From 354c532e19d9ab338720f3031ba8a0787886f4ee Mon Sep 17 00:00:00 2001
From: Thomas White <taw@physics.org>
Date: Sat, 28 Jul 2018 20:42:25 +0200
Subject: Initial framebuffer stuff

---
 Makefile          |  4 +--
 src/framebuffer.s | 92 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/main.s        |  5 ++-
 src/ports.h       | 24 +++++++++++++++
 4 files changed, 122 insertions(+), 3 deletions(-)
 create mode 100644 src/framebuffer.s
 create mode 100644 src/ports.h

diff --git a/Makefile b/Makefile
index b10fe7a..2dc1ae5 100644
--- a/Makefile
+++ b/Makefile
@@ -1,5 +1,5 @@
-SRCS=main.s slow_status_flash.s  flash_button.s swi_handler.s
-OBJS=main.o slow_status_flash.o  flash_button.o swi_handler.o
+SRCS=main.s slow_status_flash.s flash_button.s swi_handler.s framebuffer.s
+OBJS=main.o slow_status_flash.o flash_button.o swi_handler.o framebuffer.o
 
 all: kernel.img
 
diff --git a/src/framebuffer.s b/src/framebuffer.s
new file mode 100644
index 0000000..ef3d9a1
--- /dev/null
+++ b/src/framebuffer.s
@@ -0,0 +1,92 @@
+/*
+ * framebuffer.s
+ *
+ * Copyright © 2018 Thomas White <taw@bitwiz.org.uk>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+.include "ports.h"
+
+.global framebuffer_init
+
+framebuffer_init:
+	STMDB	R13!, {R14}
+
+	ADR	R1, framebuffer_info
+	ADD	R1, R1, #0x40000000
+	MOV	R0, #1
+	BL	send_mailbox
+@	BL	read_mailbox
+
+	CMP	R1, #0
+	LDMNEIA	R13!, {PC}	@ Fail
+
+	LDMIA	R13!, {PC}
+
+
+/* ->  R0 = mailbox number
+ *     R1 = value to write */
+send_mailbox:
+	STMDB	R13!, {R2, R8, R14}
+	LDR	R8, =(PERIPHERAL_BASE+OFFS_MAILBOX)
+
+	/* Wait for empty mailbox */
+1:
+	LDR	R2, [R8, #18]
+	TST	R2, #1<<31
+	BNE	1b
+
+	AND	R2, R0, #0xf
+	ORR	R2, R2, R1
+	STR	R2, [R8, #20]
+
+	LDMIA	R13!, {R2, R8, PC}
+
+
+/* -> R0 = mailbox number
+ * <- R1 = value read */
+read_mailbox:
+	STMDB	R13!, {R2, R8, R14}
+	LDR	R8, =(PERIPHERAL_BASE+OFFS_MAILBOX)
+
+	/* Wait for non-empty mailbox */
+1:
+	LDR	R2, [R8, #18]
+	TST	R2, #1<<30
+	BNE	1b
+
+	LDR	R2, [R8, #0]
+	AND	R1, R2, #0xf
+	CMP	R1, R0
+	BNE	1b		@ Wrong mailbox
+
+	BIC	R1, R2, #0xf
+
+	LDMIA	R13!, {R2, R8, PC}
+
+
+.align 4
+framebuffer_info:
+	.int	1024
+	.int	768
+	.int	1024
+	.int	768
+	.int	0
+	.int	16
+	.int	0
+	.int	0
+	.int	0
+	.int	0
diff --git a/src/main.s b/src/main.s
index 40f3ff0..ca63640 100644
--- a/src/main.s
+++ b/src/main.s
@@ -19,6 +19,7 @@
  */
 
 .include "swi_numbers.h"
+.include "ports.h"
 
 .section .init
 
@@ -64,8 +65,10 @@ reset:
 	LDMIA	R10!, {R0-R7}
 	STMIA	R11!, {R0-R7}
 
+	BL	framebuffer_init
+
 	/* Configure GPIOs */
-	LDR	R8, =0x3f200000
+	LDR	R8, =(PERIPHERAL_BASE+OFFS_GPIO)
 	LDR	R1, [R8, #0x04]		@ GPFSEL1
 	ORR	R1, R1, #1<<18		@ GPIO pin 16 is output
 	BIC	R1, R1, #3<<21		@ GPIO pin 17 is input
diff --git a/src/ports.h b/src/ports.h
new file mode 100644
index 0000000..4f7e584
--- /dev/null
+++ b/src/ports.h
@@ -0,0 +1,24 @@
+/*
+ * ports.h
+ *
+ * Copyright © 2018 Thomas White <taw@bitwiz.org.uk>
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ *
+ */
+
+PERIPHERAL_BASE		= 0x3f000000
+
+OFFS_GPIO		= 0x00200000
+OFFS_MAILBOX		= 0x0000b880
-- 
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