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760be1738e
Reorganize the and optimize the code to avoid redundant code and thus reduce code size, while making sure to zero-initialize the used areas on the SD card. These are the "clean" part of this change. The "dirty" part: Optimize the FAT16 export code further by introducing small deviations from the FAT16 specification. These deviations should not be harmful at all, unless the SD card is used for something requiring the jump instruction and/or boot code in the boot sector to be valid. This is typically only required when booting off the filesystem. After these changes, a considerable reduction in code size can be observed for sys_controller.elf and sys_onchip_memory2_0.bin: sys_controller.elf: text data bss dec hex filename 32392 2936 2652 37980 945c sys_controller.elf sys_onchip_memory2_0.bin: size: 35328 bytes This reduces the cost of the FAT16 export feature to 446 bytes.
84 lines
2.7 KiB
C
84 lines
2.7 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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#ifndef FAT16_EXPORT_H_
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#define FAT16_EXPORT_H_
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#include "alt_types.h"
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/* Use a sector size of 512 bytes. */
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#define FAT16_SECTOR_SIZE 512U
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/* This volume has 2048-byte clusters. */
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#define FAT16_CLUSTER_SIZE 2048U
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#define FAT16_SECTORS_PER_CLUSTER (FAT16_CLUSTER_SIZE/FAT16_SECTOR_SIZE)
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/* Offsets of the two File Allocation Tables. */
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#define FAT16_1_OFS 0x10000UL
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#define FAT16_2_OFS 0x14000UL
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/* Each FAT16 entry is a 16-bit little-endian integer. */
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#define FAT16_ENTRY_SIZE 2U
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#define FAT16_ENTRY_SHIFT 1U
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#define FAT16_ENTRIES_PER_SECTOR (FAT16_SECTOR_SIZE >> FAT16_ENTRY_SHIFT)
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/* On this volume, each FAT will be 16 kiB in size. */
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#define FAT16_SIZE 0x04000UL
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/* The first sector of the root directory. */
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#define FAT16_ROOT_DIR_FIRST_SECTOR 192U
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/* The length of the root directory in sectors. */
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#define FAT16_ROOT_DIR_SECTORS 128U
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/*
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* Define the properties and contents of the directory entry for the
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* settings file.
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*/
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#define PROF_DIRENT_16_OFS 0x18000UL
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#define PROF_DIRENT_16_SIZE 32U
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extern const alt_u8 prof_dirent_16[PROF_DIRENT_16_SIZE];
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#define PROF_16_DATA_OFS 0x028000UL
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#define PROF_16_DATA_SIZE 0x100000UL
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#define PROF_16_CLUSTER_COUNT (PROF_16_DATA_SIZE/FAT16_CLUSTER_SIZE)
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/* Profile file data starts at offset 0x00028000 */
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/* Profile file data ends at offset 0x00128000 */
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/* Profile file data is exactly 1 MiB long. */
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/* Generate a FAT16 boot sector.
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* buf must be at least FAT16_BOOT_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 *buf);
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/*
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* Generate a FAT of a FAT16 volume.
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* The buffer is assumed to be zeroed out and have a size of at least 512 bytes.
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* The number of clusters already written are 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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alt_u16 generate_fat16(void *buf, alt_u16 written);
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#endif // FAT16_EXPORT_H_
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