byuu, do you have a Star Ocean cartridge? Now that you have a working 21FX, the address map for SDD1-with-SRAM really needs to be verified; currently Icarus maps the SRAM in both the "LoROM" fashion (starting at 70:0000) and the "HiROM" fashion (starting at 20:6000 and A0:6000) and somehow I doubt that's correct.
Also, have you tested whether the "LoROM" part of the ROM mapping can be bankswitched on the SDD1 the same way as it can on the SA-1, by setting bit 7 of the ROM bank registers to 1?
(reminder in case you need it: SA-1 bankswitching always affects the HiROM banks. If bit 7 of one of the ROM bank registers is set, the bankswitching also affects the corresponding 1MB LoROM block; if bit 7 is clear then the LoROM blocks are fixed to the first 4MB of the ROM)
Oh, and can you check if SDD1 registers 4802 and 4803 do anything (like enabling/disabling SRAM, or controlling where/how it's mapped)?
Also, have you tested whether the "LoROM" part of the ROM mapping can be bankswitched on the SDD1 the same way as it can on the SA-1, by setting bit 7 of the ROM bank registers to 1?
(reminder in case you need it: SA-1 bankswitching always affects the HiROM banks. If bit 7 of one of the ROM bank registers is set, the bankswitching also affects the corresponding 1MB LoROM block; if bit 7 is clear then the LoROM blocks are fixed to the first 4MB of the ROM)
Oh, and can you check if SDD1 registers 4802 and 4803 do anything (like enabling/disabling SRAM, or controlling where/how it's mapped)?