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Question inspired by this answer's last paragraph: https://retrocomputing.stackexchange.com/a/1307/2155
The Revision 1 A1200 schematics show that the system originally had support for a two internal 8bit x 256K Flash memory chips (for a total of 512KB), selected by a combination of the /FLASH and other signals coming from Gayle.
Back in the days I never heard of this detail. What was this memory for?
Bonus question: how much ROM can a Gayle-based system actually address?
An hypotesis can be made by reading Gayle's original datasheet (you can find it linked here).
3.0 FLASH ROM There is provision for an optional flash ROM device. The intent is that this is a possible replacement for a floppy disk drive in an extremely low end variant of the A300. The enable for the flash rom is called -FLASH-CE, and is active in the address range from $0xA00000 to $0xA7FFFF. This output is enabled when the proper data strobe is asserted, and the address is in range.
(3.0 in the first line is the chapter number, not a reference to AmigaOS 3.0)
Later the memory map confirms that and also shows a 1MB Workbench ROM area:
0xA00000 to 0xA7FFFF 512KB Flash ROM
0xA80000 to 0xB7FFFF 1MB System ROM selected (optional workbench ROM)
About the 1MB System ROM area, the datasheet says:
2.0 SYSTEM ROM The onboard ROMs are selected in the address range from 0xA80000 to 0xB7FFFF, 0xE00000 to 0xE7FFFF, and 0xF80000 to 0xFFFFFF. The ROMs are also selected in the range from 0x000000 to 0x1FFFFF when the internal overlay signal (OVL) is high (this allows the RESET vectors to be contained in the ROMs). The internal OVL signal becomes asserted at reset, and negates on the first write to CIA1 (address range of 0xBFD000 to 0xBFDFFF.
Note that the total addressable ROM space described above is 2MB; we know from Richard Downer's excellent answer that the 512KB extended CD32 ROMs appear at 0xE00000 to 0xE7FFFF. Subtracting the standard 512KB Kickstart area, this leaves exactly 1MB usable to address another 1MB of ROMs.
This is in addition to the Flash RAM from 0xA00000 to 0xA7FFFF.
As per software support, it should be noted that the leaked AmigaOS 3.1+ source code sports a ROM Disk DOS handler (DOS name ROM:) in the /os-source/v40_src/kickstart/romdisk directory, that appears to be a copy of the standard RAM Disk DOS handler with write support disabled with data coming from a disk image created with the included makeromimage command line utility.
So by Gayle's datasheet and the R1 schematics, it looks like the idea could have been to both put Workbench resident modules in the additional 1MB ROM (Kickstart 3.1 scans the 0xA80000 - 0xB7FFFF area too) and also have a 512KB Flash RAM area for the user to add additional resident modules in LIBS: and DEVS: and configuration files (by means of the 2.0+ multi-target ASSIGN feature, and the ROM disk?).
Note that the Gayle datasheet describes a prerelease version, so things may have changed in the true chip. Indeed, in the R2 A1200 schematics, the Flash RAM is 1MB, which would have provided for space to keep a whole rewritable minimal Workbench installation (a far better idea). It would be nice to try if the existing Gayle can drive the /FLASH line and for what addresses.
So it looks like the idea was not for the Flash RAM to be used to store an upgradable Kickstart (the most sensible choice of all, although handling an incorrectly programmed Flash Kickstart would have been tricky).
My guess would be that it was intended to offer upgradeable ROM modules for future peripherals or software.
@user180940's answer links to the Gayle datasheet that mentions the flash memory was intended as a replacement for the floppy drive in a low cost A300 machine. What would an Amiga without a floppy drive look like? Well, there is the CD32, which has a CD-ROM drive for storage and all the necessary software for it in the ROM.
The original idea with the A600, which was at first called the A300, was a low cost machine that consumers could upgrade over time. Having a flash ROM would allow the ROM to be upgraded to support things like CD-ROMs or even add/upgrade built-in software like games or productivity apps.
Quite how such an update would have been loaded is unclear though as without a floppy drive or CD-ROM as standard there is no way to get data on to the machine. Perhaps it could have been offered as a dealer upgrade using an external floppy drive.
One other possibility is that it could have been intended as a read-only memory in the A300 itself, but removable and upgradeable by dealers when selling upgrades to the machine. The more complex upgrades would be fitted by the dealer, who would use a programmer to upgrade the flash ROM at the same time. It's not clear if the A300 itself would have had any write capability for the flash memory.
