Synthesized FAT16 volume helpers for the USB-HS MRAM MSC demo. More...

#include "usb_msc_mram_hs_steps.h"
#include <stdint.h>
#include <string.h>

Include dependency graph for usb_msc_mram_hs_steps.c:

Enumerations
enum	demo_mram_t : uint32_t { k_mram_base_addr = 0x02000000U , k_mram_bytes = 0x00100000U }
	The MRAM window this volume exposes (RA8D2 HUM memory map). More...
enum	demo_fat_boot_t : uint32_t { k_boot_jmp0 = 0xEBU , k_boot_jmp1 = 0x3CU , k_boot_jmp2 = 0x90U , k_boot_media = 0xF8U , k_boot_sec_per_trk = 32U , k_boot_num_heads = 16U , k_boot_drive_num = 0x80U , k_boot_ext_sig = 0x29U , k_boot_volume_id = 0x52A8D200U , k_boot_sig_lo = 0x55U , k_boot_sig_hi = 0xAAU , k_boot_sig_lo_off = 510U , k_boot_sig_hi_off = 511U }
	Boot-sector field values (MS FAT spec 1.03 sec 3.1). More...
enum	demo_fat_off_t : uint8_t { k_bpb_off_jmp = 0U , k_bpb_off_oem = 3U , k_bpb_off_bps = 11U , k_bpb_off_spc = 13U , k_bpb_off_rsvd = 14U , k_bpb_off_nfats = 16U , k_bpb_off_rootent = 17U , k_bpb_off_totsec16 = 19U , k_bpb_off_media = 21U , k_bpb_off_fatsz16 = 22U , k_bpb_off_spt = 24U , k_bpb_off_heads = 26U , k_bpb_off_drvnum = 36U , k_bpb_off_bootsig = 38U , k_bpb_off_volid = 39U , k_bpb_off_label = 43U , k_bpb_off_fstype = 54U , k_dir_entry_bytes = 32U , k_dir_off_attr = 11U , k_dir_off_cluster_lo = 26U , k_dir_off_size = 28U , k_dir_attr_volume = 0x08U , k_dir_attr_read_only = 0x01U , k_dir_name_bytes = 11U , k_byte_shift = 8U , k_byte_mask = 0xFFU }
	Byte offsets inside the boot sector and directory entries. More...
enum	demo_word_pack_t : uint32_t { k_word_shift = 16U , k_word_mask = 0xFFFFU }
	32-bit little-endian split constants. More...

Functions
static void	demo_put16 (UCHAR *dst, uint16_t value)
	Write a 16-bit value little-endian into a byte buffer.
static void	demo_put32 (UCHAR *dst, uint32_t value)
	Write a 32-bit value little-endian into a byte buffer.
static void	demo_fat_fill_boot (UCHAR *out)
	Synthesize the FAT16 boot sector (MS FAT spec 1.03 sec 3.1).
static void	demo_fat_fill_fat (uint32_t fat_sector, UCHAR *out)
	Synthesize one FAT16 sector of the cluster chain.
static void	demo_fat_fill_root (uint32_t root_sector, UCHAR *out)
	Synthesize one root-directory sector.
void	demo_fat_fill_sector (uint32_t lba, UCHAR *out)
	Synthesize one 512-byte sector of the read-only volume.

Variables
static const UCHAR	s_fat_oem_name [8] = {'R', 'A', '8', 'D', '2', 'F', 'W', ' '}
	Boot-sector OEM name (8 bytes, space padded).
static const UCHAR	s_fat_volume_label [11] = {'R', 'A', '8', 'D', '2', ' ', 'M', 'R', 'A', 'M', ' '}
	Volume label, 11 bytes space padded (also the root entry).
static const UCHAR	s_fat_fs_type [8] = {'F', 'A', 'T', '1', '6', ' ', ' ', ' '}
	Filesystem-type tag, 8 bytes space padded.
static const UCHAR	s_fat_file_name [11] = {'M', 'R', 'A', 'M', ' ', ' ', ' ', ' ', 'B', 'I', 'N'}
	8.3 directory name of the exposed file: "MRAM.BIN".

Detailed Description

Synthesized FAT16 volume helpers for the USB-HS MRAM MSC demo.

Tag: [Ring 6 / APP] {World: S}

Implements the read-only FAT16 sector-synthesis routines split out of main.c so every translation unit stays under the source-size cap. The boot sector, FAT, and root directory are generated on the fly, and the data clusters map 1:1 onto the chip's 1 MiB MRAM window at 0x02000000, exposed as a single root file MRAM.BIN. Only demo_fat_fill_sector() is exported (called from the MSC media-read callback in main.c); the boot/FAT/root fillers and the little-endian packers stay private to this sibling, alongside the file-static FAT identifier strings and the FAT-specific layout enums.

Author: Brighton Sikarskie

Date: 2026-05-02

Copyright: Copyright (c) 2026 Brighton Sikarskie SPDX-License-Identifier: MIT

Since: 0.1.0

Definition in file usb_msc_mram_hs_steps.c.

Enumeration Type Documentation

◆ demo_fat_boot_t

enum demo_fat_boot_t : uint32_t

Boot-sector field values (MS FAT spec 1.03 sec 3.1).

Enumerator
k_boot_jmp0	Short JMP opcode.
k_boot_jmp1	JMP displacement.
k_boot_jmp2	NOP.
k_boot_media	Fixed-disk media byte.
k_boot_sec_per_trk	Geometry filler.
k_boot_num_heads	Geometry filler.
k_boot_drive_num	BIOS drive number.
k_boot_ext_sig	Extended boot signature.
k_boot_volume_id	Arbitrary volume serial.
k_boot_sig_lo	Boot signature low byte.
k_boot_sig_hi	Boot signature high byte.
k_boot_sig_lo_off	Signature low-byte offset.
k_boot_sig_hi_off	Signature high-byte offset.

Definition at line 46 of file usb_msc_mram_hs_steps.c.

◆ demo_fat_off_t

enum demo_fat_off_t : uint8_t

Byte offsets inside the boot sector and directory entries.

Enumerator
k_bpb_off_jmp	Jump instruction.
k_bpb_off_oem	OEM name (8 bytes).
k_bpb_off_bps	Bytes per sector.
k_bpb_off_spc	Sectors per cluster.
k_bpb_off_rsvd	Reserved sector count.
k_bpb_off_nfats	Number of FATs.
k_bpb_off_rootent	Root entry count.
k_bpb_off_totsec16	Total sectors (16-bit).
k_bpb_off_media	Media descriptor.
k_bpb_off_fatsz16	Sectors per FAT.
k_bpb_off_spt	Sectors per track.
k_bpb_off_heads	Head count.
k_bpb_off_drvnum	Drive number.
k_bpb_off_bootsig	Extended boot signature.
k_bpb_off_volid	Volume serial (4 bytes).
k_bpb_off_label	Volume label (11 bytes).
k_bpb_off_fstype	Filesystem type (8 bytes).
k_dir_entry_bytes	Directory entry size.
k_dir_off_attr	Attribute byte.
k_dir_off_cluster_lo	First cluster (low word).
k_dir_off_size	File size (32-bit LE).
k_dir_attr_volume	Volume-label attribute.
k_dir_attr_read_only	Read-only attribute.
k_dir_name_bytes	8.3 name field length.
k_byte_shift	Bits per byte for LE packing.
k_byte_mask	Low-byte mask.

Definition at line 66 of file usb_msc_mram_hs_steps.c.

◆ demo_mram_t

enum demo_mram_t : uint32_t

The MRAM window this volume exposes (RA8D2 HUM memory map).

Enumerator
k_mram_base_addr	MRAM code window base address.
k_mram_bytes	1 MiB window size.

Definition at line 37 of file usb_msc_mram_hs_steps.c.

◆ demo_word_pack_t

enum demo_word_pack_t : uint32_t

32-bit little-endian split constants.

Enumerator
k_word_shift	Bits per half-word.
k_word_mask	Low half-word mask.

Definition at line 99 of file usb_msc_mram_hs_steps.c.

Function Documentation

◆ demo_fat_fill_boot()

void demo_fat_fill_boot ( UCHAR * out )

static

Synthesize the FAT16 boot sector (MS FAT spec 1.03 sec 3.1).

Parameters

[out] out Zeroed 512-byte sector buffer.

Precondition: out is zeroed.; Geometry constants describe a valid FAT16 volume.

Postcondition: out holds the BPB + 0x55AA signature.; No other state changes.

Note: Pure function.

Since: 0.1.0

Definition at line 169 of file usb_msc_mram_hs_steps.c.

References demo_put16(), demo_put32(), k_boot_drive_num, k_boot_ext_sig, k_boot_jmp0, k_boot_jmp1, k_boot_jmp2, k_boot_media, k_boot_num_heads, k_boot_sec_per_trk, k_boot_sig_hi, k_boot_sig_hi_off, k_boot_sig_lo, k_boot_sig_lo_off, k_boot_volume_id, k_bpb_off_bootsig, k_bpb_off_bps, k_bpb_off_drvnum, k_bpb_off_fatsz16, k_bpb_off_fstype, k_bpb_off_heads, k_bpb_off_jmp, k_bpb_off_label, k_bpb_off_media, k_bpb_off_nfats, k_bpb_off_oem, k_bpb_off_rootent, k_bpb_off_rsvd, k_bpb_off_spc, k_bpb_off_spt, k_bpb_off_totsec16, k_bpb_off_volid, k_demo_block_size, k_fat_fat_sectors, k_fat_num_fats, k_fat_reserved_sectors, k_fat_root_entries, k_fat_total_sectors, memcpy(), s_fat_fs_type, s_fat_oem_name, and s_fat_volume_label.

Referenced by demo_fat_fill_sector().

◆ demo_fat_fill_fat()

void demo_fat_fill_fat	(	uint32_t	fat_sector,
		UCHAR *	out )

static

Synthesize one FAT16 sector of the cluster chain.

MRAM.BIN occupies clusters 2..2049 as one sequential chain (entry c -> c + 1, last entry -> end-of-chain). Entries 0/1 carry the media descriptor per the FAT spec; everything past the chain reads as free (0x0000).

Parameters

[in]	fat_sector	Index of the FAT sector (0-based).
[out]	out	Zeroed 512-byte sector buffer.

Precondition: out is zeroed.; fat_sector is below k_fat_fat_sectors.

Postcondition: out holds 256 little-endian FAT16 entries.; No other state changes.

Note: Pure function.

Since: 0.1.0

Definition at line 213 of file usb_msc_mram_hs_steps.c.

References demo_put16(), k_fat_entries_per_sec, k_fat_entry0, k_fat_eoc, and k_fat_last_mram_clus.

Referenced by demo_fat_fill_sector().

◆ demo_fat_fill_root()

void demo_fat_fill_root	(	uint32_t	root_sector,
		UCHAR *	out )

static

Synthesize one root-directory sector.

Sector 0 of the root carries two entries: the volume label and the read-only MRAM.BIN file (start cluster 2, size 1 MiB). Every other root sector is empty.

Parameters

[in]	root_sector	Index of the root sector (0-based).
[out]	out	Zeroed 512-byte sector buffer.

Precondition: out is zeroed.; root_sector is below k_fat_root_sectors.

Postcondition: out holds the directory entries for that sector.; No other state changes.

Note: Pure function.

Since: 0.1.0

Definition at line 252 of file usb_msc_mram_hs_steps.c.

References demo_put16(), demo_put32(), k_dir_attr_read_only, k_dir_attr_volume, k_dir_entry_bytes, k_dir_name_bytes, k_dir_off_attr, k_dir_off_cluster_lo, k_dir_off_size, k_fat_first_cluster, k_mram_bytes, memcpy(), s_fat_file_name, and s_fat_volume_label.

Referenced by demo_fat_fill_sector().

◆ demo_fat_fill_sector()

void demo_fat_fill_sector	(	uint32_t	lba,
		UCHAR *	out )

Synthesize one 512-byte sector of the read-only volume.

Dispatches on the LBA: boot sector, FAT, root directory, or data region. Data sectors inside the MRAM.BIN chain are copied straight out of the 1 MiB MRAM window; padding clusters past the chain read as zeros.

Parameters

[in]	lba	Logical block address inside the volume.
[out]	out	512-byte destination buffer.

Precondition: lba is below k_fat_total_sectors (caller-checked).; out has 512 writable bytes.

Postcondition: out holds the synthesized sector content.; No other state changes.

Note: Reads chip MRAM directly; no caching.

Since: 0.1.0

Definition at line 268 of file usb_msc_mram_hs_steps.c.

References demo_fat_fill_boot(), demo_fat_fill_boot(), demo_fat_fill_fat(), demo_fat_fill_fat(), demo_fat_fill_root(), demo_fat_fill_root(), k_demo_block_size, k_fat_data_lba, k_fat_fat_lba, k_fat_first_cluster, k_fat_last_mram_clus, k_fat_root_lba, k_mram_base_addr, memcpy(), and memset().

Referenced by demo_msc_read().

◆ demo_put16()

void demo_put16	(	UCHAR *	dst,
		uint16_t	value )

static

Write a 16-bit value little-endian into a byte buffer.

Parameters

[out]	dst	Destination (2 bytes).
[in]	value	Value to store.

Precondition: dst has 2 writable bytes.; None beyond the buffer contract.

Postcondition: dst[0] holds the low byte, dst[1] the high byte.; No other state changes.

Note: Pure function.

Since: 0.1.0

Definition at line 130 of file usb_msc_mram_hs_steps.c.

References k_byte_mask, and k_byte_shift.

Referenced by demo_fat_fill_boot(), demo_fat_fill_fat(), demo_fat_fill_root(), and demo_put32().

◆ demo_put32()

void demo_put32	(	UCHAR *	dst,
		uint32_t	value )

static

Write a 32-bit value little-endian into a byte buffer.

Parameters

[out]	dst	Destination (4 bytes).
[in]	value	Value to store.

Precondition: dst has 4 writable bytes.; None beyond the buffer contract.

Postcondition: dst holds the four little-endian bytes of value.; No other state changes.

Note: Pure function.

Since: 0.1.0

Definition at line 150 of file usb_msc_mram_hs_steps.c.

References demo_put16(), k_word_mask, and k_word_shift.

Referenced by demo_fat_fill_boot(), and demo_fat_fill_root().

Variable Documentation

◆ s_fat_file_name

const UCHAR s_fat_file_name[11] = {'M', 'R', 'A', 'M', ' ', ' ', ' ', ' ', 'B', 'I', 'N'}

static

8.3 directory name of the exposed file: "MRAM.BIN".

Definition at line 114 of file usb_msc_mram_hs_steps.c.

◆ s_fat_fs_type

const UCHAR s_fat_fs_type[8] = {'F', 'A', 'T', '1', '6', ' ', ' ', ' '}

static

Filesystem-type tag, 8 bytes space padded.

Definition at line 111 of file usb_msc_mram_hs_steps.c.

◆ s_fat_oem_name

const UCHAR s_fat_oem_name[8] = {'R', 'A', '8', 'D', '2', 'F', 'W', ' '}

static

Boot-sector OEM name (8 bytes, space padded).

Definition at line 105 of file usb_msc_mram_hs_steps.c.

◆ s_fat_volume_label

const UCHAR s_fat_volume_label[11] = {'R', 'A', '8', 'D', '2', ' ', 'M', 'R', 'A', 'M', ' '}

static

Volume label, 11 bytes space padded (also the root entry).

Definition at line 108 of file usb_msc_mram_hs_steps.c.

Enumerations

Functions

Variables

Detailed Description

Enumeration Type Documentation

◆ demo_fat_boot_t

◆ demo_fat_off_t

◆ demo_mram_t

◆ demo_word_pack_t

Function Documentation

◆ demo_fat_fill_boot()

◆ demo_fat_fill_fat()

◆ demo_fat_fill_root()

◆ demo_fat_fill_sector()

◆ demo_put16()

◆ demo_put32()

Variable Documentation

◆ s_fat_file_name

◆ s_fat_fs_type

◆ s_fat_oem_name

◆ s_fat_volume_label