From: John Tsiombikas <nuclear@member.fsf.org>
Date: Sun, 29 Apr 2018 05:13:05 +0000 (+0300)
Subject: - memory detection with BIOS 0x15/0xe820
X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?p=bootcensus;a=commitdiff_plain;h=79be435fcf61613617025a2c4ef5fddf00a09178

- memory detection with BIOS 0x15/0xe820
- fixed video text scrolling in contty
---

diff --git a/src/boot/boot2.s b/src/boot/boot2.s
index d44b634..15b1cb1 100644
--- a/src/boot/boot2.s
+++ b/src/boot/boot2.s
@@ -34,6 +34,9 @@
 	# enable A20 address line
 	call enable_a20
 
+	# detect available memory
+	call detect_memory
+
 	# load the whole program into memory starting at 1MB
 	call load_main
 
@@ -554,6 +557,76 @@ kbc_wait_write:
 numbuf: .space 16
 
 
+	# sets the carry flag on failure
+detect_memory:
+	mov $buffer, %edi
+	xor %ebx, %ebx
+	mov $0x534d4150, %edx
+
+memdet_looptop:
+	mov $0xe820, %eax
+	mov $24, %ecx
+	int $0x15
+	jc memdet_fail
+	cmp $0x534d4150, %eax
+	jnz memdet_fail
+
+	mov buffer, %eax
+	mov $boot_mem_map, %esi
+	mov boot_mem_map_size, %ebp
+	# again, that's [ebp * 8 + esi]
+	mov %eax, (%esi,%ebp,8)
+
+	# only care for type 1 (usable ram), otherwise ignore
+	cmpl $1, 16(%edi)
+	jnz memdet_skip
+
+	# skip areas with 0 size (also clamp size to 4gb)
+	# test high 32bits
+	cmpl $0, 12(%edi)
+	jz memdet_highzero
+	# high part is non-zero, make low part ffffffff
+	xor %eax, %eax
+	not %eax
+	jmp 0f
+
+memdet_highzero:
+	# if both high and low parts are zero, ignore
+	mov 8(%edi), %eax
+	cmpl $0, %eax
+	jz memdet_skip
+
+0:	mov %eax, 4(%esi,%ebp,8)
+	incl boot_mem_map_size
+
+memdet_skip:
+	# terminate the loop if ebx was reset to 0
+	cmp $0, %ebx
+	jz memdet_done
+	jmp memdet_looptop
+
+memdet_done:
+	ret
+
+memdet_fail:
+	# if size > 0, then it's not a failure, just the end
+	cmpl $0, boot_mem_map_size
+	jnz memdet_done
+
+	# just panic...
+	mov $memdet_fail_msg, %esi
+	call putstr
+0:	hlt
+	jmp 0b
+
+memdet_fail_msg: .asciz "Failed to detect available memory!\n"
+
+	.global boot_mem_map_size
+boot_mem_map_size: .long 0
+	.global boot_mem_map
+boot_mem_map: .space 128
+
+
 # this is not boot loader code. It's called later on by the main kernel
 # code in 32bit protected mode. It's placed here because it needs to be
 # located in base memory as it returns and runs in real mode.
diff --git a/src/contty.c b/src/contty.c
index b8f8cde..606072c 100644
--- a/src/contty.c
+++ b/src/contty.c
@@ -175,7 +175,7 @@ static void scroll(void)
 
 	/* clear the next line that will be revealed by scrolling */
 	new_line = start_line + NROWS - 1;
-	memset16(TEXT_ADDR + new_line * NCOLS, VMEM_CHAR(' ', txattr), NCOLS);
+	memset16(TEXT_ADDR + new_line * NCOLS * 2, VMEM_CHAR(' ', txattr), NCOLS);
 	crtc_setstart(start_line);
 }
 
diff --git a/src/kmain.c b/src/kmain.c
index 0ffc152..d008217 100644
--- a/src/kmain.c
+++ b/src/kmain.c
@@ -20,6 +20,7 @@ along with this program.  If not, see <https://www.gnu.org/licenses/>.
 #include <ctype.h>
 #include "segm.h"
 #include "intr.h"
+#include "mem.h"
 #include "keyb.h"
 #include "timer.h"
 #include "contty.h"
@@ -32,8 +33,11 @@ void pcboot_main(void)
 {
 	init_segm();
 	init_intr();
-	kb_init();
+
 	con_init();
+	kb_init();
+
+	init_mem();
 
 	/* initialize the timer */
 	init_timer();
diff --git a/src/mem.c b/src/mem.c
new file mode 100644
index 0000000..1d5db9e
--- /dev/null
+++ b/src/mem.c
@@ -0,0 +1,44 @@
+/*
+pcboot - bootable PC demo/game kernel
+Copyright (C) 2018  John Tsiombikas <nuclear@member.fsf.org>
+
+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 <https://www.gnu.org/licenses/>.
+*/
+#include <stdio.h>
+#include "panic.h"
+#include "mem.h"
+
+struct mem_range {
+	uint32_t start;
+	uint32_t size;
+};
+
+#define MAX_MAP_SIZE	16
+extern struct mem_range boot_mem_map[MAX_MAP_SIZE];
+extern int boot_mem_map_size;
+
+void init_mem(void)
+{
+	int i;
+
+	if(boot_mem_map_size <= 0 || boot_mem_map_size > MAX_MAP_SIZE) {
+		panic("invalid memory map size reported by the boot loader: %d\n", boot_mem_map_size);
+	}
+
+	printf("Memory map:\n");
+	for(i=0; i<boot_mem_map_size; i++) {
+		printf(" start: %08x - size: %08x\n", (unsigned int)boot_mem_map[i].start,
+				(unsigned int)boot_mem_map[i].size);
+	}
+}
diff --git a/src/mem.h b/src/mem.h
new file mode 100644
index 0000000..219bf5f
--- /dev/null
+++ b/src/mem.h
@@ -0,0 +1,6 @@
+#ifndef MEM_H_
+#define MEM_H_
+
+void init_mem(void);
+
+#endif	/* MEM_H_ */