got code working to download each piece of the cape code separately
diff --git a/bbb_cape/src/flasher/stm32_flasher.cc b/bbb_cape/src/flasher/stm32_flasher.cc
new file mode 100644
index 0000000..68efd0e
--- /dev/null
+++ b/bbb_cape/src/flasher/stm32_flasher.cc
@@ -0,0 +1,186 @@
+#include <libgen.h>
+#include <string.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <fcntl.h>
+
+#include <string>
+
+#include "aos/common/logging/logging.h"
+#include "aos/common/logging/logging_impl.h"
+
+extern "C" {
+#include "stm32flash/parsers/parser.h"
+#include "stm32flash/parsers/hex.h"
+#include "stm32flash/serial.h"
+#include "stm32flash/stm32.h"
+#include "stm32flash/init.h"
+}
+
+int main(int argc, char **argv) {
+  ::aos::logging::Init();
+
+  if (argc < 2) {
+    fputs("Need an argument saying which target to download.\n", stderr);
+    return 1;
+  }
+  ::std::string target = argv[1];
+
+  ::std::string device = "/dev/ttyUSB0";
+  serial_baud_t baud_rate = SERIAL_BAUD_57600;
+
+  ::std::string filename =
+      ::std::string(dirname(strdup(argv[0]))) +
+      "/../../../bbb_cape/src/cape/.obj/" + target + ".hex";
+
+  int file = open(filename.c_str(), O_RDONLY);
+  if (file == -1) {
+    LOG(FATAL, "open(%s, O_RDONLY) failed with %d: %s\n",
+        filename.c_str(), errno, strerror(errno));
+  }
+
+  uint16_t start_address = 0;
+  {
+    uint8_t buffer[1 /* : */ + 2 /* record size */ + 4 /* address */ +
+        2 /* record type */];
+    ssize_t bytes = read(file, buffer, sizeof(buffer));
+    if (close(file) == -1) {
+      LOG(FATAL, "close(%d) failed with %d: %s\n",
+          file, errno, strerror(errno));
+    }
+    if (bytes != sizeof(buffer)) {
+      LOG(FATAL, "read %zd bytes from %s instead of %zu\n",
+          bytes, filename.c_str(), sizeof(buffer));
+    }
+    if (buffer[0] != ':' || buffer[7] != '0' || buffer[8] != '0') {
+      LOG(FATAL, "%s isn't a valid hex file that we know how to handle\n",
+          filename.c_str());
+    }
+    for (int i = 0; i < 4; ++i) {
+      uint8_t digit = buffer[3 + i];
+      int value;
+      if (digit >= '0' && digit <= '9') {
+        value = digit - '0';
+      } else if (digit >= 'a' && digit <= 'f') {
+        value = digit - 'a';
+      } else if (digit >= 'A' && digit <= 'F') {
+        value = digit - 'A';
+      } else {
+        LOG(FATAL, "unknown hex digit %c\n", digit);
+      }
+      start_address |= value << (12 - (4 * i));
+    }
+    printf("%x\n", start_address);
+  }
+
+  parser_t *parser = &PARSER_HEX;
+  void *p_st = parser->init();
+  if (p_st == NULL) {
+    LOG(FATAL, "%s parser failed to initialize.\n", parser->name);
+  }
+  if (parser->open(p_st, filename.c_str(), 0) != PARSER_ERR_OK) {
+    LOG(FATAL, "opening file %s failed\n", filename.c_str());
+  }
+
+  serial_t *serial = serial_open(device.c_str());
+  if (serial == NULL) {
+    LOG(FATAL, "failed to open serial port %s because of %d: %s\n",
+        device.c_str(), errno, strerror(errno));
+  }
+  if (serial_setup(serial, baud_rate,
+                   SERIAL_BITS_8,
+                   SERIAL_PARITY_EVEN,
+                   SERIAL_STOPBIT_1) != SERIAL_ERR_OK) {
+    LOG(FATAL, "setting up serial port %s failed because of %d: %s\n",
+        device.c_str(), errno, strerror(errno));
+  }
+  LOG(INFO, "serial configuration: %s\n", serial_get_setup_str(serial));
+
+  if (init_bl_entry(serial, NULL /* GPIO sequence */) == 0) {
+    LOG(FATAL, "init_bl_entry(%p, NULL) failed\n", serial);
+  }
+  stm32_t *stm = stm32_init(serial, true);
+  if (stm == NULL) {
+    LOG(FATAL, "stm32_init(%p, true) failed\n", serial);
+  }
+
+  unsigned int last_byte = parser->size(p_st);
+  unsigned int size = last_byte - start_address;
+  printf("%x\n", size);
+
+  // An array of the sizes of each sector.
+  static const uint32_t kSectorSizes[12] = {0x4000, 0x4000, 0x4000, 0x4000,
+                                            0x10000, 0x20000, 0x20000, 0x20000,
+                                            0x20000, 0x20000, 0x20000, 0x20000};
+  static const int kNumSectors = sizeof(kSectorSizes) / sizeof(kSectorSizes[0]);
+  // The sector number that we're going to start writing at.
+  int start_sector = 0;
+  for (uint32_t address = 0; start_sector <= kNumSectors;
+       address += kSectorSizes[start_sector++]) {
+    if (start_sector == kNumSectors) {
+      LOG(FATAL, "start address %x is too big\n", start_address);
+    }
+    if (address > start_address) {
+      LOG(FATAL, "start address %x is not on a sector boundary\n",
+          start_address);
+    }
+    if (address == start_address) break;
+  }
+  printf("starting with sector %d\n", start_sector);
+
+  // The first sector that we're not going to erase.
+  int end_sector = 0;
+  for (uint32_t address = 0; end_sector <= kNumSectors;
+       address += kSectorSizes[end_sector++]) {
+    if (address > start_address + size) break;
+    if (end_sector == kNumSectors) {
+      LOG(FATAL, "%x bytes beyond start address of %x is too big\n",
+          size, start_address);
+    }
+  }
+  printf("not erasing sector %d\n", end_sector);
+
+  if (!stm32_erase_memory(stm, start_sector,
+                          end_sector - start_sector - 1 /* you send the
+                                                           bootloader N-1 */)) {
+    LOG(FATAL, "failed to erase memory\n");
+  }
+
+  uint32_t kFlashStart = 0x08000000;
+
+  uint8_t buffer[256];  // 256 is the biggest size supported
+  uint32_t completed = 0;
+  while (completed < size) {
+    uint32_t address = start_address + completed;
+    uint32_t length = ::std::min(size - completed, sizeof(buffer));
+    if (parser->read(p_st, buffer, &length) != PARSER_ERR_OK) {
+      LOG(FATAL, "reading file failed\n");
+    }
+    if (length == 0) {
+      LOG(FATAL, "failed to read input file\n");
+    }
+    if (!stm32_write_memory(stm, kFlashStart + address, buffer, length)) {
+      LOG(FATAL, "failed to write memory at address 0x%x\n", address);
+    }
+    uint8_t compare_buffer[sizeof(buffer)];
+    if (!stm32_read_memory(stm, kFlashStart + address, compare_buffer,
+                           length)) {
+      LOG(FATAL, "failed to read memory at address 0x%x\n", address);
+    }
+    if (memcmp(buffer, compare_buffer, length) != 0) {
+      LOG(FATAL, "verify from 0x%x to 0x%x failed\n",
+          address, address + length);
+    }
+    completed += length;
+    printf("\rWrote and verified 0x%08x/0x%08x",
+           completed, size);
+    fflush(stdout);
+  }
+  printf("\n");
+
+  if (init_bl_exit(stm, serial, NULL /* GPIO sequence */)) {
+    printf("done!\n");
+  } else {
+    LOG(FATAL, "init_bl_exit failed\n");
+  }
+}