Merge pull request #80 from joeycastillo/lfs

Movement: add a lil file system with lfs

25 files changed, 870 insertions, 13 deletions

diff --git a/.gitmodules b/.gitmodules
index 89e424a9..54c3e634 100644
--- a/.gitmodules
+++ b/.gitmodules
@@ -1,3 +1,6 @@
 [submodule "tinyusb"]
 	path = tinyusb
 	url = https://github.com/hathach/tinyusb.git
+[submodule "littlefs"]
+	path = littlefs
+	url = https://github.com/littlefs-project/littlefs.git
diff --git a/Doxyfile b/Doxyfile
index 5d4a1fdb..d60bad9d 100644
--- a/Doxyfile
+++ b/Doxyfile
@@ -5,7 +5,7 @@
 #---------------------------------------------------------------------------
 DOXYFILE_ENCODING      = UTF-8
 PROJECT_NAME           = "Sensor Watch"
-PROJECT_NUMBER         = "0.0.1"
+PROJECT_NUMBER         = "0.0.2"
 PROJECT_BRIEF          = "A board replacement for the classic Casio F-91W wristwatch, powered by a Microchip SAM L22 microcontroller."
 PROJECT_LOGO           =
 OUTPUT_DIRECTORY       = "."
diff --git a/apps/eeprom-emulation-upgrade/Makefile b/apps/eeprom-emulation-upgrade/Makefile
new file mode 100755
index 00000000..5534c178
--- /dev/null
+++ b/apps/eeprom-emulation-upgrade/Makefile
@@ -0,0 +1,10 @@
+TOP = ../..
+include $(TOP)/make.mk
+
+INCLUDES += \
+  -I./
+
+SRCS += \
+  ./app.c
+
+include $(TOP)/rules.mk
diff --git a/apps/eeprom-emulation-upgrade/app.c b/apps/eeprom-emulation-upgrade/app.c
new file mode 100644
index 00000000..edd73e44
--- /dev/null
+++ b/apps/eeprom-emulation-upgrade/app.c
@@ -0,0 +1,62 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <peripheral_clk_config.h>
+#include "watch.h"
+
+void app_init(void) {
+}
+
+void app_wake_from_backup(void) {
+}
+
+void app_setup(void) {
+    delay_ms(5000);
+    while (!(NVMCTRL->INTFLAG.reg & NVMCTRL_INTFLAG_READY));
+    uint32_t user_row = (*((uint32_t *)NVMCTRL_AUX0_ADDRESS));
+    uint8_t eeprom = (user_row >> NVMCTRL_FUSES_EEPROM_SIZE_Pos) & 7;
+    printf("User row read successfully: 0x%lx\n", user_row);
+
+    if (eeprom != 1) {
+        user_row &= ~NVMCTRL_FUSES_EEPROM_SIZE_Msk;
+        user_row |= NVMCTRL_FUSES_EEPROM_SIZE(1);
+        if (NVMCTRL->STATUS.reg & NVMCTRL_STATUS_SB) {
+            printf("Secured bit was set; cannot perform upgrade.\n");
+            return;
+        }
+        printf("EEPROM configuration was %d.\nApplying change...\n", eeprom);
+
+        uint32_t temp = NVMCTRL->CTRLB.reg;                                     // Backup settings
+        NVMCTRL->CTRLB.reg = temp | NVMCTRL_CTRLB_CACHEDIS;                     // Disable Cache
+        NVMCTRL->STATUS.reg |= NVMCTRL_STATUS_MASK;                             // Clear error flags
+        NVMCTRL->ADDR.reg = NVMCTRL_AUX0_ADDRESS / 2;                           // Set address, command will be issued elsewhere
+        NVMCTRL->CTRLA.reg = NVMCTRL_CTRLA_CMD_EAR | NVMCTRL_CTRLA_CMDEX_KEY;   // Erase the user page
+        while (!(NVMCTRL->INTFLAG.reg & NVMCTRL_INTFLAG_READY));                // Wait for NVM command to complete
+        NVMCTRL->STATUS.reg |= NVMCTRL_STATUS_MASK;                             // Clear error flags
+        NVMCTRL->ADDR.reg = NVMCTRL_AUX0_ADDRESS / 2;                           // Set address, command will be issued elsewhere
+        NVMCTRL->CTRLA.reg = NVMCTRL_CTRLA_CMD_PBC | NVMCTRL_CTRLA_CMDEX_KEY;   // Erase the page buffer before buffering new data
+        while (!(NVMCTRL->INTFLAG.reg & NVMCTRL_INTFLAG_READY));                // Wait for NVM command to complete
+        NVMCTRL->STATUS.reg |= NVMCTRL_STATUS_MASK;                             // Clear error flags
+        NVMCTRL->ADDR.reg = NVMCTRL_AUX0_ADDRESS / 2;                           // Set address, command will be issued elsewhere
+        *((uint32_t *)NVMCTRL_AUX0_ADDRESS) = user_row;                         // write the new fuse values to the memory buffer
+        NVMCTRL->CTRLA.reg = NVMCTRL_CTRLA_CMD_WAP | NVMCTRL_CTRLA_CMDEX_KEY;   // Write the user page
+        NVMCTRL->CTRLB.reg = temp;                                              // Restore settings
+
+        printf("Done! Resetting...\n");
+        delay_ms(1000);
+        NVIC_SystemReset();
+    } else {
+        printf("EEPROM configuration was %d (8192 bytes). Upgrade successful!\n", eeprom);
+    }
+    printf("%d %d\n", eeprom, NVMCTRL->PARAM.bit.RWWEEP);
+}
+
+void app_prepare_for_standby(void) {
+}
+
+void app_wake_from_standby(void) {
+}
+
+bool app_loop(void) {
+    return true;
+}
diff --git a/apps/flash-test/Makefile b/apps/flash-test/Makefile
new file mode 100755
index 00000000..1e552265
--- /dev/null
+++ b/apps/flash-test/Makefile
@@ -0,0 +1,13 @@
+TOP = ../..
+include $(TOP)/make.mk
+
+INCLUDES += \
+  -I$(TOP)/littlefs/ \
+  -I./
+
+SRCS += \
+  $(TOP)/littlefs/lfs.c \
+  $(TOP)/littlefs/lfs_util.c \
+  ./app.c
+
+include $(TOP)/rules.mk
diff --git a/apps/flash-test/app.c b/apps/flash-test/app.c
new file mode 100644
index 00000000..17b1d0aa
--- /dev/null
+++ b/apps/flash-test/app.c
@@ -0,0 +1,131 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <peripheral_clk_config.h>
+#include "watch.h"
+#include "lfs.h"
+#include "hpl_flash.h"
+
+int lfs_storage_read(const struct lfs_config *cfg, lfs_block_t block, lfs_off_t off, void *buffer, lfs_size_t size);
+int lfs_storage_prog(const struct lfs_config *cfg, lfs_block_t block, lfs_off_t off, const void *buffer, lfs_size_t size);
+int lfs_storage_erase(const struct lfs_config *cfg, lfs_block_t block);
+int lfs_storage_sync(const struct lfs_config *cfg);
+
+int lfs_storage_read(const struct lfs_config *cfg, lfs_block_t block, lfs_off_t off, void *buffer, lfs_size_t size) {
+    (void) cfg;
+    return !watch_storage_read(block, off, (void *)buffer, size);
+}
+
+int lfs_storage_prog(const struct lfs_config *cfg, lfs_block_t block, lfs_off_t off, const void *buffer, lfs_size_t size) {
+    (void) cfg;
+    return !watch_storage_write(block, off, (void *)buffer, size);
+}
+
+int lfs_storage_erase(const struct lfs_config *cfg, lfs_block_t block) {
+    (void) cfg;
+    return !watch_storage_erase(block);
+}
+
+int lfs_storage_sync(const struct lfs_config *cfg) {
+    (void) cfg;
+    return !watch_storage_sync();
+}
+
+const struct lfs_config cfg = {
+    // block device operations
+    .read  = lfs_storage_read,
+    .prog  = lfs_storage_prog,
+    .erase = lfs_storage_erase,
+    .sync  = lfs_storage_sync,
+
+    // block device configuration
+    .read_size = 16,
+    .prog_size = NVMCTRL_PAGE_SIZE,
+    .block_size = NVMCTRL_ROW_SIZE,
+    .block_count = NVMCTRL_RWWEE_PAGES / 4,
+    .cache_size = NVMCTRL_PAGE_SIZE,
+    .lookahead_size = 16,
+    .block_cycles = 100,
+};
+
+lfs_t lfs;
+lfs_file_t file;
+
+static int _traverse_df_cb(void *p, lfs_block_t block){
+    (void) block;
+	uint32_t *nb = p;
+	*nb += 1;
+	return 0;
+}
+
+static int get_free_space(void){
+	int err;
+
+	uint32_t free_blocks = 0;
+	err = lfs_fs_traverse(&lfs, _traverse_df_cb, &free_blocks);
+	if(err < 0){
+		return err;
+	}
+
+	uint32_t available = cfg.block_count * cfg.block_size - free_blocks * cfg.block_size;
+
+	return available;
+}
+
+static void cb_tick(void) {
+    watch_date_time date_time = watch_rtc_get_date_time();
+    if (date_time.unit.second == 0) {
+        int err = lfs_mount(&lfs, &cfg);
+        if (err) {
+            printf("Mount failed: %d\n", err);
+        }
+        // read current count
+        uint32_t loop_count = 0;
+        lfs_file_open(&lfs, &file, "loop_count", LFS_O_RDWR | LFS_O_CREAT);
+        lfs_file_read(&lfs, &file, &loop_count, sizeof(loop_count));
+
+        // update loop count
+        loop_count += 1;
+        lfs_file_rewind(&lfs, &file);
+        lfs_file_write(&lfs, &file, &loop_count, sizeof(loop_count));
+
+        // remember the storage is not updated until the file is closed successfully
+        lfs_file_close(&lfs, &file);
+
+        // release any resources we were using
+        lfs_unmount(&lfs);
+
+        // print the boot count
+        printf("loop_count: %ld\n", loop_count);
+        printf("free space: %d\n", get_free_space());
+    }
+}
+
+void app_init(void) {
+}
+
+void app_wake_from_backup(void) {
+}
+
+void app_setup(void) {
+    // mount the filesystem
+    int err = lfs_mount(&lfs, &cfg);
+
+    // reformat if we can't mount the filesystem
+    // this should only happen on the first boot
+    if (err) {
+        lfs_format(&lfs, &cfg);
+        lfs_mount(&lfs, &cfg);
+    }
+    watch_rtc_register_tick_callback(cb_tick);
+}
+
+void app_prepare_for_standby(void) {
+}
+
+void app_wake_from_standby(void) {
+}
+
+bool app_loop(void) {
+    return true;
+}
diff --git a/littlefs b/littlefs
new file mode 160000
+Subproject 40dba4a556e0d81dfbe64301a6aa4e18ceca896
diff --git a/make.mk b/make.mk
index dacce3fa..0792e64f 100644
--- a/make.mk
+++ b/make.mk
@@ -113,6 +113,7 @@ SRCS += \
   $(TOP)/watch-library/hardware/watch/watch_i2c.c \
   $(TOP)/watch-library/hardware/watch/watch_spi.c \
   $(TOP)/watch-library/hardware/watch/watch_uart.c \
+  $(TOP)/watch-library/hardware/watch/watch_storage.c \
   $(TOP)/watch-library/hardware/watch/watch_deepsleep.c \
   $(TOP)/watch-library/hardware/watch/watch_private.c \
   $(TOP)/watch-library/hardware/watch/watch.c \
@@ -184,6 +185,7 @@ SRCS += \
   $(TOP)/watch-library/simulator/watch/watch_i2c.c \
   $(TOP)/watch-library/simulator/watch/watch_spi.c \
   $(TOP)/watch-library/simulator/watch/watch_uart.c \
+  $(TOP)/watch-library/simulator/watch/watch_storage.c \
   $(TOP)/watch-library/simulator/watch/watch_deepsleep.c \
   $(TOP)/watch-library/simulator/watch/watch_private.c \
   $(TOP)/watch-library/simulator/watch/watch.c \
diff --git a/movement/filesystem.c b/movement/filesystem.c
new file mode 100644
index 00000000..d122a7fa
--- /dev/null
+++ b/movement/filesystem.c
@@ -0,0 +1,245 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <peripheral_clk_config.h>
+#include "filesystem.h"
+#include "watch.h"
+#include "lfs.h"
+#include "hpl_flash.h"
+
+int lfs_storage_read(const struct lfs_config *cfg, lfs_block_t block, lfs_off_t off, void *buffer, lfs_size_t size);
+int lfs_storage_prog(const struct lfs_config *cfg, lfs_block_t block, lfs_off_t off, const void *buffer, lfs_size_t size);
+int lfs_storage_erase(const struct lfs_config *cfg, lfs_block_t block);
+int lfs_storage_sync(const struct lfs_config *cfg);
+
+int lfs_storage_read(const struct lfs_config *cfg, lfs_block_t block, lfs_off_t off, void *buffer, lfs_size_t size) {
+    (void) cfg;
+    return !watch_storage_read(block, off, (void *)buffer, size);
+}
+
+int lfs_storage_prog(const struct lfs_config *cfg, lfs_block_t block, lfs_off_t off, const void *buffer, lfs_size_t size) {
+    (void) cfg;
+    return !watch_storage_write(block, off, (void *)buffer, size);
+}
+
+int lfs_storage_erase(const struct lfs_config *cfg, lfs_block_t block) {
+    (void) cfg;
+    return !watch_storage_erase(block);
+}
+
+int lfs_storage_sync(const struct lfs_config *cfg) {
+    (void) cfg;
+    return !watch_storage_sync();
+}
+
+const struct lfs_config cfg = {
+    // block device operations
+    .read  = lfs_storage_read,
+    .prog  = lfs_storage_prog,
+    .erase = lfs_storage_erase,
+    .sync  = lfs_storage_sync,
+
+    // block device configuration
+    .read_size = 16,
+    .prog_size = NVMCTRL_PAGE_SIZE,
+    .block_size = NVMCTRL_ROW_SIZE,
+    .block_count = NVMCTRL_RWWEE_PAGES / 4,
+    .cache_size = NVMCTRL_PAGE_SIZE,
+    .lookahead_size = 16,
+    .block_cycles = 100,
+};
+
+static lfs_t lfs;
+static lfs_file_t file;
+static struct lfs_info info;
+
+static int _traverse_df_cb(void *p, lfs_block_t block) {
+    (void) block;
+	uint32_t *nb = p;
+	*nb += 1;
+	return 0;
+}
+
+int32_t filesystem_get_free_space(void) {
+	int err;
+
+	uint32_t free_blocks = 0;
+	err = lfs_fs_traverse(&lfs, _traverse_df_cb, &free_blocks);
+	if(err < 0){
+		return err;
+	}
+
+	uint32_t available = cfg.block_count * cfg.block_size - free_blocks * cfg.block_size;
+
+	return (int32_t)available;
+}
+
+static int filesystem_ls(lfs_t *lfs, const char *path) {
+    lfs_dir_t dir;
+    int err = lfs_dir_open(lfs, &dir, path);
+    if (err < 0) {
+        return err;
+    }
+
+    struct lfs_info info;
+    while (true) {
+        int res = lfs_dir_read(lfs, &dir, &info);
+        if (res < 0) {
+            return res;
+        }
+
+        if (res == 0) {
+            break;
+        }
+
+        switch (info.type) {
+            case LFS_TYPE_REG: printf("file "); break;
+            case LFS_TYPE_DIR: printf("dir  "); break;
+            default:           printf("?    "); break;
+        }
+
+        printf("%4ld bytes ", info.size);
+
+        printf("%s\n", info.name);
+    }
+
+    err = lfs_dir_close(lfs, &dir);
+    if (err < 0) {
+        return err;
+    }
+
+    return 0;
+}
+
+bool filesystem_init(void) {
+    int err = lfs_mount(&lfs, &cfg);
+
+    // reformat if we can't mount the filesystem
+    // this should only happen on the first boot
+    if (err < 0) {
+        printf("Ignore that error! Formatting filesystem...\n");
+        err = lfs_format(&lfs, &cfg);
+        if (err < 0) return false;
+        err = lfs_mount(&lfs, &cfg) == LFS_ERR_OK;
+        printf("Filesystem mounted with %ld bytes free.\n", filesystem_get_free_space());
+    }
+
+    return err == LFS_ERR_OK;
+}
+
+bool filesystem_file_exists(char *filename) {
+    info.type = 0;
+    lfs_stat(&lfs, filename, &info);
+    return info.type == LFS_TYPE_REG;
+}
+
+bool filesystem_rm(char *filename) {
+    info.type = 0;
+    lfs_stat(&lfs, filename, &info);
+    if (filesystem_file_exists(filename)) {
+        return lfs_remove(&lfs, filename) == LFS_ERR_OK;
+    } else {
+        printf("rm: %s: No such file\n", filename);
+        return false;
+    }
+}
+
+int32_t filesystem_get_file_size(char *filename) {
+    if (filesystem_file_exists(filename)) {
+        return info.size; // info struct was just populated by filesystem_file_exists
+    }
+
+    return -1;
+}
+
+bool filesystem_read_file(char *filename, char *buf, int32_t length) {
+    memset(buf, 0, length);
+    int32_t file_size = filesystem_get_file_size(filename);
+    if (file_size > 0) {
+        int err = lfs_file_open(&lfs, &file, filename, LFS_O_RDONLY);
+        if (err < 0) return false;
+        err = lfs_file_read(&lfs, &file, buf, min(length, file_size));
+        if (err < 0) return false;
+        return lfs_file_close(&lfs, &file) == LFS_ERR_OK;
+    }
+
+    return false;
+}
+
+static void filesystem_cat(char *filename) {
+    info.type = 0;
+    lfs_stat(&lfs, filename, &info);
+    if (filesystem_file_exists(filename)) {
+        if (info.size > 0) {
+            char *buf = malloc(info.size + 1);
+            filesystem_read_file(filename, buf, info.size);
+            printf("%s\n", buf);
+            free(buf);
+        } else {
+            printf("\n");
+        }
+    } else {
+        printf("cat: %s: No such file\n", filename);
+    }
+}
+
+bool filesystem_write_file(char *filename, char *text, int32_t length) {
+    int err = lfs_file_open(&lfs, &file, filename, LFS_O_RDWR | LFS_O_CREAT | LFS_O_TRUNC);
+    if (err < 0) return false;
+    err = lfs_file_write(&lfs, &file, text, length);
+    if (err < 0) return false;
+    return lfs_file_close(&lfs, &file) == LFS_ERR_OK;
+}
+
+void filesystem_process_command(char *line) {
+    printf("$ %s", line);
+    char *command = strtok(line, " \n");
+    
+    if (strcmp(command, "ls") == 0) {
+        char *directory = strtok(NULL, " \n");
+        if (directory == NULL) {
+            filesystem_ls(&lfs, "/");
+        } else {
+            printf("usage: ls\n");
+        }
+    } else if (strcmp(command, "cat") == 0) {
+        char *filename = strtok(NULL, " \n");
+        if (filename == NULL) {
+            printf("usage: cat file\n");
+        } else {
+            filesystem_cat(filename);
+        }
+    } else if (strcmp(command, "df") == 0) {
+        printf("free space: %ld bytes\n", filesystem_get_free_space());
+    } else if (strcmp(command, "rm") == 0) {
+        char *filename = strtok(NULL, " \n");
+        if (filename == NULL) {
+            printf("usage: rm file\n");
+        } else {
+            filesystem_rm(filename);
+        } 
+    } else if (strcmp(command, "echo") == 0) {
+        char *text = malloc(248);
+        memset(text, 0, 248);
+        size_t pos = 0;
+        char *word = strtok(NULL, " \n");
+        while (strcmp(word, ">")) {
+            sprintf(text + pos, "%s ", word);
+            pos += strlen(word) + 1;
+            word = strtok(NULL, " \n");
+            if (word == NULL) break;
+        }
+        text[strlen(text) - 1] = 0;
+        char *filename = strtok(NULL, " \n");
+        if (filename == NULL) {
+            printf("usage: echo text > file\n");
+        } else if (strchr(filename, '/') || strchr(filename, '\\')) {
+            printf("subdirectories are not supported\n");
+        } else {
+            filesystem_write_file(filename, text, strlen(text));
+        }
+        free(text);
+    } else {
+        printf("%s: command not found\n", command);
+    }
+}
diff --git a/movement/filesystem.h b/movement/filesystem.h
new file mode 100644
index 00000000..b0fb7f58
--- /dev/null
+++ b/movement/filesystem.h
@@ -0,0 +1,85 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2022 Joey Castillo
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+
+#ifndef FILESYSTEM_H_
+#define FILESYSTEM_H_
+#include <stdio.h>
+#include <stdbool.h>
+#include "watch.h"
+
+/** @brief Initializes and mounts the tiny 8kb filesystem, formatting it if need be.
+  * @return true if the filesystem was mounted successfully.
+  */
+bool filesystem_init(void);
+
+/** @brief Gets the space available on the filesystem.
+  * @return the free space in bytes
+  */
+int32_t filesystem_get_free_space(void);
+
+/** @brief Checks for the existence of a file on the filesystem.
+  * @param filename the file you wish to check
+  * @return true if the file exists; false otherwise
+  */
+bool filesystem_file_exists(char *filename);
+
+/** @brief Removes a file on the filesystem.
+  * @param filename the file you wish to remove
+  * @return true if the file was deleted successfully; false otherwise
+  */
+bool filesystem_rm(char *filename);
+
+/** @brief Gets the size of a file on the filesystem.
+  * @param filename the file whose size you wish to determine
+  * @return the file's size in bytes, or -1 if the file does not exist.
+  */
+int32_t filesystem_get_file_size(char *filename);
+
+/** @brief Reads a file from the filesystem into a buffer
+  * @param filename the file you wish to read
+  * @param buf A buffer of at least length bytes; the file will be read into this buffer
+  * @param length The number of bytes to read
+  * @return true if the read was successful; false otherwise
+  * @note This function will set buf to zero and read all bytes of the file into the buffer.
+  *       If you are reading a raw value (say you wrote a uint32 to a file), you can read back
+  *       the value by passing in the file's length for length. If you wish to treat the buffer
+  *       as a null-terminated string, allocate a buffer one byte longer than the file's length,
+  *       and the last byte will be guaranteed to be 0.
+  */
+bool filesystem_read_file(char *filename, char *buf, int32_t length);
+
+/** @brief Writes file to the filesystem
+  * @param filename the file you wish to write
+  * @param text The contents of the file
+  * @param length The number of bytes to write
+  * @return true if the write was successful; false otherwise
+  */
+bool filesystem_write_file(char *filename, char *text, int32_t length);
+
+/** @brief Handles the interactive file browser when Movement is plugged in to USB.
+  * @param line The command that the user typed into the serial console.
+  */
+void filesystem_process_command(char *line);
+
+#endif // FILESYSTEM_H_
diff --git a/movement/make/Makefile b/movement/make/Makefile
index 22e5f31b..05f3636c 100755
--- a/movement/make/Makefile
+++ b/movement/make/Makefile
@@ -16,6 +16,7 @@ INCLUDES += \
   -I../watch_faces/complication/ \
   -I../watch_faces/sensor/ \
   -I../watch_faces/demo/ \
+  -I../../littlefs/ \
   -I../lib/TOTP-MCU/ \
   -I../lib/sunriset/ \
   -I../lib/vsop87/ \
@@ -33,7 +34,10 @@ SRCS += \
   ../lib/sunriset/sunriset.c \
   ../lib/vsop87/vsop87a_milli.c \
   ../lib/astrolib/astrolib.c \
+  ../../littlefs/lfs.c \
+  ../../littlefs/lfs_util.c \
   ../movement.c \
+  ../filesystem.c \
   ../watch_faces/clock/simple_clock_face.c \
   ../watch_faces/clock/world_clock_face.c \
   ../watch_faces/clock/beats_face.c \
diff --git a/movement/movement.c b/movement/movement.c
index 361a7aa1..d79142ec 100644
--- a/movement/movement.c
+++ b/movement/movement.c
@@ -25,7 +25,11 @@
 #include <stdio.h>
 #include <string.h>
 #include <limits.h>
+#include <string.h>
+#include <stdlib.h>
+#include <stdio.h>
 #include "watch.h"
+#include "filesystem.h"
 #include "movement.h"
 
 #ifndef MOVEMENT_FIRMWARE
@@ -259,6 +263,8 @@ void app_init(void) {
     movement_state.next_available_backup_register = 4;
     _movement_reset_inactivity_countdown();
 
+    filesystem_init();
+
 #if __EMSCRIPTEN__
     int32_t time_zone_offset = EM_ASM_INT({
         return -new Date().getTimezoneOffset();
@@ -442,6 +448,32 @@ bool app_loop(void) {
         }
     }
 
+    // if we are plugged into USB, handle the file browser tasks
+    if (watch_is_usb_enabled()) {
+        char line[256] = {0};
+#if __EMSCRIPTEN__
+        // This is a terrible hack; ideally this should be handled deeper in the watch library.
+        // Alas, emscripten treats read() as something that should pop up an input box, so I
+        // wasn't able to implement this over there. I sense that this relates to read() being
+        // the wrong way to read data from USB (like we should be using fgets or something), but
+        // until I untangle that, this will have to do.
+        char *received_data = (char*)EM_ASM_INT({
+            var len = lengthBytesUTF8(tx) + 1;
+            var s = _malloc(len);
+            stringToUTF8(tx, s, len);
+            return s;
+        });
+        memcpy(line, received_data, min(255, strlen(received_data)));
+        free(received_data);
+        EM_ASM({
+            tx = "";
+        });
+#else
+        read(0, line, 256);
+#endif
+        if (strlen(line)) filesystem_process_command(line);
+    }
+
     event.subsecond = 0;
 
     return can_sleep && (movement_state.light_ticks == -1) && !movement_state.is_buzzing;
diff --git a/movement/watch_faces/sensor/accelerometer_data_acquisition_face.c b/movement/watch_faces/sensor/accelerometer_data_acquisition_face.c
index 6ef9c6db..9da8b35c 100644
--- a/movement/watch_faces/sensor/accelerometer_data_acquisition_face.c
+++ b/movement/watch_faces/sensor/accelerometer_data_acquisition_face.c
@@ -282,7 +282,7 @@ static void update(accelerometer_data_acquisition_state_t *state) {
 }
 
 static void update_settings(accelerometer_data_acquisition_state_t *state) {
-    char buf[12];
+    char buf[13];
     watch_clear_colon();
     if (state->beep_with_countdown) watch_set_indicator(WATCH_INDICATOR_BELL);
     else watch_clear_indicator(WATCH_INDICATOR_BELL);
diff --git a/watch-library/hardware/linker/saml22j18.ld b/watch-library/hardware/linker/saml22j18.ld
index a9801509..211e5346 100755
--- a/watch-library/hardware/linker/saml22j18.ld
+++ b/watch-library/hardware/linker/saml22j18.ld
@@ -32,11 +32,18 @@ OUTPUT_FORMAT("elf32-littlearm", "elf32-littlearm", "elf32-littlearm")
 OUTPUT_ARCH(arm)
 SEARCH_DIR(.)
 
-/* Memory Spaces Definitions */
+/* Memory Space Definitions:
+ *  0x00000000-0x00002000: Bootloader       (length  0x2000 or 8192 bytes)
+ *  0x00002000-0x0003C000: Firmware         (length 0x3A000 or 237568 bytes)
+ *  0x0003C000-0x00040000: EEPROM Emulation (length  0x2000 or 8192 bytes)
+ *  0x20000000-0x20008000: RAM              (length  0x8000 or 32768 bytes)
+ */
 MEMORY
 {
-  rom      (rx)  : ORIGIN = 0x2000, LENGTH = 0x00040000-0x2000
-  ram      (rwx) : ORIGIN = 0x20000000, LENGTH = 0x00008000
+  bootloader (rx)  : ORIGIN = 0x0, LENGTH = 0x2000
+  rom        (rx)  : ORIGIN = 0x2000, LENGTH = 0x00040000-0x2000-0x2000
+  eeprom     (r)   : ORIGIN = 0x00040000-0x2000, LENGTH = 0x2000
+  ram        (rwx) : ORIGIN = 0x20000000, LENGTH = 0x00008000
 }
 
 /* The stack size used by the application. NOTE: you need to adjust according to your application. */
diff --git a/watch-library/hardware/watch/watch.c b/watch-library/hardware/watch/watch.c
index 32bbccbb..b3dc4e8d 100644
--- a/watch-library/hardware/watch/watch.c
+++ b/watch-library/hardware/watch/watch.c
@@ -41,3 +41,7 @@ void SYSTEM_Handler(void) {
 bool watch_is_buzzer_or_led_enabled(void){
     return hri_mclk_get_APBCMASK_TCC0_bit(MCLK);
 }
+
+bool watch_is_usb_enabled(void) {
+    return USB->DEVICE.CTRLA.bit.ENABLE;
+}
diff --git a/watch-library/hardware/watch/watch_private.c b/watch-library/hardware/watch/watch_private.c
index 4b010d4a..cd607b8e 100644
--- a/watch-library/hardware/watch/watch_private.c
+++ b/watch-library/hardware/watch/watch_private.c
@@ -255,8 +255,15 @@ int _write(int file, char *ptr, int len) {
     return 0;
 }
 
-// this method could be overridden to read stuff from the USB console? but no need rn.
-int _read(void) {
+static char buf[256] = {0};
+
+int _read(int file, char *ptr, int len) {
+    (void)file;
+    int actual_length = strlen(buf);
+    if (actual_length) {
+        memcpy(ptr, buf, min(len, actual_length));
+        return actual_length;
+    }
     return 0;
 }
 
@@ -264,8 +271,17 @@ void USB_Handler(void) {
     tud_int_handler(0);
 }
 
+static void cdc_task(void) {
+    if (tud_cdc_n_available(0)) {
+        tud_cdc_n_read(0, buf, sizeof(buf));
+    } else {
+        memset(buf, 0, 256);
+    }
+}
+
 void TC0_Handler(void) {
     tud_task();
+    cdc_task();
     TC0->COUNT8.INTFLAG.reg |= TC_INTFLAG_OVF;
 }
 
diff --git a/watch-library/hardware/watch/watch_storage.c b/watch-library/hardware/watch/watch_storage.c
new file mode 100644
index 00000000..6c87be53
--- /dev/null
+++ b/watch-library/hardware/watch/watch_storage.c
@@ -0,0 +1,94 @@
+#include <stdlib.h>
+#include <string.h>
+#include <stdio.h>
+#include "watch_storage.h"
+
+#define RWWEE_ADDR_START NVMCTRL_RWW_EEPROM_ADDR
+#define RWWEE_ADDR_END (NVMCTRL_RWW_EEPROM_ADDR + NVMCTRL_PAGE_SIZE * NVMCTRL_RWWEE_PAGES)
+#define NVM_MEMORY ((volatile uint16_t *)FLASH_ADDR)
+
+static bool _is_valid_address(uint32_t addr, uint32_t size) {
+    if ((addr < NVMCTRL_RWW_EEPROM_ADDR) || (addr > (NVMCTRL_RWW_EEPROM_ADDR + NVMCTRL_PAGE_SIZE * NVMCTRL_RWWEE_PAGES))) {
+        return false;
+    }
+    if ((addr + size > (NVMCTRL_RWW_EEPROM_ADDR + NVMCTRL_PAGE_SIZE * NVMCTRL_RWWEE_PAGES))) {
+        return false;
+    }
+
+    return true;
+}
+
+bool watch_storage_read(uint32_t row, uint32_t offset, uint8_t *buffer, uint32_t size) {
+    uint32_t address = RWWEE_ADDR_START + row * NVMCTRL_ROW_SIZE + offset;
+    if (!_is_valid_address(address, size)) return false;
+
+    uint32_t nvm_address = address / 2;
+    uint32_t i;
+    uint16_t data;
+
+    watch_storage_sync();
+
+    if (address % 2) {
+        data      = NVM_MEMORY[nvm_address++];
+        buffer[0] = data >> 8;
+        i         = 1;
+    } else {
+        i = 0;
+    }
+
+    while (i < size) {
+        data = NVM_MEMORY[nvm_address++];
+        buffer[i] = (data & 0xFF);
+        if (i < (size - 1)) {
+            buffer[i + 1] = (data >> 8);
+        }
+        i += 2;
+    }
+    return true;
+}
+
+bool watch_storage_write(uint32_t row, uint32_t offset, const uint8_t *buffer, uint32_t size) {
+    uint32_t address = RWWEE_ADDR_START + row * NVMCTRL_ROW_SIZE + offset;
+    if (!_is_valid_address(address, size)) return false;
+
+    watch_storage_sync();
+
+    uint32_t nvm_address = address / 2;
+    uint16_t i, data;
+
+    hri_nvmctrl_write_CTRLA_reg(NVMCTRL, NVMCTRL_CTRLA_CMD_PBC | NVMCTRL_CTRLA_CMDEX_KEY);
+    watch_storage_sync();
+
+    for (i = 0; i < size; i += 2) {
+        data = buffer[i];
+        if (i < NVMCTRL_PAGE_SIZE - 1) {
+            data |= (buffer[i + 1] << 8);
+        }
+        NVM_MEMORY[nvm_address++] = data;
+    }
+    hri_nvmctrl_write_ADDR_reg(NVMCTRL, address / 2);
+    hri_nvmctrl_write_CTRLA_reg(NVMCTRL, NVMCTRL_CTRLA_CMD_RWWEEWP | NVMCTRL_CTRLA_CMDEX_KEY);
+
+    return true;
+}
+
+bool watch_storage_erase(uint32_t row) {
+    uint32_t address = RWWEE_ADDR_START + row * NVMCTRL_ROW_SIZE;
+    if (!_is_valid_address(address, NVMCTRL_ROW_SIZE)) return false;
+
+    watch_storage_sync();
+    hri_nvmctrl_write_ADDR_reg(NVMCTRL, address / 2);
+    hri_nvmctrl_write_CTRLA_reg(NVMCTRL, NVMCTRL_CTRLA_CMD_RWWEEER | NVMCTRL_CTRLA_CMDEX_KEY);
+
+    return true;
+}
+
+bool watch_storage_sync(void) {
+    while (!hri_nvmctrl_get_interrupt_READY_bit(NVMCTRL)) {
+        // wait for flash to become ready
+    }
+
+    hri_nvmctrl_clear_STATUS_reg(NVMCTRL, NVMCTRL_STATUS_MASK);
+
+    return true;
+}
diff --git a/watch-library/shared/watch/watch.h b/watch-library/shared/watch/watch.h
index ce85eed3..b94d36fb 100644
--- a/watch-library/shared/watch/watch.h
+++ b/watch-library/shared/watch/watch.h
@@ -64,6 +64,7 @@
 #include "watch_i2c.h"
 #include "watch_spi.h"
 #include "watch_uart.h"
+#include "watch_storage.h"
 #include "watch_deepsleep.h"
 
 #include "watch_private.h"
@@ -75,4 +76,16 @@
   */
 bool watch_is_buzzer_or_led_enabled(void);
 
+/** @brief Returns true if USB is enabled.
+  */
+bool watch_is_usb_enabled(void);
+
+/** @brief Reads up to len bytes from the USB serial.
+  * @param file ignored, you can pass in 0
+  * @param ptr pointer to a buffer of at least len bytes
+  * @param len the number of bytes you wish to read, max 256.
+  * @return The number of bytes read, or zero if no bytes were read.
+  */
+int read(int file, char *ptr, int len);
+
 #endif /* WATCH_H_ */
\ No newline at end of file
diff --git a/watch-library/shared/watch/watch_private.h b/watch-library/shared/watch/watch_private.h
index 7bb91d1f..9d55bc21 100644
--- a/watch-library/shared/watch/watch_private.h
+++ b/watch-library/shared/watch/watch_private.h
@@ -44,7 +44,8 @@ void _watch_enable_usb(void);
 // this function ends up getting called by printf to log stuff to the USB console.
 int _write(int file, char *ptr, int len);
 
-// this method could be overridden to read stuff from the USB console? but no need rn.
-int _read(void);
+// i thought this would be called by gets but it doesn't? anyway it does get called by read()
+// so that's our mechanism for reading data from the USB serial console.
+int _read(int file, char *ptr, int len);
 
 #endif
diff --git a/watch-library/shared/watch/watch_storage.h b/watch-library/shared/watch/watch_storage.h
new file mode 100644
index 00000000..6026cbcf
--- /dev/null
+++ b/watch-library/shared/watch/watch_storage.h
@@ -0,0 +1,92 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2020 Joey Castillo
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+#ifndef _WATCH_STORAGE_H_INCLUDED
+#define _WATCH_STORAGE_H_INCLUDED
+////< @file watch_storage.h
+
+#include "watch.h"
+
+#ifndef NVMCTRL_ROW_SIZE
+#define NVMCTRL_ROW_SIZE 256
+#endif
+#ifndef NVMCTRL_PAGE_SIZE
+#define NVMCTRL_PAGE_SIZE 64
+#endif
+#ifndef NVMCTRL_RWWEE_PAGES
+#define NVMCTRL_RWWEE_PAGES 128
+#endif
+
+/** @addtogroup storage Flash Storage
+  * @brief This section covers functions related to the SAM L22's 8 kilobyte EEPROM emulation area.
+  * @details The SAM L22 inside Sensor Watch has a 256 kilobyte Flash memory array that can be
+  *          programmed with whatever data we want. We use most of it to store the bootloader
+  *          and the application code that runs on your wrist. The bootloader region is read-only,
+  *          and the main application area is only writable by the bootloader (when you drag new
+  *          code onto the WATCHBOOT drive). However! there's also a special 8 kilobyte region
+  *          at the end of the Flash memory called the EEPROM Emulation Area. This EEPROM emulation
+  *          area can be written or erased while the main Flash array is being read. This makes it
+  *          super easy to work with, and useful for storing a small amount of non-volatile data that
+  *          persists across reboots, even when power is lost.
+  *          The functions in this section are very basic, and only cover reading and writing data
+  *          in this area. The region is laid out as 32 rows consisting of 4 pages of 64 bytes.
+  *          32*4*64 = 8192 bytes. The area can be written one page at a time, but it can only be
+  *          erased one row at a time. You can read at arbitrary word-aligned offsets within a row.
+  *
+  *                 ┌──────────────┬──────────────┬──────────────┬──────────────┐
+  *          Row 0  │   64 bytes   │   64 bytes   │   64 bytes   │   64 bytes   │
+  *                 ├──────────────┼──────────────┼──────────────┼──────────────┤
+  *          Row 1  │   64 bytes   │   64 bytes   │   64 bytes   │   64 bytes   │
+  *                 ├──────────────┼──────────────┼──────────────┼──────────────┤
+  *           ...   │              │              │              │              │
+  *                 ├──────────────┼──────────────┼──────────────┼──────────────┤
+  *          Row 31 │   64 bytes   │   64 bytes   │   64 bytes   │   64 bytes   │
+  *                 └──────────────┴──────────────┴──────────────┴──────────────┘
+  */
+/// @{
+/** @brief Reads a range of bytes from the storage area.
+  * @param row The row you want to read.
+  * @param offset The offset from the beginning of the row.
+  * @param buffer A buffer of at least `size` bytes.
+  * @param size The number of bytes you wish to read.
+  */
+bool watch_storage_read(uint32_t row, uint32_t offset, uint8_t *buffer, uint32_t size);
+
+/** @brief Writes bytes to a page in the storage area. Note that the row should already be erased before writing.
+  * @param row The row containing the page you want to write.
+  * @param offset The offset from the beginning of the row. Must be a multiple of 64.
+  * @param buffer The buffer containing the bytes you wish to set.
+  * @param size The number of bytes you wish to write.
+  */
+bool watch_storage_write(uint32_t row, uint32_t offset, const uint8_t *buffer, uint32_t size);
+
+/** @brief Erases a row in the storage area, setting all its bytes to 0xFF.
+  * @param row The row you want to erase.
+  */
+bool watch_storage_erase(uint32_t row);
+
+/** @brief Waits for any pending writes to complete.
+  */
+bool watch_storage_sync(void);
+/// @}
+#endif
diff --git a/watch-library/simulator/main.c b/watch-library/simulator/main.c
index 14bf44e6..ac9db6ac 100644
--- a/watch-library/simulator/main.c
+++ b/watch-library/simulator/main.c
@@ -102,8 +102,6 @@ static void main_loop_set_sleeping(bool sleeping) {
 }
 
 int main(void) {
-    printf("Hello, world!\n");
-
     app_init();
     _watch_init();
     app_setup();
diff --git a/watch-library/simulator/shell.html b/watch-library/simulator/shell.html
index 2f560aba..80e1e2ea 100644
--- a/watch-library/simulator/shell.html
+++ b/watch-library/simulator/shell.html
@@ -323,6 +323,9 @@
 
 <button onclick="getLocation()">Set location register (will prompt for access)</button>
 <br>
+<input id="input" style="width: 500px"></input>
+<button id="submit" onclick="sendText()">Send</button>
+<br>
 <textarea id="output" rows="8" style="width: 100%"></textarea>
 
 <script type='text/javascript'>
@@ -365,10 +368,16 @@
   };
   lat = 0;
   lon = 0;
+  tx = "";
   function updateLocation(location) {
     lat = Math.round(location.coords.latitude * 100);
     lon = Math.round(location.coords.longitude * 100);
   }
+  function sendText() {
+    var inputElement = document.getElementById('input');
+    tx = inputElement.value + "\n";
+    inputElement.value = "";
+  }
   function showError(error) {
     switch(error.code) {
       case error.PERMISSION_DENIED:
diff --git a/watch-library/simulator/watch/watch.c b/watch-library/simulator/watch/watch.c
index 1c965aad..749651af 100644
--- a/watch-library/simulator/watch/watch.c
+++ b/watch-library/simulator/watch/watch.c
@@ -3,3 +3,7 @@
 bool watch_is_buzzer_or_led_enabled(void) {
     return false;
 }
+
+bool watch_is_usb_enabled(void) {
+    return true;
+}
diff --git a/watch-library/simulator/watch/watch_private.c b/watch-library/simulator/watch/watch_private.c
index 4ddc2182..3425341a 100644
--- a/watch-library/simulator/watch/watch_private.c
+++ b/watch-library/simulator/watch/watch_private.c
@@ -63,7 +63,7 @@ int _write(int file, char *ptr, int len) {
     return 0;
 }
 
-// this method could be overridden to read stuff from the USB console? but no need rn.
-int _read(void) {
+int _read(int file, char *ptr, int len) {
+    // TODO: hook to UI
     return 0;
 }
diff --git a/watch-library/simulator/watch/watch_storage.c b/watch-library/simulator/watch/watch_storage.c
new file mode 100644
index 00000000..27011807
--- /dev/null
+++ b/watch-library/simulator/watch/watch_storage.c
@@ -0,0 +1,32 @@
+#include <stdlib.h>
+#include <stdio.h>
+#include <string.h>
+#include "watch_storage.h"
+
+uint8_t storage[NVMCTRL_ROW_SIZE * NVMCTRL_RWWEE_PAGES];
+
+bool watch_storage_read(uint32_t row, uint32_t offset, uint8_t *buffer, uint32_t size) {
+    // printf("read row %ld offset %ld size %ld\n", row, offset, size);
+    memcpy(buffer, storage + row * NVMCTRL_ROW_SIZE + offset, size);
+
+    return true;
+}
+
+bool watch_storage_write(uint32_t row, uint32_t offset, const uint8_t *buffer, uint32_t size) {
+    // printf("write row %ld offset %ld size %ld\n", row, offset, size);
+    memcpy(storage + row * NVMCTRL_ROW_SIZE + offset, buffer, size);
+
+    return true;
+}
+
+bool watch_storage_erase(uint32_t row) {
+    // printf("erase row %ld\n", row);
+    memset(storage + row * NVMCTRL_ROW_SIZE, 0xff, NVMCTRL_ROW_SIZE);
+
+    return true;
+}
+
+bool watch_storage_sync(void) {
+    // nothing to do here!
+    return true;
+}