2000, and most people never change these settings. There are good reasons to try them, though:
- Noisy buses: adjusting the bus timing can fix crashes on a computer whose signals are not clean.
- A degraded clock: adjusting the bus timing can help a computer whose clock has drifted.
- Accelerated computers: an accelerator board changes the bus timing, and the board can be set to keep up.
The CONFIG.TXT file
The settings are in CONFIG.TXT, a plain text file in the ROMEMUL drive you see when you connect the board to your computer.
To change a setting, open the file with a text editor, change the number after its name, save the file and eject the drive. The board reads it when the drive is ejected and uses the new values from the next time the Amiga starts. Lines starting with ; are notes.
This is the file firmware v4.0.0 comes with:
; SidecarTridge cartridge settings
;
; To change a setting, edit the number after its name, save this
; file and eject the ROMEMUL drive. The new settings are used from
; the next time the computer starts. Lines starting with ; are notes.
;
; Some settings only matter on one of the two boards. The file
; INFO.TXT on this drive names yours on its "Board variant" line:
; RP2350A or RP2350B.
;
; --- Timing ---------------------------------------------------------
;
; How long the cartridge waits, after the computer asks for a ROM
; address, before it reads that address. 4 suits most computers. If
; the computer shows a garbled screen, crashes, or does not start
; with a ROM that works elsewhere, try other values, one at a time:
; from 2 to 8 on the RP2350A board (lower values work as 2), from 0
; to 8 on the RP2350B board. Allowed: 0 to 19.
READ_BUS_TICKS = 4
;
; Leave at 0: the Atari ST and the Amiga do not use it.
USE_OE = 0
;
; RP2350B board only; the RP2350A board ignores these three. Each
; one makes the cartridge answer the computer a little sooner.
; Leave them at 1. Set one to 0 only to troubleshoot a computer that
; does not start. Allowed: 0 or 1.
CE_SYNC_BYPASS = 1
WRITE_ON_DRIVE = 1
DMA_HIGH_PRIORITY = 1
;
; --- Rescue ROM without the RESCUE switch --------------------------
;
; Seconds. To start the rescue ROM (named in RESCUE.TXT; normally
; the ROM switcher) without the RESCUE switch, switch the computer
; on with its RESET button held down, keep holding it for longer
; than this many seconds, then release it. A normal start is not
; delayed. 0 turns this off. Allowed: 0 to 600.
RESCUE_TIMEOUT = 0
;
; --- Speed ----------------------------------------------------------
;
; RP2350B board only: 1 allows ROMs larger than 512 KB, up to 1 MB.
; While such a ROM runs, the cartridge works at its highest speed,
; faster than its chip is rated for. With 0, a larger ROM is refused
; and the rescue ROM starts instead. The RP2350A board never runs
; ROMs larger than 512 KB, and a rescue ROM is never larger than
; 512 KB on either board. Allowed: 0 or 1.
LARGE_ROMS = 0
;
; 1 if the computer has an accelerator board or a faster bus and its
; ROMs crash or do not start: the cartridge then always works at its
; highest speed, faster than its chip is rated for. Both boards.
; Allowed: 0 or 1.
ACCELERATED_BUS = 0
To see the values the board is using, press C in the SWITCHER, or run the self-test of the rescue switcher: its Configuration line lists them.
READ_BUS_TICKS
How long the board waits, after the Amiga asks for a ROM address, before it reads that address. The default, 4, suits most computers.
If your Amiga shows a garbled screen, crashes, or does not start with a ROM image that works elsewhere, try other values, one at a time: from 0 to 8. A computer with a noisy bus may need 6 or 8; one with an accelerator that shortens the bus cycle may work better with 2 or lower.
Allowed: 0 to 19.
In our experience with accelerator boards, the board does not work on anything faster than 20-24 MHz, with firmware v3.x and v4.x alike, but we encourage you to experiment. Many other things affect the stability of an accelerated computer: the power supply, the RAM and the rest of the system. Use it at your own risk, and share your findings with the community.
USE_OE
Leave it at 0. It tells the board to wait for the ROM’s Output Enable signal before answering, which the Atari ST and the Amiga do not need: on the TOS and Kickstart carrier boards that signal is always active.
CE_SYNC_BYPASS, WRITE_ON_DRIVE and DMA_HIGH_PRIORITY
Each one makes the board answer the Amiga’s ROM reads a few nanoseconds sooner. Leave all three at 1, the default.
CE_SYNC_BYPASS: the board reads the Amiga’s chip-enable signal directly, without the two-step input synchroniser of its microcontroller, so it notices a ROM read about 8 ns sooner.WRITE_ON_DRIVE: the board opens its data bus buffer in the same step that puts the data on the pins, about 4 ns sooner.DMA_HIGH_PRIORITY: inside the microcontroller, the copy that fetches each ROM word goes before any other memory traffic.
Setting one to 0 trades those few nanoseconds for a more conservative timing. Do it only to troubleshoot an Amiga that does not start: change one at a time, put it back to 1 if it makes no difference, and try these before READ_BUS_TICKS. Allowed: 0 or 1.
RESCUE_TIMEOUT
For computers with a RESET button, such as the Atari ST: switched on with RESET held for longer than the seconds set here, they start the rescue image when RESET is released.
It does not work on the Amiga 500 and 2000, which have no RESET button. Leave it at 0, and use the RESCUE button to start the rescue image.
0 turns it off, and is the default. Allowed: 0 to 600.
ACCELERATED_BUS
Set it to 1 if your Amiga has an accelerator board or a faster bus, and its Kickstart crashes or does not start. The board then always runs at its highest speed, which is faster than its chip is rated for: use it only if you need it.
0 is the default: the board runs at its normal speed.
LARGE_ROMS
1 allows Kickstart images larger than 512 KB, up to 1 MB. This is experimental. It can be tested on an Amiga 500+ or 600, whose carrier connects the upper half of a 1 MB ROM. While such an image runs, the board works at its highest speed, which is faster than its chip is rated for.
A 1 MB image holds the $E00000 half first and the $F80000 half second: the reverse of the merged ROM that Kickstart builders make for burning a 27C800. Name the image in DEFAULT.TXT: an image chosen in the SWITCHER or the rescue switcher runs with whatever upper half the board last stored, until the board is next connected to a computer over USB.
0 is the default: an image larger than 512 KB is refused, and the board starts the rescue image instead. An image above 1 MB is always refused. The rescue image itself is never larger than 512 KB.
Large ROMs explains the feature step by step: which Amigas, how to prepare a 1 MB image and how to start it.
As a kind reminder, ALWAYS eject the ROMEMUL drive after changing anything on it. This makes sure the changes are saved and the board uses them.