# HG changeset patch
# User Paul Boddie <paul@boddie.org.uk>
# Date 1495402708 -7200
# Node ID d2f661d6db880450a046aae94b916cc0cc153e05
# Parent  b7d5babb9337d583165afe7af3474994744279a9
Added a test pattern generating routine.

diff -r b7d5babb9337 -r d2f661d6db88 vga.S
--- a/vga.S	Sun May 21 23:37:35 2017 +0200
+++ b/vga.S	Sun May 21 23:38:28 2017 +0200
@@ -589,6 +589,78 @@
 
 
 
+init_framebuffer_with_pattern:
+	li $v0, KSEG1_BASE
+	li $t8, SCREEN_SIZE
+	move $t2, $zero		/* x div 20 */
+	move $t3, $zero		/* x mod 20 */
+	move $t4, $zero		/* y mod 16 */
+	move $t5, $zero		/* base value: [(0...15) << 2] * 4 */
+	move $t6, $zero		/* offset value: [0...7] * 4 */
+
+_init_fbwp_loop:
+	li $t9, 0xfcfcfcfc
+	and $t9, $t9, $t5	/* get bits 5...2 of the base value */
+	or $t9, $t9, $t6	/* combine base<5:2> and offset values */
+
+	/* Test for bit 2 and set bit 7 if set, thus setting the intensity. */
+
+	andi $t7, $t5, 0b00000100
+	beqz $t7, _init_fbwp_loop_write
+	nop
+
+	li $t7, 0x80808080
+	or $t9, $t9, $t7	/* set intensity in each byte */
+
+_init_fbwp_loop_write:
+	sw $t9, 0($v0)
+	addiu $v0, $v0, 4
+
+	addiu $t3, $t3, 1	/* (x mod 20) += 1 */
+
+	/* Update the offset value every twenty pixels. */
+
+	addiu $t9, $t3, -5
+	bnez $t9, _init_fbwp_loop_end
+	nop
+
+	li $t9, 0x01010101
+	addu $t6, $t6, $t9	/* offset += [1] * 4 */
+	addiu $t2, $t2, 1	/* (x div 20) += 1 */
+	move $t3, $zero		/* (x mod 20) = 0 */
+
+	/* Test for the next line. */
+
+	addiu $t9, $t2, -8
+	bnez $t9, _init_fbwp_loop_end
+	nop
+
+	move $t2, $zero		/* (x div 20) = 0 */
+	move $t6, $zero		/* offset = 0 */
+
+_init_fbwp_loop_next_y:
+	addiu $t4, $t4, 1	/* (y mod 16) += 1 */
+
+	/* Update the base value every sixteen rows. */
+
+	addiu $t9, $t4, -16
+	bnez $t9, _init_fbwp_loop_end
+	nop
+
+	li $t9, 0x04040404
+	addu $t5, $t5, $t9	/* base += [(1 << 2)] * 4 */
+	move $t4, $zero		/* (y mod 16) = 0 */
+
+_init_fbwp_loop_end:
+	addiu $t8, $t8, -4
+	bnez $t8, _init_fbwp_loop
+	nop
+
+	jr $ra
+	nop
+
+
+
 /* Utilities. */
 
 handle_error_level: