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Johan Vromans
Articles » TM4001WLMi » ACPI Hacking » DSDT

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DSDT is an acronym for Differentiated System Description Table. This table contains the Differentiated Definition Block, which supplies the information and configuration information about the base system. It is always inserted into the ACPI Namespace by the OS at boot time.

Unfortunately, many hardware vendors and OEMs are not capable of supplying fully functional tables, and this system is no exception.

Using the method and tools described here I extracted my DSDT and applied the necessary fixes. Quite surprising, I had to change the maximum frequency the CPU can operate on from 1.6GHz to 1.5GHz. No, it didn't actually run at 1.6GHz, it was just confusing.

Update: Careful inspection learned that the CPU was using speed frequencies 1.5GHz, 1.2GHz, 1GHz, 800MHz and 600MHz. The speeds reported by the DSDT were 1.5GHz, 1.4GHz, 1.2GHz, 800MHz and 600MHz. So I had to correct these as well.

According to the people on the acpi-devel mailing list, mistakes like this are common.

You can find my original DSDT here, and the fixed version here.

To get the modified DSDT into operation, I applied the DSDT in INITRD kernel patch. This makes it possible to add the modified DSDT to the initrd where it will be picked up automatically upon boot.

Later I started using Matthias Hensler's prebuilt 'cubbi' kernels for TuxOnIce. They all have the DSDT in initrd feature built-in.

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articles/TM4001WLMi/acpi/dsdt.html last modified 11:31:40 26-Dec-2007