Factor out precefaces and postfixes, apm_shutdown2

Makefile

@@ -5,7 +5,8 @@
 BITS ?= 32
 IN_EXT ?= .S
 LD ?= ld
-MYAS ?= as
+# Use gcc so that the preprocessor will run first.
+MYAS ?= gcc
 OBJ_EXT ?= .o
 OUT_EXT ?= .img
 RUN ?= bios_hello_world
@@ -22,7 +23,7 @@ all: $(OUTS)
 	$(LD) --oformat binary -o '$@' '$<' -T a.ld #-Ttext 0x7C00
 
 %$(OBJ_EXT): %$(IN_EXT)
-	$(MYAS) -o '$@' '$<'
+	$(MYAS) -c -o '$@' '$<'
 
 clean:
 	rm -f *$(OBJ_EXT) *$(OUT_EXT)

README.md

@@ -65,6 +65,20 @@ You cannot use any libraries, so how to do IO? Some ways that this can be done:
 - <https://en.wikipedia.org/wiki/VGA-compatible_text_mode>
 - VBE <https://en.wikipedia.org/wiki/VESA_BIOS_Extensions>
 
+Showdown and restart can be managed with either:
+
+-   ACPI <https://en.wikipedia.org/wiki/Advanced_Configuration_and_Power_Interface>
+
+    Newer and better.
+
+-   APM <https://en.wikipedia.org/wiki/Advanced_Power_Management>
+
+    <http://wiki.osdev.org/APM>
+
+    Older and simpler.
+
+See also: <http://wiki.osdev.org/Shutdown>
+
 ## Bibliography
 
 -   <http://stackoverflow.com/questions/22054578/run-a-program-without-an-operating-system>

apm_shutdown.S

@@ -1,5 +1,3 @@
-.code16
-
 /*
 http://wiki.osdev.org/Shutdown
 
@@ -8,6 +6,10 @@ http://stackoverflow.com/questions/678458/shutdown-the-computer-using-assembly
 http://stackoverflow.com/questions/3145569/how-to-power-down-the-computer-from-a-freestanding-environment
 */
 
+#include "common.h"
+
+BEGIN
+
 mov $0x5301, %ax
 xor %bx, %bx
 int $0x15
@@ -24,5 +26,4 @@ mov $0x0001, %bx
 mov $0x0003, %cx
 int $0x15
 
-.org 510
-.word 0xaa55
+END

apm_shutdown2.S

@@ -0,0 +1,70 @@
+/*
+Example from: http://wiki.osdev.org/APM
+
+Is all of this really needed? Compare to apm_shutdown.S.
+*/
+
+#include "common.h"
+
+BEGIN
+
+movb $0x53,%ah        #this is an APM command
+movb $0x0,%al         #installation check command
+xorw %bx,%bx          #device id (0 = APM BIOS)
+int $0x15             #call the BIOS function through interrupt 15h
+jc APM_error          #if the carry flag is set there was an error
+                      #the function was successful
+                      #AX = APM version number
+                          #AH = Major revision number (in BCD format)
+                          #AL = Minor revision number (also BCD format)
+                      #BX = ASCII characters "P" (in BH) and "M" (in BL)
+                      #CX = APM flags (see the official documentation for more details)
+
+#disconnect from any APM interface
+movb $0x53,%ah           #this is an APM command
+movb $0x4,%al            #interface disconnect command
+xorw %bx,%bx             #device id (0 = APM BIOS)
+int $0x15                #call the BIOS function through interrupt 15h
+jc .disconnect_error            #if the carry flag is set see what the fuss is about. 
+jmp .no_error
+
+.disconnect_error:        #the error code is in ah.
+cmpb $0x3,%ah            #if the error code is anything but 03h there was an error.
+jne APM_error            #the error code 03h means that no interface was connected in the first place.
+
+.no_error:
+                         #the function was successful
+                         #Nothing is returned.
+
+#connect to an APM interface
+movb $0x53,%ah           #this is an APM command
+movb $0x01,%al           #see above description
+xorw %bx,%bx             #device id (0 = APM BIOS)
+int $0x15                #call the BIOS function through interrupt 15h
+jc APM_error             #if the carry flag is set there was an error
+                         #the function was successful
+                         #The return values are different for each interface.
+                         #The Real Mode Interface returns nothing.
+                         #See the official documentation for the 
+                         #return values for the protected mode interfaces.
+
+#Enable power management for all devices
+movb $0x53,%ah          #this is an APM command
+movb $0x8,%al           #Change the state of power management...
+movw $0x001,%bx         #...on all devices to...
+movw $0x001,%cx         #...power management on.
+int $0x15               #call the BIOS function through interrupt 15h
+jc APM_error            #if the carry flag is set there was an error
+
+#Set the power state for all devices
+movb $0x53,%ah          #this is an APM command
+movb $0x07,%al          #Set the power state...
+movw $0x0001,%bx        #...on all devices to...
+movw $0x0003,%cx        #see above
+int $0x15               #call the BIOS function through interrupt 15h
+jc APM_error            #if the carry flag is set there was an error
+
+APM_error:
+hlt
+
+END

bios_hello_world.S

@@ -1,4 +1,5 @@
-.code16
+#include "common.h"
+BEGIN
     cli
     mov $msg, %si
     mov $0x0e, %ah
@@ -12,5 +13,4 @@ halt:
     hlt
 msg:
     .asciz "hello world"
-.org 510
-.word 0xaa55
+END

bios_one_char.S

@@ -1,10 +1,10 @@
 # Print a single `@` character with the BIOS.
 # More minimal than the hello world.
-.code16
+#include "common.h"
+BEGIN
 cli
 mov $0x40, %al
 mov $0x0e, %ah
 int $0x10
 hlt
-.org 510
-.word 0xaa55
+END

common.h

@@ -0,0 +1,3 @@
+#define BEGIN .code16
+#define END .org 510;\
+            .word 0xaa55