When SeaBIOS attempts to boot from disk drive, it does not time out after unsuccessful boot. The drive in the MacBook2,1 laptop I have is corrupt and loops infinitely trying to boot from it; not moving on to the next media device. Please provide a time-out/error-out from a certain case.
In order to troubleshoot this to flash another BIOS via command-line, I will remove the HDD in posterity.
I'm curious, I don't know whether the HDD on a macbook21 is ATA/IDE or whether it's AHCI/SATA
Can you flash the GRUB ROM and type ls into the GRUB terminal? I ask because I've never taken apart a macbook21 before.
If it's IDE, there's one thing I can possibly think of. In SeaBIOS, the default mode for IDE is PIO mode, but you can enable DMA mode. I disable PIO mode in this release, and enable DMA mode instead, but maybe that was a mistake. It's possible that this isn't the cause. Though if you tell me the HDD is IDE, not SATA, I will send you a ROM with SeaBIOS set to PIO mode and you can try that.
The reason I set DMA mode is because of GA-G41M-ES2L where PIO mode is extremely slow in SeaBIOS.
(memdisk) (proc) (cbfsdisk) (ahci0,gpt3) (ahci0,gpt2) (ahci0,gpt1) (ata0)