Try to HLT the processor during idlesyslinux-3.81-pre4

Try to HLT the processor during idle.  All the events we care about
should have interrupts associated with them, except possibly the
serial console.  Try to deal with the serial console by waiting some
time before going into HLT, and giving the user the option of enabling
the serial console interrupt, on the assumption that the BIOS will
simply IRET.

Signed-off-by: H. Peter Anvin <hpa@zytor.com>

1 files changed, 12 insertions, 0 deletions

diff --git a/doc/syslinux.txt b/doc/syslinux.txt
index 94141415..f654bffd 100644
--- a/doc/syslinux.txt
+++ b/doc/syslinux.txt
@@ -339,6 +339,7 @@ SERIAL port [[baudrate] flowcontrol]
 	"flowcontrol" is a combination of the following bits:
 	0x001 - Assert DTR
 	0x002 - Assert RTS
+	0x008 - Enable interrupts
 	0x010 - Wait for CTS assertion
 	0x020 - Wait for DSR assertion
 	0x040 - Wait for RI assertion
@@ -366,6 +367,17 @@ SERIAL port [[baudrate] flowcontrol]
 	ports detected by the BIOS.  They may or may not correspond to
 	the legacy port values 0x3F8, 0x2F8, 0x3E8, 0x2E8.
 
+	Enabling interrupts (setting the 0x008 bit) may give better
+	responsiveness without setting the NOHALT option, but could
+	potentially cause problems with buggy BIOSes.
+
+NOHALT flag_val
+	If flag_val is 1, don't halt the processor while idle.
+	Halting the processor while idle significantly reduces the
+	power consumption, but can cause poor responsiveness to the
+	serial console, especially when using scripts to drive the
+	serial console, as opposed to human interaction.
+
 CONSOLE flag_val
 	If flag_val is 0, disable output to the normal video console.
 	If flag_val is 1, enable output to the video console (this is