TinyEhci

TinyEHCI

Tiny, less than 512 bytes, bare metal EHCI read step5_gh/bootsector.asm is its entry point

Explanation

Tricks to help reduce them:

1. place GTD in BPB;
2. place SCSI CBW in BPB;
3. place StandardUsbRequest in BPB.
4. replace call/ret by inline
5. manual size optimization
6. using data created by BIOS after loading bootsector
7. watch every register

Full search process to find only a specific memory card in the USB2 slot. Pseoudocode:

enumerate pci to find usb/MSD {
	enumerate usb, to find EHCI {
		if ( read from usb, to detect flashstick ) {
			if ( read flashstick to find true signature )
				jump to first readed byte
		}
	}
}

Transcription:

• Enter to bigUnrealMode
• Iteration loop in PCI
• …
• Using BIOS USB data to preparing transports
• …
• Command to read descriptor and find Endp “id”
• …
• Read usbstick from “second sector”
• …
• Compare signature from usbstick
• …
• Diagnostic messages

Write bootsector in usbstick

If want to write bootsector in usbstick … TODO: HxD screens or gif …

Example

Example qemu output … TODO: replay asciinema …

Requirements

Hadrware with:

• BIOS with “USB Legacy” boot switching capability
• Compatible Intel x86 processor with 32-bit addressing support
• USB2.0 connector “on” the PCI bus
• …

a link to repo