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Alex Hung
on 8 July 2019

Analyze ACPI Tables in a Text File with FWTS

I often need to implement tests for new ACPI tables before they become available on real hardware. Fortunately, FWTS provides a framework to read ACPI tables’ binary.

The below technique is especially convenient for ACPI firmware and OS kernel developers. It provides a simple approach to verifying ACPI tables without compiling firmware and deploying it to hardware.

Using acpidump.log as an input for FWTS

The command to read ACPI tables’ binary is

# check ACPI methods in a text file
$ fwts method --dumpfile=acpidump.log


# check ACPI FACP table in a text file
$ fwts facp --dumpfile=acpidump.log

where acpidump.log contains ACPI tables’ binary in a specific format as depicted below:

  • Table Signature – the 4-byte long ACPI table signature
  • Offset – data starts from 0000 and increases by 16 bytes per line
  • Hex Data- each line has 16 hex integers of the compiled ACPI table
  • ASCII Data – the ASCII presentation of the hex data

This format may look familiar because it is not specific to FWTS. In fact, it is the same format generated by acpidump. In other words, the below two code snippets generate identical results.

# reading ACPI tables from memory
$ sudo fwts method
# dumping ACPI tables and testing it
$ sudo acpidump > acpidump.log
$ fwts method --dumpfile=acpidump.log

For developers, using –dumpfile option means that it is possible to test ACPI tables before deploying them on real hardware. The following sections present how to prepare a customized log file.

Using a customized acpidump.log for FWTS

We can use acpica-tools to generate an acpidump.log. The following is an example of building a customized acpidump.log to test the fwts method command.

Generate a dummy FADT

A Fixed ACPI Description Table (FADT) contains vital information to ACPI OS such as the base addresses for hardware registers. As a result, FWTS requires a FADT in an acpidump.log so it can recognize acpidump.log as a valid input file.

$ iasl -T FACP
$ iasl facp.asl > /dev/zero
$ echo "FACP @ 0x0000000000000000" >> acpidump.log
$ xxd -c 16 -g 1 facp.aml  | sed 's/^0000/    /' >> acpidump.log
$ echo "" >> acpidump.log

Develop a Customized DSDT table

A Differentiated System Description Table (DSDT) is designed to provide OEM’s value-added features. A dummy DSDT can be generated as below, and OEM value-added features, such as ACPI battery or hotkey for airplane mode, can be added to it.

# Generate a DSDT
$ iasl -T DSDT
# Customize dsdt.asl
#  ex. adding an ACPI battery or airplane mode devices

Compile the DSDT table to binary

The customized DSDT can be compiled and appended to acpidump.log.

$ iasl dsdt.asl > /dev/zero
$ echo "DSDT @ 0x0000000000000000" >> acpidump.log
$ xxd -c 16 -g 1 dsdt.aml  | sed 's/^0000/    /' >> acpidump.log
$ echo "" >> acpidump.log

Run method test with acpidump.log

And finally, run the fwts method test.

$ fwts method --dumpfile=acpidump.log

Final Words

While we use DSDT as an example, the same technique applies to all ACPI tables. For instance, HMAT was introduced and frequently updated in recent ACPI specs, and the Firmware Test Suite includes most, if not all, changes up-to-date. As a consequence, FWTS is able to detect errors before firmware developers integrate HMAT into their projects, and therefore reduces errors in final products.

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