Wednesday, 5 March 2014

Buggy USB support in BIOSes

Most BIOSes can boot from a USB drive these days, but they don't always work well.

For instance, my Asus EeepC 904HA netbook has buggy USB boot code in the BIOS. If I boot to Easy2Boot from my 2TB USB hard disk, when CheckAccess.g4b runs (which checks access to the end of the last partition on the USB boot drive), it reports loads of read errors. This is because the USB code in the BIOS cannot access any sector past 137GB on the USB drive (although the BIOS can access all sectors on the internal hard disk).

For another example of buggy USB BIOS support, see here. In this case Leolo had a system with an AsRock P4i65G board which would not boot successfully to WinPE (Win7 install) from a USB drive - but only the AsRock system - all other systems booted fine.

In the past, one way of getting around this type of buggy BIOS was to use Plop! This loads it's own USB USB 2.0 driver and so does not use the BIOS USB driver. The problem with Plop! is that the driver is read-only. This is OK for primitive booting but not for boot managers which need read/write access to the USB drive (such as Easy2Boot).

In both these cases, using the new grub4dos v0.4.6a  fixes the problem. This version of grub4dos contains a USB 2.0 driver but it is not active by default. You need to issue a command to initialise the USB driver:
      usb --init

The USB driver in grub4dos 0.4.6a still has a few bugs, but the latest (developer) version is looking much better.

When it is robust enough, I will add it in to Easy2Boot. If the CheckAccess.g4b fails, E2B will ask if you want to switch to v0.4.6a. There will also be a variable in the MyE2B.cfg file to use the new version and USB driver, as well as a new Main menu entry (determined by a .mnu file which you can remove if you don't want it).

If you have a system with a 'bad' BIOS that boots to Easy2Boot but no further, you can try the new version with Easy2Boot as follows:

1. Extract the grldr file from here (this is a new, developer test version 5th March 2014 - check here for a later version) and overwrite the grldr file in the root of your E2B drive.

2. Edit the \menu.lst file in the root of the E2B drive and add
usb --init
as the first line, or try 
set /p ask=Use grub4dos USB driver (Y/N) : 
if /i "%ask%"=="Y" usb --init
if you want the option to install the USB drivers.

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