Block devices

Table of Contents

• Operations
• Ramdisk
• Tests and validation

Sector storage for filesystems, and the ramdisk driver.

A block device stores 512-byte sectors and has no /dev file: a board's mounts section attaches a filesystem to it, and the generator builds the block_device_t that the filesystem receives. The interface is documented in Block devices; how filesystems use it is in Files and storage.

Compatible	Storage	Boards
homecore,ramdisk	A .bss buffer; lost at reset	LM3S6965EVB (32 KB, littlefs), STM32F4DISCOVERY (64 KB FAT, 16 KB littlefs)

Operations

Operation	Contract
read(device, sector, buf, count)	Copy count whole sectors into buf; 0, or -1 with errno
write(device, sector, buf, count)	Store count whole sectors; 0, or -1 with errno
sync(device)	Finish pending writes
sector_count(device)	The device size in sectors

A range past the end of the device fails with EIO and transfers nothing; a NULL buffer fails with EFAULT. Operations run in thread context only. There is no erase: current devices overwrite in place, and littlefs's erase callback does nothing.

Ramdisk

devices:
  ram0: {compatible: "homecore,ramdisk", size: 32K}
mounts:
  /ram: {device: ram0, fs: littlefs, format: true}

The size property, a multiple of 512, sizes a 4-byte-aligned buffer that the generator places in .bss, so it counts as static RAM in the linker map and reduces the heap by the same amount. The buffer starts zeroed, which holds no filesystem, so a ramdisk mount uses format: true. Transfers are memcpy calls; the ramdisk has no interrupts or hardware.

Tests and validation

tests/fat_test.c and tests/littlefs_test.c run the filesystems on ramdisks, up to a full volume, and tests/littlefs_test.c wraps the ramdisk in a device that fails writes to simulate resets. The ramdisk's own range and buffer checks have no dedicated test. The QEMU regression uses the LM3S6965EVB ramdisk through littlefs.