diff --git a/Makefile b/Makefile
index 2d3bdf92..583d8221 100644
--- a/Makefile
+++ b/Makefile
@@ -176,7 +176,7 @@ mongoose.c: Makefile $(wildcard src/*.c) $(wildcard src/drivers/*.c)
 	(cat src/license.h; echo; echo '#include "mongoose.h"' ; (for F in src/*.c src/drivers/*.c ; do echo; echo '#ifdef MG_ENABLE_LINES'; echo "#line 1 \"$$F\""; echo '#endif'; cat $$F | sed -e 's,#include ".*,,'; done))> $@
 
 mongoose.h: $(HDRS) Makefile
-	(cat src/license.h; echo; echo '#ifndef MONGOOSE_H'; echo '#define MONGOOSE_H'; echo; cat src/version.h ; echo; echo '#ifdef __cplusplus'; echo 'extern "C" {'; echo '#endif'; cat src/arch.h src/arch_*.h src/net_ft.h src/net_lwip.h src/net_rl.h src/config.h src/str.h src/queue.h src/fmt.h src/printf.h src/log.h src/timer.h src/fs.h src/util.h src/url.h src/iobuf.h src/base64.h src/md5.h src/sha1.h src/event.h src/net.h src/http.h src/ssi.h src/tls.h src/tls_mbed.h src/tls_openssl.h src/ws.h src/sntp.h src/mqtt.h src/dns.h src/json.h src/rpc.h src/ota.h src/sys.h src/net_builtin.h src/drivers/*.h | sed -e '/keep/! s,#include ".*,,' -e 's,^#pragma once,,'; echo; echo '#ifdef __cplusplus'; echo '}'; echo '#endif'; echo '#endif  // MONGOOSE_H')> $@
+	(cat src/license.h; echo; echo '#ifndef MONGOOSE_H'; echo '#define MONGOOSE_H'; echo; cat src/version.h ; echo; echo '#ifdef __cplusplus'; echo 'extern "C" {'; echo '#endif'; cat src/arch.h src/arch_*.h src/net_ft.h src/net_lwip.h src/net_rl.h src/config.h src/str.h src/queue.h src/fmt.h src/printf.h src/log.h src/timer.h src/fs.h src/util.h src/url.h src/iobuf.h src/base64.h src/md5.h src/sha1.h src/event.h src/net.h src/http.h src/ssi.h src/tls.h src/tls_mbed.h src/tls_openssl.h src/ws.h src/sntp.h src/mqtt.h src/dns.h src/json.h src/rpc.h src/ota.h src/device.h src/net_builtin.h src/drivers/*.h | sed -e '/keep/! s,#include ".*,,' -e 's,^#pragma once,,'; echo; echo '#ifdef __cplusplus'; echo '}'; echo '#endif'; echo '#endif  // MONGOOSE_H')> $@
 
 
 clean: clean_examples clean_embedded
diff --git a/examples/device-dashboard/net.c b/examples/device-dashboard/net.c
index a6423409..9155964e 100644
--- a/examples/device-dashboard/net.c
+++ b/examples/device-dashboard/net.c
@@ -222,7 +222,7 @@ static void handle_firmware_upload(struct mg_connection *c,
     mg_http_reply(c, 200, s_json_header, "true\n");
     if (data.len == 0) {
       // Successful mg_ota_end() called, schedule device reboot
-      mg_timer_add(c->mgr, 500, 0, (void (*)(void *)) mg_sys_reset, NULL);
+      mg_timer_add(c->mgr, 500, 0, (void (*)(void *)) mg_device_reset, NULL);
     }
   }
 }
@@ -250,9 +250,9 @@ static void handle_firmware_status(struct mg_connection *c) {
                 MG_FIRMWARE_CURRENT, print_status, MG_FIRMWARE_PREVIOUS);
 }
 
-static void handle_sys_reset(struct mg_connection *c) {
+static void handle_device_reset(struct mg_connection *c) {
   mg_http_reply(c, 200, s_json_header, "true\n");
-  mg_timer_add(c->mgr, 500, 0, (void (*)(void *)) mg_sys_reset, NULL);
+  mg_timer_add(c->mgr, 500, 0, (void (*)(void *)) mg_device_reset, NULL);
 }
 
 // HTTP request handler function
@@ -292,8 +292,8 @@ static void fn(struct mg_connection *c, int ev, void *ev_data, void *fn_data) {
       handle_firmware_rollback(c);
     } else if (mg_http_match_uri(hm, "/api/firmware/status")) {
       handle_firmware_status(c);
-    } else if (mg_http_match_uri(hm, "/api/sys/reset")) {
-      handle_sys_reset(c);
+    } else if (mg_http_match_uri(hm, "/api/device/reset")) {
+      handle_device_reset(c);
     } else {
       struct mg_http_serve_opts opts;
       memset(&opts, 0, sizeof(opts));
diff --git a/examples/device-dashboard/web_root/main.js b/examples/device-dashboard/web_root/main.js
index d08406bb..d7b87f4c 100644
--- a/examples/device-dashboard/web_root/main.js
+++ b/examples/device-dashboard/web_root/main.js
@@ -211,7 +211,7 @@ function FirmwareUpdate({}) {
   const oncommit = ev => fetch('api/firmware/commit')
     .then(r => r.json())
     .then(refresh);
-  const onreboot = ev => fetch('api/sys/reset')
+  const onreboot = ev => fetch('api/device/reset')
     .then(r => r.json())
     .then(r => new Promise(r => setTimeout(ev => { refresh(); r(); }, 3000)));
   const onrollback = ev => fetch('api/firmware/rollback')
diff --git a/examples/stm32/nucleo-h563zi-make-baremetal-builtin/mongoose_custom.h b/examples/stm32/nucleo-h563zi-make-baremetal-builtin/mongoose_custom.h
index 09860117..e751b193 100644
--- a/examples/stm32/nucleo-h563zi-make-baremetal-builtin/mongoose_custom.h
+++ b/examples/stm32/nucleo-h563zi-make-baremetal-builtin/mongoose_custom.h
@@ -2,7 +2,7 @@
 
 #define MG_ARCH MG_ARCH_NEWLIB
 #define MG_OTA MG_OTA_FLASH
-#define MG_SYS MG_SYS_STM32H5
+#define MG_DEVICE MG_DEVICE_STM32H5
 
 #define MG_ENABLE_TCPIP 1
 #define MG_ENABLE_CUSTOM_MILLIS 1
diff --git a/examples/stm32/nucleo-h743zi-make-baremetal-builtin/mongoose_custom.h b/examples/stm32/nucleo-h743zi-make-baremetal-builtin/mongoose_custom.h
index c965bdca..29a55da2 100644
--- a/examples/stm32/nucleo-h743zi-make-baremetal-builtin/mongoose_custom.h
+++ b/examples/stm32/nucleo-h743zi-make-baremetal-builtin/mongoose_custom.h
@@ -2,7 +2,7 @@
 
 #define MG_ARCH MG_ARCH_NEWLIB
 #define MG_OTA MG_OTA_FLASH
-#define MG_SYS MG_SYS_STM32H7
+#define MG_DEVICE MG_DEVICE_STM32H7
 
 #define MG_ENABLE_TCPIP 1
 #define MG_ENABLE_CUSTOM_MILLIS 1
diff --git a/mongoose.c b/mongoose.c
index 08aaa0aa..6fdd7444 100644
--- a/mongoose.c
+++ b/mongoose.c
@@ -112,6 +112,505 @@ size_t mg_base64_decode(const char *src, size_t n, char *dst, size_t dl) {
   return len;
 }
 
+#ifdef MG_ENABLE_LINES
+#line 1 "src/device_dummy.c"
+#endif
+
+
+#if MG_DEVICE == MG_DEVICE_NONE
+void *mg_flash_start(void) {
+  return NULL;
+}
+size_t mg_flash_size(void) {
+  return 0;
+}
+size_t mg_flash_sector_size(void) {
+  return 0;
+}
+size_t mg_flash_write_align(void) {
+  return 0;
+}
+int mg_flash_bank(void) {
+  return 0;
+}
+bool mg_flash_erase(void *location) {
+  (void) location;
+  return false;
+}
+bool mg_flash_swap_bank(void) {
+  return true;
+}
+bool mg_flash_write(void *addr, const void *buf, size_t len) {
+  (void) addr, (void) buf, (void) len;
+  return false;
+}
+void mg_device_reset(void) {
+}
+#endif
+
+#ifdef MG_ENABLE_LINES
+#line 1 "src/device_flash.c"
+#endif
+
+
+#if MG_DEVICE == MG_DEVICE_STM32H7 || MG_DEVICE == MG_DEVICE_STM32H5
+// Flash can be written only if it is erased. Erased flash is 0xff (all bits 1)
+// Writes must be mg_flash_write_align() - aligned. Thus if we want to save an
+// object, we pad it at the end for alignment.
+//
+// Objects in the flash sector are stored sequentially:
+// | 32-bit size | 32-bit KEY | ..data.. | ..pad.. | 32-bit size | ......
+//
+// In order to get to the next object, read its size, then align up.
+
+// Traverse the list of saved objects
+size_t mg_flash_next(char *p, char *end, uint32_t *key, size_t *size) {
+  size_t aligned_size = 0, align = mg_flash_write_align(), left = end - p;
+  uint32_t *p32 = (uint32_t *) p, min_size = sizeof(uint32_t) * 2;
+  if (p32[0] != 0xffffffff && left > MG_ROUND_UP(min_size, align)) {
+    if (size) *size = (size_t) p32[0];
+    if (key) *key = p32[1];
+    aligned_size = MG_ROUND_UP(p32[0] + sizeof(uint32_t) * 2, align);
+    if (left < aligned_size) aligned_size = 0;  // Out of bounds, fail
+  }
+  return aligned_size;
+}
+
+// Return the last sector of Bank 2
+static char *flash_last_sector(void) {
+  size_t ss = mg_flash_sector_size(), size = mg_flash_size();
+  char *base = (char *) mg_flash_start(), *last = base + size - ss;
+  if (mg_flash_bank() == 2) last -= size / 2;
+  return last;
+}
+
+// Find a saved object with a given key
+bool mg_flash_load(void *sector, uint32_t key, void *buf, size_t len) {
+  char *base = (char *) mg_flash_start(), *s = (char *) sector, *res = NULL;
+  size_t ss = mg_flash_sector_size(), ofs = 0, n, sz;
+  bool ok = false;
+  if (s == NULL) s = flash_last_sector();
+  if (s < base || s >= base + mg_flash_size()) {
+    MG_ERROR(("%p is outsize of flash", sector));
+  } else if (((s - base) % ss) != 0) {
+    MG_ERROR(("%p is not a sector boundary", sector));
+  } else {
+    uint32_t k, scanned = 0;
+    while ((n = mg_flash_next(s + ofs, s + ss, &k, &sz)) > 0) {
+      // MG_DEBUG((" > obj %lu, ofs %lu, key %x/%x", scanned, ofs, k, key));
+      // mg_hexdump(s + ofs, n);
+      if (k == key && sz == len) {
+        res = s + ofs + sizeof(uint32_t) * 2;
+        memcpy(buf, res, len);  // Copy object
+        ok = true;              // Keep scanning for the newer versions of it
+      }
+      ofs += n, scanned++;
+    }
+    MG_DEBUG(("Scanned %u objects, key %x is @ %p", scanned, key, res));
+  }
+  return ok;
+}
+
+static bool mg_flash_writev(char *location, struct mg_str *strings, size_t n) {
+  size_t align = mg_flash_write_align(), i, j, k = 0, nwritten = 0;
+  char buf[align];
+  bool ok = true;
+  for (i = 0; ok && i < n; i++) {
+    for (j = 0; ok && j < strings[i].len; j++) {
+      buf[k++] = strings[i].ptr[j];
+      if (k >= sizeof(buf)) {
+        ok = mg_flash_write(location + nwritten, buf, sizeof(buf));
+        k = 0, nwritten += sizeof(buf);
+      }
+    }
+  }
+  if (k > 0) {
+    while (k < sizeof(buf)) buf[k++] = 0xff;
+    ok = mg_flash_write(location + nwritten, buf, sizeof(buf));
+  }
+  return ok;
+}
+
+// For all saved objects in the sector, delete old versions of objects
+static void mg_flash_sector_cleanup(char *sector) {
+  // Buffer all saved objects into an IO buffer (backed by RAM)
+  // erase sector, and re-save them.
+  struct mg_iobuf io = {0, 0, 0, 2048};
+  size_t ss = mg_flash_sector_size();
+  size_t n, size, size2, ofs = 0, hs = sizeof(uint32_t) * 2;
+  uint32_t key;
+  // Traverse all objects
+  MG_DEBUG(("Cleaning up sector %p", sector));
+  while ((n = mg_flash_next(sector + ofs, sector + ss, &key, &size)) > 0) {
+    // Delete an old copy of this object in the cache
+    for (size_t o = 0; o < io.len; o += size2 + hs) { 
+      uint32_t k = *(uint32_t *) (io.buf + o + sizeof(uint32_t));
+      size2 = *(uint32_t *) (io.buf + o);
+      if (k == key) {
+        mg_iobuf_del(&io, o, size2 + hs);
+        break;
+      }
+    }
+    // And add the new copy
+    mg_iobuf_add(&io, io.len, sector + ofs, size + hs);  
+    ofs += n;
+  }
+  // All objects are cached in RAM now
+  if (mg_flash_erase(sector)) {  // Erase sector. If successful,
+    for (ofs = 0; ofs < io.len; ofs += size + hs) {  // Traverse cached objects
+      size = *(uint32_t *) (io.buf + ofs);
+      key = *(uint32_t *) (io.buf + ofs + sizeof(uint32_t));
+      mg_flash_save(sector, key, io.buf + ofs + hs, size);  // Save to flash
+    }
+  }
+  mg_iobuf_free(&io);
+}
+
+// Save an object with a given key - append to the end of an object list
+bool mg_flash_save(void *sector, uint32_t key, const void *buf, size_t len) {
+  char *base = (char *) mg_flash_start(), *s = (char *) sector;
+  size_t ss = mg_flash_sector_size(), ofs = 0, n;
+  bool ok = false;
+  if (s == NULL) s = flash_last_sector();
+  if (s < base || s >= base + mg_flash_size()) {
+    MG_ERROR(("%p is outsize of flash", sector));
+  } else if (((s - base) % ss) != 0) {
+    MG_ERROR(("%p is not a sector boundary", sector));
+  } else {
+    size_t needed = sizeof(uint32_t) * 2 + len;
+    size_t needed_aligned = MG_ROUND_UP(needed, mg_flash_write_align());
+    while ((n = mg_flash_next(s + ofs, s + ss, NULL, NULL)) > 0) ofs += n;
+
+    // If there is not enough space left, cleanup sector and re-eval ofs
+    if (ofs + needed_aligned > ss) {
+      mg_flash_sector_cleanup(s);
+      ofs = 0;
+      while ((n = mg_flash_next(s + ofs, s + ss, NULL, NULL)) > 0) ofs += n;
+    }
+
+    if (ofs + needed_aligned <= ss) {
+      // Enough space to save this object
+      uint32_t hdr[2] = {(uint32_t) len, key};
+      struct mg_str data[] = {mg_str_n((char *) hdr, sizeof(hdr)),
+                              mg_str_n(buf, len)};
+      ok = mg_flash_writev(s + ofs, data, 2);
+      MG_DEBUG(("Saving %lu bytes @ %p, key %x: %d", len, s + ofs, key, ok));
+      MG_DEBUG(("Sector space left: %lu bytes", ss - ofs - needed_aligned));
+    } else {
+      MG_ERROR(("Sector is full"));
+    }
+  }
+  return ok;
+}
+#else
+bool mg_flash_save(void *sector, uint32_t key, const void *buf, size_t len) {
+  (void) sector, (void) key, (void) buf, (void) len;
+  return false;
+}
+bool mg_flash_load(void *sector, uint32_t key, void *buf, size_t len) {
+  (void) sector, (void) key, (void) buf, (void) len;
+  return false;
+}
+#endif
+
+#ifdef MG_ENABLE_LINES
+#line 1 "src/device_stm32h5.c"
+#endif
+
+
+
+#if MG_DEVICE == MG_DEVICE_STM32H5
+
+#define FLASH_BASE 0x40022000          // Base address of the flash controller
+#define FLASH_KEYR (FLASH_BASE + 0x4)  // See RM0481 7.11
+#define FLASH_OPTKEYR (FLASH_BASE + 0xc)
+#define FLASH_OPTCR (FLASH_BASE + 0x1c)
+#define FLASH_NSSR (FLASH_BASE + 0x20)
+#define FLASH_NSCR (FLASH_BASE + 0x28)
+#define FLASH_NSCCR (FLASH_BASE + 0x30)
+#define FLASH_OPTSR_CUR (FLASH_BASE + 0x50)
+#define FLASH_OPTSR_PRG (FLASH_BASE + 0x54)
+
+void *mg_flash_start(void) {
+  return (void *) 0x08000000;
+}
+size_t mg_flash_size(void) {
+  return 2 * 1024 * 1024;  // 2Mb
+}
+size_t mg_flash_sector_size(void) {
+  return 8 * 1024;  // 8k
+}
+size_t mg_flash_write_align(void) {
+  return 16;  // 128 bit
+}
+int mg_flash_bank(void) {
+  return MG_REG(FLASH_OPTCR) & MG_BIT(31) ? 2 : 1;
+}
+
+static void flash_unlock(void) {
+  static bool unlocked = false;
+  if (unlocked == false) {
+    MG_REG(FLASH_KEYR) = 0x45670123;
+    MG_REG(FLASH_KEYR) = 0Xcdef89ab;
+    MG_REG(FLASH_OPTKEYR) = 0x08192a3b;
+    MG_REG(FLASH_OPTKEYR) = 0x4c5d6e7f;
+    unlocked = true;
+  }
+}
+
+static int flash_page_start(volatile uint32_t *dst) {
+  char *base = (char *) mg_flash_start(), *end = base + mg_flash_size();
+  volatile char *p = (char *) dst;
+  return p >= base && p < end && ((p - base) % mg_flash_sector_size()) == 0;
+}
+
+static bool flash_is_err(void) {
+  return MG_REG(FLASH_NSSR) & ((MG_BIT(8) - 1) << 17);  // RM0481 7.11.9
+}
+
+static void flash_wait(void) {
+  while ((MG_REG(FLASH_NSSR) & MG_BIT(0)) &&
+         (MG_REG(FLASH_NSSR) & MG_BIT(16)) == 0) {
+    (void) 0;
+  }
+}
+
+static void flash_clear_err(void) {
+  flash_wait();                                    // Wait until ready
+  MG_REG(FLASH_NSCCR) = ((MG_BIT(9) - 1) << 16U);  // Clear all errors
+}
+
+static bool flash_bank_is_swapped(void) {
+  return MG_REG(FLASH_OPTCR) & MG_BIT(31);  // RM0481 7.11.8
+}
+
+bool mg_flash_erase(void *location) {
+  bool ok = false;
+  if (flash_page_start(location) == false) {
+    MG_ERROR(("%p is not on a sector boundary"));
+  } else {
+    uintptr_t diff = (char *) location - (char *) mg_flash_start();
+    uint32_t sector = diff / mg_flash_sector_size();
+    flash_unlock();
+    flash_clear_err();
+    MG_REG(FLASH_NSCR) = 0;
+    if ((sector < 128 && flash_bank_is_swapped()) ||
+        (sector > 127 && !flash_bank_is_swapped())) {
+      MG_REG(FLASH_NSCR) |= MG_BIT(31);  // Set FLASH_CR_BKSEL
+    }
+    if (sector > 127) sector -= 128;
+    MG_REG(FLASH_NSCR) |= MG_BIT(2) | (sector << 6);  // Erase | sector_num
+    MG_REG(FLASH_NSCR) |= MG_BIT(5);                  // Start erasing
+    flash_wait();
+    ok = !flash_is_err();
+    MG_DEBUG(("Erase sector %lu @ %p: %s. CR %#lx SR %#lx", sector, location,
+              ok ? "ok" : "fail", MG_REG(FLASH_NSCR), MG_REG(FLASH_NSSR)));
+    // mg_hexdump(location, 32);
+  }
+  return ok;
+}
+
+bool mg_flash_swap_bank(void) {
+  uint32_t desired = flash_bank_is_swapped() ? 0 : MG_BIT(31);
+  flash_unlock();
+  flash_clear_err();
+  // printf("OPTSR_PRG 1 %#lx\n", FLASH->OPTSR_PRG);
+  MG_SET_BITS(MG_REG(FLASH_OPTSR_PRG), MG_BIT(31), desired);
+  // printf("OPTSR_PRG 2 %#lx\n", FLASH->OPTSR_PRG);
+  MG_REG(FLASH_OPTCR) |= MG_BIT(1);  // OPTSTART
+  while ((MG_REG(FLASH_OPTSR_CUR) & MG_BIT(31)) != desired) (void) 0;
+  return true;
+}
+
+bool mg_flash_write(void *addr, const void *buf, size_t len) {
+  if ((len % mg_flash_write_align()) != 0) {
+    MG_ERROR(("%lu is not aligned to %lu", len, mg_flash_write_align()));
+    return false;
+  }
+  uint32_t *dst = (uint32_t *) addr;
+  uint32_t *src = (uint32_t *) buf;
+  uint32_t *end = (uint32_t *) ((char *) buf + len);
+  bool ok = true;
+  flash_unlock();
+  flash_clear_err();
+  MG_ARM_DISABLE_IRQ();
+  // MG_DEBUG(("Starting flash write %lu bytes @ %p", len, addr));
+  while (ok && src < end) {
+    if (flash_page_start(dst) && mg_flash_erase(dst) == false) break;
+    MG_REG(FLASH_NSCR) = MG_BIT(1);  // Set programming flag
+    *(volatile uint32_t *) dst++ = *src++;
+    flash_wait();
+    if (flash_is_err()) ok = false;
+  }
+  MG_DEBUG(("Flash write %lu bytes @ %p: %s. CR %#lx SR %#lx", len, dst,
+            flash_is_err() ? "fail" : "ok", MG_REG(FLASH_NSCR),
+            MG_REG(FLASH_NSSR)));
+  if (flash_is_err()) ok = false;
+  // mg_hexdump(addr, len > 32 ? 32 : len);
+  //  MG_REG(FLASH_NSCR) &= ~MG_BIT(1);  // Set programming flag
+  MG_REG(FLASH_NSCR) = 0;  // Clear flags
+  MG_ARM_ENABLE_IRQ();
+  return ok;
+}
+
+void mg_device_reset(void) {
+  // SCB->AIRCR = ((0x5fa << SCB_AIRCR_VECTKEY_Pos)|SCB_AIRCR_SYSRESETREQ_Msk);
+  *(volatile unsigned long *) 0xe000ed0c = 0x5fa0004;
+}
+#endif
+
+#ifdef MG_ENABLE_LINES
+#line 1 "src/device_stm32h7.c"
+#endif
+
+
+
+#if MG_DEVICE == MG_DEVICE_STM32H7
+
+#define FLASH_BASE1 0x52002000  // Base address for bank1
+#define FLASH_BASE2 0x52002100  // Base address for bank2
+#define FLASH_KEYR 0x04         // See RM0433 4.9.2
+#define FLASH_OPTKEYR 0x08
+#define FLASH_OPTCR 0x18
+#define FLASH_SR 0x10
+#define FLASH_CR 0x0c
+#define FLASH_CCR 0x14
+#define FLASH_OPTSR_CUR 0x1c
+#define FLASH_OPTSR_PRG 0x20
+
+void *mg_flash_start(void) {
+  return (void *) 0x08000000;
+}
+size_t mg_flash_size(void) {
+  return 2 * 1024 * 1024;  // 2Mb
+}
+size_t mg_flash_sector_size(void) {
+  return 128 * 1024;  // 128k
+}
+size_t mg_flash_write_align(void) {
+  return 32;  // 256 bit
+}
+int mg_flash_bank(void) {
+  return MG_REG(FLASH_BASE1 + FLASH_OPTCR) & MG_BIT(31) ? 2 : 1;
+}
+
+static void flash_unlock(void) {
+  static bool unlocked = false;
+  if (unlocked == false) {
+    MG_REG(FLASH_BASE1 + FLASH_KEYR) = 0x45670123;
+    MG_REG(FLASH_BASE1 + FLASH_KEYR) = 0xcdef89ab;
+    MG_REG(FLASH_BASE2 + FLASH_KEYR) = 0x45670123;
+    MG_REG(FLASH_BASE2 + FLASH_KEYR) = 0xcdef89ab;
+    MG_REG(FLASH_BASE1 + FLASH_OPTKEYR) = 0x08192a3b;  // opt reg is "shared"
+    MG_REG(FLASH_BASE1 + FLASH_OPTKEYR) = 0x4c5d6e7f;  // thus unlock once
+    unlocked = true;
+  }
+}
+
+static bool flash_page_start(volatile uint32_t *dst) {
+  char *base = (char *) mg_flash_start(), *end = base + mg_flash_size();
+  volatile char *p = (char *) dst;
+  return p >= base && p < end && ((p - base) % mg_flash_sector_size()) == 0;
+}
+
+static bool flash_is_err(uint32_t bank) {
+  return MG_REG(bank + FLASH_SR) & ((MG_BIT(11) - 1) << 17);  // RM0433 4.9.5
+}
+
+static void flash_wait(uint32_t bank) {
+  while (MG_REG(bank + FLASH_SR) & (MG_BIT(0) | MG_BIT(2))) (void) 0;
+}
+
+static void flash_clear_err(uint32_t bank) {
+  flash_wait(bank);                                      // Wait until ready
+  MG_REG(bank + FLASH_CCR) = ((MG_BIT(11) - 1) << 16U);  // Clear all errors
+}
+
+static bool flash_bank_is_swapped(uint32_t bank) {
+  return MG_REG(bank + FLASH_OPTCR) & MG_BIT(31);  // RM0433 4.9.7
+}
+
+// Figure out flash bank based on the address
+static uint32_t flash_bank(void *addr) {
+  size_t ofs = (char *) addr - (char *) mg_flash_start();
+  return ofs < mg_flash_size() / 2 ? FLASH_BASE1 : FLASH_BASE2;
+}
+
+bool mg_flash_erase(void *addr) {
+  bool ok = false;
+  if (flash_page_start(addr) == false) {
+    MG_ERROR(("%p is not on a sector boundary", addr));
+  } else {
+    uintptr_t diff = (char *) addr - (char *) mg_flash_start();
+    uint32_t sector = diff / mg_flash_sector_size();
+    uint32_t bank = flash_bank(addr);
+
+    flash_unlock();
+    if (sector > 7) sector -= 8;
+    // MG_INFO(("Erasing @ %p, sector %lu, bank %#x", addr, sector, bank));
+
+    flash_clear_err(bank);
+    MG_REG(bank + FLASH_CR) |= (sector & 7U) << 8U;  // Sector to erase
+    MG_REG(bank + FLASH_CR) |= MG_BIT(2);            // Sector erase bit
+    MG_REG(bank + FLASH_CR) |= MG_BIT(7);            // Start erasing
+    ok = !flash_is_err(bank);
+    MG_DEBUG(("Erase sector %lu @ %p %s. CR %#lx SR %#lx", sector, addr,
+              ok ? "ok" : "fail", MG_REG(bank + FLASH_CR),
+              MG_REG(bank + FLASH_SR)));
+    // mg_hexdump(addr, 32);
+  }
+  return ok;
+}
+
+bool mg_flash_swap_bank() {
+  uint32_t bank = FLASH_BASE1;
+  uint32_t desired = flash_bank_is_swapped(bank) ? 0 : MG_BIT(31);
+  flash_unlock();
+  flash_clear_err(bank);
+  // printf("OPTSR_PRG 1 %#lx\n", FLASH->OPTSR_PRG);
+  MG_SET_BITS(MG_REG(bank + FLASH_OPTSR_PRG), MG_BIT(31), desired);
+  // printf("OPTSR_PRG 2 %#lx\n", FLASH->OPTSR_PRG);
+  MG_REG(bank + FLASH_OPTCR) |= MG_BIT(1);  // OPTSTART
+  while ((MG_REG(bank + FLASH_OPTSR_CUR) & MG_BIT(31)) != desired) (void) 0;
+  return true;
+}
+
+bool mg_flash_write(void *addr, const void *buf, size_t len) {
+  if ((len % mg_flash_write_align()) != 0) {
+    MG_ERROR(("%lu is not aligned to %lu", len, mg_flash_write_align()));
+    return false;
+  }
+  uint32_t bank = flash_bank(addr);
+  uint32_t *dst = (uint32_t *) addr;
+  uint32_t *src = (uint32_t *) buf;
+  uint32_t *end = (uint32_t *) ((char *) buf + len);
+  bool ok = true;
+  flash_unlock();
+  flash_clear_err(bank);
+  MG_ARM_DISABLE_IRQ();
+  MG_REG(bank + FLASH_CR) = MG_BIT(1);  // Set programming flag
+  // MG_INFO(("Writing flash @ %p, %lu bytes", addr, len));
+  while (ok && src < end) {
+    if (flash_page_start(dst) && mg_flash_erase(dst) == false) break;
+    *(volatile uint32_t *) dst++ = *src++;
+    flash_wait(bank);
+    if (flash_is_err(bank)) ok = false;
+  }
+  MG_DEBUG(("Flash write %lu bytes @ %p: %s. CR %#lx SR %#lx", len, dst,
+            ok ? "ok" : "fail", MG_REG(bank + FLASH_CR),
+            MG_REG(bank + FLASH_SR)));
+  // mg_hexdump(addr, len > 32 ? 32 : len);
+  MG_REG(bank + FLASH_CR) &= ~MG_BIT(1);  // Clear programming flag
+  MG_ARM_ENABLE_IRQ();
+  return ok;
+}
+
+void mg_device_reset(void) {
+  // SCB->AIRCR = ((0x5fa << SCB_AIRCR_VECTKEY_Pos)|SCB_AIRCR_SYSRESETREQ_Msk);
+  *(volatile unsigned long *) 0xe000ed0c = 0x5fa0004;
+}
+#endif
+
 #ifdef MG_ENABLE_LINES
 #line 1 "src/dns.c"
 #endif
@@ -4989,7 +5488,7 @@ size_t mg_ota_size(int fw) {
 
 
 
-// This OTA implementation uses the internal flash API outlined in sys.h
+// This OTA implementation uses the internal flash API outlined in device.h
 // It splits flash into 2 equal partitions, and stores OTA status in the
 // last sector of the partition.
 
@@ -6693,505 +7192,6 @@ bool mg_path_is_sane(const char *path) {
   return true;
 }
 
-#ifdef MG_ENABLE_LINES
-#line 1 "src/sys_dummy.c"
-#endif
-
-
-#if MG_SYS == MG_SYS_NONE
-void *mg_flash_start(void) {
-  return NULL;
-}
-size_t mg_flash_size(void) {
-  return 0;
-}
-size_t mg_flash_sector_size(void) {
-  return 0;
-}
-size_t mg_flash_write_align(void) {
-  return 0;
-}
-int mg_flash_bank(void) {
-  return 0;
-}
-bool mg_flash_erase(void *location) {
-  (void) location;
-  return false;
-}
-bool mg_flash_swap_bank(void) {
-  return true;
-}
-bool mg_flash_write(void *addr, const void *buf, size_t len) {
-  (void) addr, (void) buf, (void) len;
-  return false;
-}
-void mg_sys_reset(void) {
-}
-#endif
-
-#ifdef MG_ENABLE_LINES
-#line 1 "src/sys_flash.c"
-#endif
-
-
-#if MG_SYS == MG_SYS_STM32H7 || MG_SYS == MG_SYS_STM32H5
-// Flash can be written only if it is erased. Erased flash is 0xff (all bits 1)
-// Writes must be mg_flash_write_align() - aligned. Thus if we want to save an
-// object, we pad it at the end for alignment.
-//
-// Objects in the flash sector are stored sequentially:
-// | 32-bit size | 32-bit KEY | ..data.. | ..pad.. | 32-bit size | ......
-//
-// In order to get to the next object, read its size, then align up.
-
-// Traverse the list of saved objects
-size_t mg_flash_next(char *p, char *end, uint32_t *key, size_t *size) {
-  size_t aligned_size = 0, align = mg_flash_write_align(), left = end - p;
-  uint32_t *p32 = (uint32_t *) p, min_size = sizeof(uint32_t) * 2;
-  if (p32[0] != 0xffffffff && left > MG_ROUND_UP(min_size, align)) {
-    if (size) *size = (size_t) p32[0];
-    if (key) *key = p32[1];
-    aligned_size = MG_ROUND_UP(p32[0] + sizeof(uint32_t) * 2, align);
-    if (left < aligned_size) aligned_size = 0;  // Out of bounds, fail
-  }
-  return aligned_size;
-}
-
-// Return the last sector of Bank 2
-static char *flash_last_sector(void) {
-  size_t ss = mg_flash_sector_size(), size = mg_flash_size();
-  char *base = (char *) mg_flash_start(), *last = base + size - ss;
-  if (mg_flash_bank() == 2) last -= size / 2;
-  return last;
-}
-
-// Find a saved object with a given key
-bool mg_flash_load(void *sector, uint32_t key, void *buf, size_t len) {
-  char *base = (char *) mg_flash_start(), *s = (char *) sector, *res = NULL;
-  size_t ss = mg_flash_sector_size(), ofs = 0, n, sz;
-  bool ok = false;
-  if (s == NULL) s = flash_last_sector();
-  if (s < base || s >= base + mg_flash_size()) {
-    MG_ERROR(("%p is outsize of flash", sector));
-  } else if (((s - base) % ss) != 0) {
-    MG_ERROR(("%p is not a sector boundary", sector));
-  } else {
-    uint32_t k, scanned = 0;
-    while ((n = mg_flash_next(s + ofs, s + ss, &k, &sz)) > 0) {
-      // MG_DEBUG((" > obj %lu, ofs %lu, key %x/%x", scanned, ofs, k, key));
-      // mg_hexdump(s + ofs, n);
-      if (k == key && sz == len) {
-        res = s + ofs + sizeof(uint32_t) * 2;
-        memcpy(buf, res, len);  // Copy object
-        ok = true;              // Keep scanning for the newer versions of it
-      }
-      ofs += n, scanned++;
-    }
-    MG_DEBUG(("Scanned %u objects, key %x is @ %p", scanned, key, res));
-  }
-  return ok;
-}
-
-static bool mg_flash_writev(char *location, struct mg_str *strings, size_t n) {
-  size_t align = mg_flash_write_align(), i, j, k = 0, nwritten = 0;
-  char buf[align];
-  bool ok = true;
-  for (i = 0; ok && i < n; i++) {
-    for (j = 0; ok && j < strings[i].len; j++) {
-      buf[k++] = strings[i].ptr[j];
-      if (k >= sizeof(buf)) {
-        ok = mg_flash_write(location + nwritten, buf, sizeof(buf));
-        k = 0, nwritten += sizeof(buf);
-      }
-    }
-  }
-  if (k > 0) {
-    while (k < sizeof(buf)) buf[k++] = 0xff;
-    ok = mg_flash_write(location + nwritten, buf, sizeof(buf));
-  }
-  return ok;
-}
-
-// For all saved objects in the sector, delete old versions of objects
-static void mg_flash_sector_cleanup(char *sector) {
-  // Buffer all saved objects into an IO buffer (backed by RAM)
-  // erase sector, and re-save them.
-  struct mg_iobuf io = {0, 0, 0, 2048};
-  size_t ss = mg_flash_sector_size();
-  size_t n, size, size2, ofs = 0, hs = sizeof(uint32_t) * 2;
-  uint32_t key;
-  // Traverse all objects
-  MG_DEBUG(("Cleaning up sector %p", sector));
-  while ((n = mg_flash_next(sector + ofs, sector + ss, &key, &size)) > 0) {
-    // Delete an old copy of this object in the cache
-    for (size_t o = 0; o < io.len; o += size2 + hs) { 
-      uint32_t k = *(uint32_t *) (io.buf + o + sizeof(uint32_t));
-      size2 = *(uint32_t *) (io.buf + o);
-      if (k == key) {
-        mg_iobuf_del(&io, o, size2 + hs);
-        break;
-      }
-    }
-    // And add the new copy
-    mg_iobuf_add(&io, io.len, sector + ofs, size + hs);  
-    ofs += n;
-  }
-  // All objects are cached in RAM now
-  if (mg_flash_erase(sector)) {  // Erase sector. If successful,
-    for (ofs = 0; ofs < io.len; ofs += size + hs) {  // Traverse cached objects
-      size = *(uint32_t *) (io.buf + ofs);
-      key = *(uint32_t *) (io.buf + ofs + sizeof(uint32_t));
-      mg_flash_save(sector, key, io.buf + ofs + hs, size);  // Save to flash
-    }
-  }
-  mg_iobuf_free(&io);
-}
-
-// Save an object with a given key - append to the end of an object list
-bool mg_flash_save(void *sector, uint32_t key, const void *buf, size_t len) {
-  char *base = (char *) mg_flash_start(), *s = (char *) sector;
-  size_t ss = mg_flash_sector_size(), ofs = 0, n;
-  bool ok = false;
-  if (s == NULL) s = flash_last_sector();
-  if (s < base || s >= base + mg_flash_size()) {
-    MG_ERROR(("%p is outsize of flash", sector));
-  } else if (((s - base) % ss) != 0) {
-    MG_ERROR(("%p is not a sector boundary", sector));
-  } else {
-    size_t needed = sizeof(uint32_t) * 2 + len;
-    size_t needed_aligned = MG_ROUND_UP(needed, mg_flash_write_align());
-    while ((n = mg_flash_next(s + ofs, s + ss, NULL, NULL)) > 0) ofs += n;
-
-    // If there is not enough space left, cleanup sector and re-eval ofs
-    if (ofs + needed_aligned > ss) {
-      mg_flash_sector_cleanup(s);
-      ofs = 0;
-      while ((n = mg_flash_next(s + ofs, s + ss, NULL, NULL)) > 0) ofs += n;
-    }
-
-    if (ofs + needed_aligned <= ss) {
-      // Enough space to save this object
-      uint32_t hdr[2] = {(uint32_t) len, key};
-      struct mg_str data[] = {mg_str_n((char *) hdr, sizeof(hdr)),
-                              mg_str_n(buf, len)};
-      ok = mg_flash_writev(s + ofs, data, 2);
-      MG_DEBUG(("Saving %lu bytes @ %p, key %x: %d", len, s + ofs, key, ok));
-      MG_DEBUG(("Sector space left: %lu bytes", ss - ofs - needed_aligned));
-    } else {
-      MG_ERROR(("Sector is full"));
-    }
-  }
-  return ok;
-}
-#else
-bool mg_flash_save(void *sector, uint32_t key, const void *buf, size_t len) {
-  (void) sector, (void) key, (void) buf, (void) len;
-  return false;
-}
-bool mg_flash_load(void *sector, uint32_t key, void *buf, size_t len) {
-  (void) sector, (void) key, (void) buf, (void) len;
-  return false;
-}
-#endif
-
-#ifdef MG_ENABLE_LINES
-#line 1 "src/sys_stm32h5.c"
-#endif
-
-
-
-#if MG_SYS == MG_SYS_STM32H5
-
-#define FLASH_BASE 0x40022000          // Base address of the flash controller
-#define FLASH_KEYR (FLASH_BASE + 0x4)  // See RM0481 7.11
-#define FLASH_OPTKEYR (FLASH_BASE + 0xc)
-#define FLASH_OPTCR (FLASH_BASE + 0x1c)
-#define FLASH_NSSR (FLASH_BASE + 0x20)
-#define FLASH_NSCR (FLASH_BASE + 0x28)
-#define FLASH_NSCCR (FLASH_BASE + 0x30)
-#define FLASH_OPTSR_CUR (FLASH_BASE + 0x50)
-#define FLASH_OPTSR_PRG (FLASH_BASE + 0x54)
-
-void *mg_flash_start(void) {
-  return (void *) 0x08000000;
-}
-size_t mg_flash_size(void) {
-  return 2 * 1024 * 1024;  // 2Mb
-}
-size_t mg_flash_sector_size(void) {
-  return 8 * 1024;  // 8k
-}
-size_t mg_flash_write_align(void) {
-  return 16;  // 128 bit
-}
-int mg_flash_bank(void) {
-  return MG_REG(FLASH_OPTCR) & MG_BIT(31) ? 2 : 1;
-}
-
-static void flash_unlock(void) {
-  static bool unlocked = false;
-  if (unlocked == false) {
-    MG_REG(FLASH_KEYR) = 0x45670123;
-    MG_REG(FLASH_KEYR) = 0Xcdef89ab;
-    MG_REG(FLASH_OPTKEYR) = 0x08192a3b;
-    MG_REG(FLASH_OPTKEYR) = 0x4c5d6e7f;
-    unlocked = true;
-  }
-}
-
-static int flash_page_start(volatile uint32_t *dst) {
-  char *base = (char *) mg_flash_start(), *end = base + mg_flash_size();
-  volatile char *p = (char *) dst;
-  return p >= base && p < end && ((p - base) % mg_flash_sector_size()) == 0;
-}
-
-static bool flash_is_err(void) {
-  return MG_REG(FLASH_NSSR) & ((MG_BIT(8) - 1) << 17);  // RM0481 7.11.9
-}
-
-static void flash_wait(void) {
-  while ((MG_REG(FLASH_NSSR) & MG_BIT(0)) &&
-         (MG_REG(FLASH_NSSR) & MG_BIT(16)) == 0) {
-    (void) 0;
-  }
-}
-
-static void flash_clear_err(void) {
-  flash_wait();                                    // Wait until ready
-  MG_REG(FLASH_NSCCR) = ((MG_BIT(9) - 1) << 16U);  // Clear all errors
-}
-
-static bool flash_bank_is_swapped(void) {
-  return MG_REG(FLASH_OPTCR) & MG_BIT(31);  // RM0481 7.11.8
-}
-
-bool mg_flash_erase(void *location) {
-  bool ok = false;
-  if (flash_page_start(location) == false) {
-    MG_ERROR(("%p is not on a sector boundary"));
-  } else {
-    uintptr_t diff = (char *) location - (char *) mg_flash_start();
-    uint32_t sector = diff / mg_flash_sector_size();
-    flash_unlock();
-    flash_clear_err();
-    MG_REG(FLASH_NSCR) = 0;
-    if ((sector < 128 && flash_bank_is_swapped()) ||
-        (sector > 127 && !flash_bank_is_swapped())) {
-      MG_REG(FLASH_NSCR) |= MG_BIT(31);  // Set FLASH_CR_BKSEL
-    }
-    if (sector > 127) sector -= 128;
-    MG_REG(FLASH_NSCR) |= MG_BIT(2) | (sector << 6);  // Erase | sector_num
-    MG_REG(FLASH_NSCR) |= MG_BIT(5);                  // Start erasing
-    flash_wait();
-    ok = !flash_is_err();
-    MG_DEBUG(("Erase sector %lu @ %p: %s. CR %#lx SR %#lx", sector, location,
-              ok ? "ok" : "fail", MG_REG(FLASH_NSCR), MG_REG(FLASH_NSSR)));
-    // mg_hexdump(location, 32);
-  }
-  return ok;
-}
-
-bool mg_flash_swap_bank(void) {
-  uint32_t desired = flash_bank_is_swapped() ? 0 : MG_BIT(31);
-  flash_unlock();
-  flash_clear_err();
-  // printf("OPTSR_PRG 1 %#lx\n", FLASH->OPTSR_PRG);
-  MG_SET_BITS(MG_REG(FLASH_OPTSR_PRG), MG_BIT(31), desired);
-  // printf("OPTSR_PRG 2 %#lx\n", FLASH->OPTSR_PRG);
-  MG_REG(FLASH_OPTCR) |= MG_BIT(1);  // OPTSTART
-  while ((MG_REG(FLASH_OPTSR_CUR) & MG_BIT(31)) != desired) (void) 0;
-  return true;
-}
-
-bool mg_flash_write(void *addr, const void *buf, size_t len) {
-  if ((len % mg_flash_write_align()) != 0) {
-    MG_ERROR(("%lu is not aligned to %lu", len, mg_flash_write_align()));
-    return false;
-  }
-  uint32_t *dst = (uint32_t *) addr;
-  uint32_t *src = (uint32_t *) buf;
-  uint32_t *end = (uint32_t *) ((char *) buf + len);
-  bool ok = true;
-  flash_unlock();
-  flash_clear_err();
-  MG_ARM_DISABLE_IRQ();
-  // MG_DEBUG(("Starting flash write %lu bytes @ %p", len, addr));
-  while (ok && src < end) {
-    if (flash_page_start(dst) && mg_flash_erase(dst) == false) break;
-    MG_REG(FLASH_NSCR) = MG_BIT(1);  // Set programming flag
-    *(volatile uint32_t *) dst++ = *src++;
-    flash_wait();
-    if (flash_is_err()) ok = false;
-  }
-  MG_DEBUG(("Flash write %lu bytes @ %p: %s. CR %#lx SR %#lx", len, dst,
-            flash_is_err() ? "fail" : "ok", MG_REG(FLASH_NSCR),
-            MG_REG(FLASH_NSSR)));
-  if (flash_is_err()) ok = false;
-  // mg_hexdump(addr, len > 32 ? 32 : len);
-  //  MG_REG(FLASH_NSCR) &= ~MG_BIT(1);  // Set programming flag
-  MG_REG(FLASH_NSCR) = 0;  // Clear flags
-  MG_ARM_ENABLE_IRQ();
-  return ok;
-}
-
-void mg_sys_reset(void) {
-  // SCB->AIRCR = ((0x5fa << SCB_AIRCR_VECTKEY_Pos)|SCB_AIRCR_SYSRESETREQ_Msk);
-  *(volatile unsigned long *) 0xe000ed0c = 0x5fa0004;
-}
-#endif
-
-#ifdef MG_ENABLE_LINES
-#line 1 "src/sys_stm32h7.c"
-#endif
-
-
-
-#if MG_SYS == MG_SYS_STM32H7
-
-#define FLASH_BASE1 0x52002000  // Base address for bank1
-#define FLASH_BASE2 0x52002100  // Base address for bank2
-#define FLASH_KEYR 0x04         // See RM0433 4.9.2
-#define FLASH_OPTKEYR 0x08
-#define FLASH_OPTCR 0x18
-#define FLASH_SR 0x10
-#define FLASH_CR 0x0c
-#define FLASH_CCR 0x14
-#define FLASH_OPTSR_CUR 0x1c
-#define FLASH_OPTSR_PRG 0x20
-
-void *mg_flash_start(void) {
-  return (void *) 0x08000000;
-}
-size_t mg_flash_size(void) {
-  return 2 * 1024 * 1024;  // 2Mb
-}
-size_t mg_flash_sector_size(void) {
-  return 128 * 1024;  // 128k
-}
-size_t mg_flash_write_align(void) {
-  return 32;  // 256 bit
-}
-int mg_flash_bank(void) {
-  return MG_REG(FLASH_BASE1 + FLASH_OPTCR) & MG_BIT(31) ? 2 : 1;
-}
-
-static void flash_unlock(void) {
-  static bool unlocked = false;
-  if (unlocked == false) {
-    MG_REG(FLASH_BASE1 + FLASH_KEYR) = 0x45670123;
-    MG_REG(FLASH_BASE1 + FLASH_KEYR) = 0xcdef89ab;
-    MG_REG(FLASH_BASE2 + FLASH_KEYR) = 0x45670123;
-    MG_REG(FLASH_BASE2 + FLASH_KEYR) = 0xcdef89ab;
-    MG_REG(FLASH_BASE1 + FLASH_OPTKEYR) = 0x08192a3b;  // opt reg is "shared"
-    MG_REG(FLASH_BASE1 + FLASH_OPTKEYR) = 0x4c5d6e7f;  // thus unlock once
-    unlocked = true;
-  }
-}
-
-static bool flash_page_start(volatile uint32_t *dst) {
-  char *base = (char *) mg_flash_start(), *end = base + mg_flash_size();
-  volatile char *p = (char *) dst;
-  return p >= base && p < end && ((p - base) % mg_flash_sector_size()) == 0;
-}
-
-static bool flash_is_err(uint32_t bank) {
-  return MG_REG(bank + FLASH_SR) & ((MG_BIT(11) - 1) << 17);  // RM0433 4.9.5
-}
-
-static void flash_wait(uint32_t bank) {
-  while (MG_REG(bank + FLASH_SR) & (MG_BIT(0) | MG_BIT(2))) (void) 0;
-}
-
-static void flash_clear_err(uint32_t bank) {
-  flash_wait(bank);                                      // Wait until ready
-  MG_REG(bank + FLASH_CCR) = ((MG_BIT(11) - 1) << 16U);  // Clear all errors
-}
-
-static bool flash_bank_is_swapped(uint32_t bank) {
-  return MG_REG(bank + FLASH_OPTCR) & MG_BIT(31);  // RM0433 4.9.7
-}
-
-// Figure out flash bank based on the address
-static uint32_t flash_bank(void *addr) {
-  size_t ofs = (char *) addr - (char *) mg_flash_start();
-  return ofs < mg_flash_size() / 2 ? FLASH_BASE1 : FLASH_BASE2;
-}
-
-bool mg_flash_erase(void *addr) {
-  bool ok = false;
-  if (flash_page_start(addr) == false) {
-    MG_ERROR(("%p is not on a sector boundary", addr));
-  } else {
-    uintptr_t diff = (char *) addr - (char *) mg_flash_start();
-    uint32_t sector = diff / mg_flash_sector_size();
-    uint32_t bank = flash_bank(addr);
-
-    flash_unlock();
-    if (sector > 7) sector -= 8;
-    // MG_INFO(("Erasing @ %p, sector %lu, bank %#x", addr, sector, bank));
-
-    flash_clear_err(bank);
-    MG_REG(bank + FLASH_CR) |= (sector & 7U) << 8U;  // Sector to erase
-    MG_REG(bank + FLASH_CR) |= MG_BIT(2);            // Sector erase bit
-    MG_REG(bank + FLASH_CR) |= MG_BIT(7);            // Start erasing
-    ok = !flash_is_err(bank);
-    MG_DEBUG(("Erase sector %lu @ %p %s. CR %#lx SR %#lx", sector, addr,
-              ok ? "ok" : "fail", MG_REG(bank + FLASH_CR),
-              MG_REG(bank + FLASH_SR)));
-    // mg_hexdump(addr, 32);
-  }
-  return ok;
-}
-
-bool mg_flash_swap_bank() {
-  uint32_t bank = FLASH_BASE1;
-  uint32_t desired = flash_bank_is_swapped(bank) ? 0 : MG_BIT(31);
-  flash_unlock();
-  flash_clear_err(bank);
-  // printf("OPTSR_PRG 1 %#lx\n", FLASH->OPTSR_PRG);
-  MG_SET_BITS(MG_REG(bank + FLASH_OPTSR_PRG), MG_BIT(31), desired);
-  // printf("OPTSR_PRG 2 %#lx\n", FLASH->OPTSR_PRG);
-  MG_REG(bank + FLASH_OPTCR) |= MG_BIT(1);  // OPTSTART
-  while ((MG_REG(bank + FLASH_OPTSR_CUR) & MG_BIT(31)) != desired) (void) 0;
-  return true;
-}
-
-bool mg_flash_write(void *addr, const void *buf, size_t len) {
-  if ((len % mg_flash_write_align()) != 0) {
-    MG_ERROR(("%lu is not aligned to %lu", len, mg_flash_write_align()));
-    return false;
-  }
-  uint32_t bank = flash_bank(addr);
-  uint32_t *dst = (uint32_t *) addr;
-  uint32_t *src = (uint32_t *) buf;
-  uint32_t *end = (uint32_t *) ((char *) buf + len);
-  bool ok = true;
-  flash_unlock();
-  flash_clear_err(bank);
-  MG_ARM_DISABLE_IRQ();
-  MG_REG(bank + FLASH_CR) = MG_BIT(1);  // Set programming flag
-  // MG_INFO(("Writing flash @ %p, %lu bytes", addr, len));
-  while (ok && src < end) {
-    if (flash_page_start(dst) && mg_flash_erase(dst) == false) break;
-    *(volatile uint32_t *) dst++ = *src++;
-    flash_wait(bank);
-    if (flash_is_err(bank)) ok = false;
-  }
-  MG_DEBUG(("Flash write %lu bytes @ %p: %s. CR %#lx SR %#lx", len, dst,
-            ok ? "ok" : "fail", MG_REG(bank + FLASH_CR),
-            MG_REG(bank + FLASH_SR)));
-  // mg_hexdump(addr, len > 32 ? 32 : len);
-  MG_REG(bank + FLASH_CR) &= ~MG_BIT(1);  // Clear programming flag
-  MG_ARM_ENABLE_IRQ();
-  return ok;
-}
-
-void mg_sys_reset(void) {
-  // SCB->AIRCR = ((0x5fa << SCB_AIRCR_VECTKEY_Pos)|SCB_AIRCR_SYSRESETREQ_Msk);
-  *(volatile unsigned long *) 0xe000ed0c = 0x5fa0004;
-}
-#endif
-
 #ifdef MG_ENABLE_LINES
 #line 1 "src/timer.c"
 #endif
diff --git a/mongoose.h b/mongoose.h
index 7fb5fb9b..de7debda 100644
--- a/mongoose.h
+++ b/mongoose.h
@@ -1701,13 +1701,13 @@ bool mg_ota_rollback(void);  // Rollback to the previous firmware
 
 
 
-#define MG_SYS_NONE 0      // Dummy system
-#define MG_SYS_STM32H5 1   // STM32 H5
-#define MG_SYS_STM32H7 2   // STM32 H7
-#define MG_SYS_CUSTOM 100  // Custom implementation
+#define MG_DEVICE_NONE 0      // Dummy system
+#define MG_DEVICE_STM32H5 1   // STM32 H5
+#define MG_DEVICE_STM32H7 2   // STM32 H7
+#define MG_DEVICE_CUSTOM 100  // Custom implementation
 
-#ifndef MG_SYS
-#define MG_SYS MG_SYS_NONE
+#ifndef MG_DEVICE
+#define MG_DEVICE MG_DEVICE_NONE
 #endif
 
 // Flash information
@@ -1727,7 +1727,7 @@ bool mg_flash_swap_bank(void);
 bool mg_flash_load(void *sector, uint32_t key, void *buf, size_t len);
 bool mg_flash_save(void *sector, uint32_t key, const void *buf, size_t len);
 
-void mg_sys_reset(void);  // Reboot device immediately
+void mg_device_reset(void);  // Reboot device immediately
 
 
 
diff --git a/src/sys.h b/src/device.h
similarity index 76%
rename from src/sys.h
rename to src/device.h
index f384a488..d73397e4 100644
--- a/src/sys.h
+++ b/src/device.h
@@ -5,13 +5,13 @@
 
 #include "arch.h"
 
-#define MG_SYS_NONE 0      // Dummy system
-#define MG_SYS_STM32H5 1   // STM32 H5
-#define MG_SYS_STM32H7 2   // STM32 H7
-#define MG_SYS_CUSTOM 100  // Custom implementation
+#define MG_DEVICE_NONE 0      // Dummy system
+#define MG_DEVICE_STM32H5 1   // STM32 H5
+#define MG_DEVICE_STM32H7 2   // STM32 H7
+#define MG_DEVICE_CUSTOM 100  // Custom implementation
 
-#ifndef MG_SYS
-#define MG_SYS MG_SYS_NONE
+#ifndef MG_DEVICE
+#define MG_DEVICE MG_DEVICE_NONE
 #endif
 
 // Flash information
@@ -31,4 +31,4 @@ bool mg_flash_swap_bank(void);
 bool mg_flash_load(void *sector, uint32_t key, void *buf, size_t len);
 bool mg_flash_save(void *sector, uint32_t key, const void *buf, size_t len);
 
-void mg_sys_reset(void);  // Reboot device immediately
+void mg_device_reset(void);  // Reboot device immediately
diff --git a/src/sys_dummy.c b/src/device_dummy.c
similarity index 85%
rename from src/sys_dummy.c
rename to src/device_dummy.c
index 80834e6e..8eb5a759 100644
--- a/src/sys_dummy.c
+++ b/src/device_dummy.c
@@ -1,6 +1,6 @@
-#include "sys.h"
+#include "device.h"
 
-#if MG_SYS == MG_SYS_NONE
+#if MG_DEVICE == MG_DEVICE_NONE
 void *mg_flash_start(void) {
   return NULL;
 }
@@ -27,6 +27,6 @@ bool mg_flash_write(void *addr, const void *buf, size_t len) {
   (void) addr, (void) buf, (void) len;
   return false;
 }
-void mg_sys_reset(void) {
+void mg_device_reset(void) {
 }
 #endif
diff --git a/src/sys_flash.c b/src/device_flash.c
similarity index 98%
rename from src/sys_flash.c
rename to src/device_flash.c
index a764a5d9..70d759af 100644
--- a/src/sys_flash.c
+++ b/src/device_flash.c
@@ -1,6 +1,6 @@
-#include "sys.h"
+#include "device.h"
 
-#if MG_SYS == MG_SYS_STM32H7 || MG_SYS == MG_SYS_STM32H5
+#if MG_DEVICE == MG_DEVICE_STM32H7 || MG_DEVICE == MG_DEVICE_STM32H5
 // Flash can be written only if it is erased. Erased flash is 0xff (all bits 1)
 // Writes must be mg_flash_write_align() - aligned. Thus if we want to save an
 // object, we pad it at the end for alignment.
diff --git a/src/sys_stm32h5.c b/src/device_stm32h5.c
similarity index 98%
rename from src/sys_stm32h5.c
rename to src/device_stm32h5.c
index eaa74b74..e4c5d332 100644
--- a/src/sys_stm32h5.c
+++ b/src/device_stm32h5.c
@@ -1,7 +1,7 @@
 #include "log.h"
-#include "sys.h"
+#include "device.h"
 
-#if MG_SYS == MG_SYS_STM32H5
+#if MG_DEVICE == MG_DEVICE_STM32H5
 
 #define FLASH_BASE 0x40022000          // Base address of the flash controller
 #define FLASH_KEYR (FLASH_BASE + 0x4)  // See RM0481 7.11
@@ -135,7 +135,7 @@ bool mg_flash_write(void *addr, const void *buf, size_t len) {
   return ok;
 }
 
-void mg_sys_reset(void) {
+void mg_device_reset(void) {
   // SCB->AIRCR = ((0x5fa << SCB_AIRCR_VECTKEY_Pos)|SCB_AIRCR_SYSRESETREQ_Msk);
   *(volatile unsigned long *) 0xe000ed0c = 0x5fa0004;
 }
diff --git a/src/sys_stm32h7.c b/src/device_stm32h7.c
similarity index 98%
rename from src/sys_stm32h7.c
rename to src/device_stm32h7.c
index ae3b93e9..b33ca15d 100644
--- a/src/sys_stm32h7.c
+++ b/src/device_stm32h7.c
@@ -1,7 +1,7 @@
 #include "log.h"
-#include "sys.h"
+#include "device.h"
 
-#if MG_SYS == MG_SYS_STM32H7
+#if MG_DEVICE == MG_DEVICE_STM32H7
 
 #define FLASH_BASE1 0x52002000  // Base address for bank1
 #define FLASH_BASE2 0x52002100  // Base address for bank2
@@ -141,7 +141,7 @@ bool mg_flash_write(void *addr, const void *buf, size_t len) {
   return ok;
 }
 
-void mg_sys_reset(void) {
+void mg_device_reset(void) {
   // SCB->AIRCR = ((0x5fa << SCB_AIRCR_VECTKEY_Pos)|SCB_AIRCR_SYSRESETREQ_Msk);
   *(volatile unsigned long *) 0xe000ed0c = 0x5fa0004;
 }
diff --git a/src/ota_flash.c b/src/ota_flash.c
index 5e4e5490..da10757a 100644
--- a/src/ota_flash.c
+++ b/src/ota_flash.c
@@ -1,9 +1,9 @@
 #include "arch.h"
 #include "log.h"
 #include "ota.h"
-#include "sys.h"
+#include "device.h"
 
-// This OTA implementation uses the internal flash API outlined in sys.h
+// This OTA implementation uses the internal flash API outlined in device.h
 // It splits flash into 2 equal partitions, and stores OTA status in the
 // last sector of the partition.