# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1494802924 -7200
# Node ID 46c6e8d5307e73151023fcd0ce53c5e325451580
# Parent  4a66779421fc8701b43f2482b941ade12b045959
Tidied up the comments somewhat.

diff -r 4a66779421fc -r 46c6e8d5307e vga.S
--- a/vga.S	Sun May 14 23:41:30 2017 +0200
+++ b/vga.S	Mon May 15 01:02:04 2017 +0200
@@ -465,9 +465,6 @@
 	Initialise a line channel.
 	The line channel will be channel 0 (x = 0).
 
-	Once the hsync channel has completed a transfer, the line channel
-	transfer is initiated.
-
 	Specify a priority of 3:
 	DCHxCON<1:0> = CHPRI<1:0> = 3
 
@@ -483,6 +480,7 @@
 	Initiate channel transfers when the initiating interrupt condition
 	occurs:
 	DCHxECON<15:8> = CHSIRQ<7:0> = timer 2 interrupt
+	DCHxECON<4> = SIRQEN = 1
 	*/
 
 	la $v0, DCH0ECON
@@ -490,7 +488,7 @@
 	sw $v1, 0($v0)
 
 	/*
-	The line channel has a cell size of 160 bytes:
+	The line channel has a cell size as the number bytes in a line:
 	DCHxCSIZ<15:0> = CHCSIZ<15:0> = LINE_LENGTH
 	*/
 
@@ -499,8 +497,8 @@
 	sw $v1, 0($v0)
 
 	/*
-	Each source has a size identical to the cell size:
-	DCHxSSIZ<15:0> = CHSSIZ<15:0> = n
+	The source has a size identical to the cell size:
+	DCHxSSIZ<15:0> = CHSSIZ<15:0> = LINE_LENGTH
 	*/
 
 	la $v0, DCH0SSIZ
@@ -509,14 +507,14 @@
 
 	/*
 	The source address is the physical address of the line data:
-	DCHxSSA = line data physical address
+	DCHxSSA = physical(line data address)
 	*/
 
 	la $v0, DCH0SSA
 	sw $zero, 0($v0)
 
 	/*
-	Each destination has a size of 1 byte:
+	The destination has a size of 1 byte:
 	DCHxDSIZ<15:0> = CHDSIZ<15:0> = 1
 	*/
 
@@ -525,8 +523,8 @@
 	sw $v1, 0($v0)
 
 	/*
-	For the line channel, the destination address is the physical address of
-	PMDIN: DCHxDSA = physical(PMDIN)
+	The destination address is the physical address of PMDIN:
+	DCHxDSA = physical(PMDIN)
 	*/
 
 	la $v0, DCH0DSA
@@ -558,7 +556,7 @@
 	li $v1, (1 << 28)	/* IEC1<28> = DMA0IE = 1 */
 	sw $v1, SET($v0)
 
-	/* Enable channels. */
+	/* Enable channel. */
 
 	la $v0, DCH0CON
 	li $v1, 0b10000000
@@ -616,7 +614,7 @@
 	mtc0 $t3, CP0_DEBUG
 
 	mfc0 $t3, CP0_STATUS
-	li $t4, STATUS_BEV
+	li $t4, STATUS_BEV	/* BEV = 1 or EBASE cannot be set */
 	or $t3, $t3, $t4
 	mtc0 $t3, CP0_STATUS
 
@@ -629,11 +627,6 @@
 	li $t3, CAUSE_IV	/* IV = 1 (use EBASE+0x200 for interrupts) */
 	mtc0 $t3, CP0_CAUSE
 
-	/* Multiple vector...
-	la $t3, INTCON
-	li $t4, (1 << 12)
-	sw $t4, SET($t3) */
-
 	jr $ra
 	nop
 
@@ -643,8 +636,6 @@
 
 .section .flash, "a"
 
-/* Exception servicing. */
-
 exception_handler:
 	li $t8, 2500000
 exc_loop: