diff --git a/src/interrupts.s b/src/interrupts.s
index d39e044..e565a0d 100644
--- a/src/interrupts.s
+++ b/src/interrupts.s
@@ -6,11 +6,23 @@
 
 #include "macros.h"
 
+; Return from a COP interrupt
 cop_rti		.macro
 	plb
 	rti
 	.endm
 
+; Set the data bank register to 0.
+set_dbr_0	.macro
+	pha
+	lda ##0
+	short_a
+	pha
+	plb
+	long_a
+	pla
+	.endm
+
 ; -----------------------------------------------------------------------------
 
 	.section near
@@ -121,18 +133,11 @@ cop_handler_native:
 	phb
 	long_a
 
-	; Set the data bank register to 0.
-	pha
-	lda ##0
-	short_a
-	pha
-	plb
-	long_a
-	pla
+	set_dbr_0
 
 	; First, we multiply the function number by 2, to get the jump
 	; table offset.
-
+	pha
 	txa
 	asl a
 	tax
@@ -182,8 +187,6 @@ cop_jump_table:
 	.word .word0 cop_exec
 	.word .word0 cop_exit
 	.word .word0 cop_volume_initialize
-	.word .word0 cop_get_environment_value
-	.word .word0 cop_set_environment_value
 	.word .word0 cop_ioctl
 
 ; -----------------------------------------------------------------------------
@@ -592,9 +595,9 @@ cop_set_working_directory:
 ; Given an open file handle, load the file into memory as a PGZ-format binary,
 ; and branch to its entry point. The user program will replace any user program
 ; already loaded and running, and will inherit the current environment and
-; file handles. This function is used by the shell, which suspends itself and
-; waits for the exit system call to pick up with the exit code of the user
-; program.
+; file handles. This call enters the user program by replacing the "return" vector
+; in the stack with the entry point of the user program, altering where the RTI
+; instruction "returns" to. The user program exits via a different system call.
 ;
 ; Arguments:
 ;		A: File handle
@@ -635,11 +638,5 @@ cop_exit:
 cop_volume_initialize:
 	cop_rti
 
-cop_get_environment_value:
-	cop_rti
-
-cop_set_environment_value:
-	cop_rti
-
 cop_ioctl:
 	cop_rti