The Zana Zen

Hi All,

This post is more intended for Xen developers but you might be able to understand a thing or two.

ASL code exists in the DSDT and SSDT tables of ACPI. This code is provided by the system manufacturer and is intenteded to provide an abstract interface for configuring and accessing the hardware, especially those integrated parts such as the embedded controller, etc… The operating system has an interpreter which execute ASL in its context, this is how you write hardware specific code that can be executed on any ACPI compliant OS.

Part of my work now involves merging ACPI ASL bits in order to support PCI/PCIe pass-through capabilities. In order to debug ASL code, I’ve made a debug function which gets a string as an argument and then write each byte of the string to the IO port 0xE9, this port is being used by Xen for HVM debugging, so basically if you have your UART connected, all the strings will appear there.

Here is the code:

|     /* Debug ACPI using io-port 0xE9 */
|    OperationRegion (DBGP, SystemIO, 0xE9, 0×01)
|    Field (DBGP, ByteAcc, NoLock, Preserve)
|    {
|       /* HVM debug char */
|       HDBG, 8
|    }
|
|    Method (ZDBG, 1, NotSerialized)
|    {
|       /* Local0 - length of the debug string */
|       Store (SizeOf (Arg0), Local0)
|       Increment (Local0)
|       /* Init STR buffer from Arg0 */
|       Name (STR, Buffer (Local0) {})
|       Store (Arg0, STR)
|
|       /* Append prefix “ACPI-DBG: ” */
|       Name (PRFX, Buffer () {
|          0×41, 0×43, 0×50, 0×49, 0×2d,
|          0×44, 0×42, 0×47, 0×3a, 0×20
|       })
|
|       /* INPR -> Concatenated string with prefix */
|       Add (Local0, 0×0a, Local0)
|       Name (INPR, Buffer (Local0) {})
|       Concatenate (PRFX, STR, INPR)
|
|       /* Output string to ioport HDBG */
|       Store (Zero, Local1)
|       Decrement (Local0)
|       While (LLess (Local1, Local0))
|       {
|          Store (DerefOf (Index (INPR, Local1)), HDBG)
|          Increment (Local1)
|       }
|       /* End with a newline */
|       Store (0×0a, HDBG)
|    }

Thanks!

This entry was posted on Monday, July 21st, 2008 at 5:06 pm and is filed under programming, lowlevel. You can follow any responses to this entry through the RSS 2.0 feed. You can skip to the end and leave a response. Pinging is currently not allowed.