mirror of https://github.com/marqs85/ossc.git
139 lines
4.4 KiB
C
139 lines
4.4 KiB
C
//
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// Copyright (C) 2020 Ari Sundholm <megari@iki.fi>
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//
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// This file has been contributed to the Open Source Scan Converter project
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// developed by Markus Hiienkari Markus Hiienkari <mhiienka@niksula.hut.fi>
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// and other members of the retro gaming community.
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//
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// This program is free software: you can redistribute it and/or modify
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// it under the terms of the GNU General Public License as published by
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// the Free Software Foundation, either version 3 of the License, or
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// (at your option) any later version.
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//
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// This program is distributed in the hope that it will be useful,
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// but WITHOUT ANY WARRANTY; without even the implied warranty of
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// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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// GNU General Public License for more details.
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//
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// You should have received a copy of the GNU General Public License
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// along with this program. If not, see <http://www.gnu.org/licenses/>.
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//
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#include <string.h>
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#include "fat16_export.h"
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/*
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* The beginning of the boot sector. Will be followed by the BPB.
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* Offsets 0x000 to 0x00a, inclusive.
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*/
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static const alt_u8 bootsec_before_bpb_16[11] = {
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0xeb, 0x00, 0x90, 0x4d, 0x53, 0x57, 0x49, 0x4e, 0x34, 0x2e, 0x31,
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/* ^-----------^--- Maybe zero these? */
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};
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/* The BPB will span offsets 0x00b to 0x23, inclusive. Will be generated. */
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/*
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* The rest of the boot sector before the boot code and terminator.
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* Offsets 0x024 to 0x03d, inclusive.
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*/
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static const alt_u8 bootsec_after_bpb_16[26] = {
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0x80, 0x00, 0x29, 0xf4, 0xcf, 0xc6, 0x04, 0x4f, 0x53, 0x53, 0x43, 0x50,
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0x52, 0x4f, 0x46, 0x49, 0x4c, 0x53, 0x46, 0x41, 0x54, 0x31, 0x36, 0x20,
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0x20, 0x20,
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};
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/*
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* After this, we have the boot code (448 bytes) and sector terminator
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* (2 bytes). These will be generated.
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*/
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/* Generates a FAT16 boot sector.
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* buf must be at least FAT16_SECTOR_SIZE bytes long,
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* and is assumed to be pre-zeroed.
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*/
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void generate_boot_sector_16(alt_u8 *const buf) {
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/* Initial FAT16 boot sector contents. */
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memcpy(buf, bootsec_before_bpb_16, 11);
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/* BPB */
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buf[12] = 0x02;
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buf[13] = 0x04;
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buf[14] = 0x80;
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buf[16] = 0x02;
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buf[18] = 0x08;
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buf[20] = 0x80;
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buf[21] = 0xf8;
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buf[22] = 0x20;
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buf[24] = 0x3f;
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buf[26] = 0xff;
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/*
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* Then the rest of the boot sector.
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* The boot code is just 448 bytes of 0xf4.
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*/
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memcpy(buf + 36, bootsec_after_bpb_16, 26);
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memset(buf + 62, 0xf4, 448);
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buf[510] = 0x55;
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buf[511] = 0xaa;
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}
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/* The fixed 'preamble' of a FAT on a FAT16 volume. */
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static const alt_u8 fat16_preamble[4] = {
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0xf8, 0xff, 0xff, 0xff,
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};
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#if 0
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/*
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* To generate each FAT, we need 1040 bytes of memory.
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* The buffer is assumed to be zeroed out.
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* XXX: This is a problem!
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*/
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#define FAT16_ALLOC_SIZE 0x420U
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#endif
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/*
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* Generate a FAT.
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* The buffer is assumed to be zeroed out and have a size of at least
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* FAT16_SECTOR_SIZE bytes.
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* The number of clusters already written is given as an argument.
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* The function returns the total number of clusters written so far.
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*
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* The intention is to be able to generate and write the FAT in chunks
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* that do not exhaust all the remaining RAM.
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*/
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alt_u16 generate_fat16(alt_u8 *const fat, const alt_u16 written) {
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alt_u16 cur_ofs = 0;
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const alt_u16 start_cluster = 3U + written;
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const alt_u16 clusters_to_write = !written
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? ((FAT16_SECTOR_SIZE - sizeof(fat16_preamble)) >> FAT16_ENTRY_SHIFT)
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: (((514U - written) > (FAT16_SECTOR_SIZE >> FAT16_ENTRY_SHIFT))
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? (FAT16_SECTOR_SIZE >> FAT16_ENTRY_SHIFT)
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: (514U - written));
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const alt_u16 end_cluster = start_cluster + clusters_to_write;
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if (!written) {
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memcpy(fat, fat16_preamble, sizeof(fat16_preamble));
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cur_ofs += sizeof(fat16_preamble);
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}
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for (alt_u16 cluster = start_cluster; cluster < end_cluster; ++cluster) {
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/* FAT16 entries are 16-bit little-endian. */
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fat[cur_ofs++] = cluster & 0xffU;
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fat[cur_ofs++] = (cluster >> 8U) & 0xffU;
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}
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/* After the last cluster, write the chain terminator. */
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if (end_cluster == 514U) {
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fat[cur_ofs++] = 0xff;
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fat[cur_ofs++] = 0xff;
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}
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return end_cluster - 3U;
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}
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const alt_u8 prof_dirent_16[PROF_DIRENT_16_SIZE] = {
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0x4f, 0x53, 0x53, 0x43, 0x50, 0x52, 0x4f, 0x46, 0x42, 0x49, 0x4e, 0x20,
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0x00, 0x8e, 0x04, 0xb5, 0x6f, 0x51, 0x6f, 0x51, 0x00, 0x00, 0x17, 0x89,
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0x6f, 0x51, 0x02, 0x00, 0x00, 0x00, 0x10, 0x00,
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};
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