diff --git a/bbb_cape/src/bbb/uart_reader.cc b/bbb_cape/src/bbb/uart_reader.cc
index ef90635..0a3f3c6 100644
--- a/bbb_cape/src/bbb/uart_reader.cc
+++ b/bbb_cape/src/bbb/uart_reader.cc
@@ -26,7 +26,8 @@
 namespace {
 // TODO(brians): Determine this in some way that allows easy switching for
 // testing with /dev/ttyUSB0 for example.
-const char *device = "/dev/ttyO1";
+// TODO(brians): Change back to /dev/ttyO1.
+const char *device = "/dev/ttyUSB0";
 }  // namespace
 
 UartReader::UartReader(int32_t baud_rate)
@@ -41,62 +42,77 @@
                " Did you read my note in bbb/uart_reader.cc?\n",
         device, errno, strerror(errno));
   }
+
+  {
+    termios options;
+    if (tcgetattr(fd_, &options) != 0) {
+      LOG(FATAL, "tcgetattr(%d, %p) failed with %d: %s\n",
+          fd_, &options, errno, strerror(errno));
+    }
+    if (cfsetispeed(&options, B38400) != 0) {
+      LOG(FATAL, "cfsetispeed(%p, B38400) failed with %d: %s\n",
+          &options, errno, strerror(errno));
+    }
+    if (cfsetospeed(&options, B38400) != 0) {
+      LOG(FATAL, "cfsetospeed(%p, B38400) failed with %d: %s\n",
+          &options, errno, strerror(errno));
+    }
+    cfmakeraw(&options);
+    options.c_cflag |= CLOCAL;  // ignore modem flow control
+    options.c_cflag |= CREAD;  // enable receiver
+    options.c_cflag &= ~CRTSCTS;  // disable flow control
+    //options.c_cflag |= PARENB;  // enable parity; defaults to even
+    options.c_cflag = (options.c_cflag & ~CSIZE) | CS8;  // 8 bits
+    options.c_cflag &= ~CSTOPB;  // 1 stop bit
+    options.c_iflag = 0;
+    // Replace any received characters with parity or framing errors with 0s.
+    options.c_iflag = (options.c_iflag & ~(IGNPAR | PARMRK)) | INPCK;
+    //options.c_iflag |= IGNCR | PARMRK;
+    options.c_oflag = 0;
+    options.c_lflag = 0;
+    options.c_cc[VMIN] = 0;
+    options.c_cc[VTIME] = 1;
+    if (tcsetattr(fd_, TCSANOW, &options) != 0) {
+      LOG(FATAL, "tcsetattr(%d, TCSANOW, %p) failed with %d: %s\n",
+          fd_, &options, errno, strerror(errno));
+    }
+  }
  
-  serial_struct serinfo;
-  // Must implement an ugly custom divisor.
-  serinfo.reserved_char[0] = 0;
-  if (ioctl(fd_, TIOCGSERIAL, &serinfo) < 0) {
-    LOG(FATAL, "ioctl(%d, TIOCGSERIAL, %p) failed with %d: %s\n",
-        fd_, &serinfo, errno, strerror(errno));
-  }
-  serinfo.flags &= ~ASYNC_SPD_MASK;
-  serinfo.flags |= ASYNC_SPD_CUST;
-  serinfo.custom_divisor = (serinfo.baud_base + (baud_rate_ / 2)) / baud_rate_;
-  if (serinfo.custom_divisor < 1) serinfo.custom_divisor = 1;
-  if (ioctl(fd_, TIOCSSERIAL, &serinfo) < 0) {
-    LOG(FATAL, "ioctl(%d, TIOCSSERIAL, %p) failed with %d: %s\n",
-        fd_, &serinfo, errno, strerror(errno));
-  }
-  if (ioctl(fd_, TIOCGSERIAL, &serinfo) < 0) {
-    LOG(FATAL, "ioctl(%d, TIOCGSERIAL, %p) failed with %d: %s\n",
-        fd_, &serinfo, errno, strerror(errno));
-  }
-  if (serinfo.custom_divisor * baud_rate_ != serinfo.baud_base) {
-    LOG(WARNING, "actual baudrate is %d / %d = %f\n",
-        serinfo.baud_base, serinfo.custom_divisor,
-        static_cast<double>(serinfo.baud_base) / serinfo.custom_divisor);
+  {
+    serial_struct serinfo;
+    if (ioctl(fd_, TIOCGSERIAL, &serinfo) != 0) {
+      LOG(FATAL, "ioctl(%d, TIOCGSERIAL, %p) failed with %d: %s\n",
+          fd_, &serinfo, errno, strerror(errno));
+    }
+    serinfo.reserved_char[0] = 0;
+    serinfo.flags &= ~ASYNC_SPD_MASK;
+    serinfo.flags |= ASYNC_SPD_CUST;
+    //serinfo.flags |= ASYNC_LOW_LATENCY;
+    serinfo.custom_divisor = static_cast<int>(
+        static_cast<double>(serinfo.baud_base) / baud_rate_ + 0.5);
+    if (serinfo.custom_divisor < 1) serinfo.custom_divisor = 1;
+    if (ioctl(fd_, TIOCSSERIAL, &serinfo) < 0) {
+      LOG(FATAL, "ioctl(%d, TIOCSSERIAL, %p) failed with %d: %s\n",
+          fd_, &serinfo, errno, strerror(errno));
+    }
+    if (ioctl(fd_, TIOCGSERIAL, &serinfo) < 0) {
+      LOG(FATAL, "ioctl(%d, TIOCGSERIAL, %p) failed with %d: %s\n",
+          fd_, &serinfo, errno, strerror(errno));
+    }
+    if ((serinfo.flags & ASYNC_SPD_CUST) == 0) {
+      LOG(FATAL, "can not set custom baud rate\n");
+    }
+    if (serinfo.custom_divisor * baud_rate_ != serinfo.baud_base) {
+      LOG(WARNING, "actual baudrate is %d / %d = %f\n",
+          serinfo.baud_base, serinfo.custom_divisor,
+          static_cast<double>(serinfo.baud_base) / serinfo.custom_divisor);
+    }
   }
 
   if (fcntl(fd_, F_SETFL, 0) != 0) {
     LOG(FATAL, "fcntl(%d, F_SETFL, 0) failed with %d: %s\n",
         fd_, errno, strerror(errno));
   }
-
-  termios options;
-  if (tcgetattr(fd_, &options) != 0) {
-    LOG(FATAL, "tcgetattr(%d, %p) failed with %d: %s\n",
-        fd_, &options, errno, strerror(errno));
-  }
-  if (cfsetispeed(&options, B38400) != 0) {
-    LOG(FATAL, "cfsetispeed(%p, B38400) failed with %d: %s\n",
-        &options, errno, strerror(errno));
-  }
-  if (cfsetospeed(&options, B38400) != 0) {
-    LOG(FATAL, "cfsetospeed(%p, B38400) failed with %d: %s\n",
-        &options, errno, strerror(errno));
-  }
-  cfmakeraw(&options);
-  options.c_cflag |= (CLOCAL | CREAD);
-  options.c_cflag &= ~CRTSCTS;
-  options.c_iflag = 0;
-  options.c_oflag = 0;
-  options.c_lflag = 0;
-  options.c_cc[VMIN] = 0;
-  options.c_cc[VTIME] = 1;
-  if (tcsetattr(fd_, TCSANOW, &options) != 0) {
-    LOG(FATAL, "tcsetattr(%d, TCSANOW, %p) failed with %d: %s\n",
-        fd_, &options, errno, strerror(errno));
-  }
 }
 
 UartReader::~UartReader() {
@@ -114,6 +130,11 @@
     size_t already_read = ::std::max(packet_bytes, 0);
     ssize_t new_bytes =
         read(fd_, buf_ + already_read, DATA_STRUCT_SEND_SIZE - already_read);
+    LOG(DEBUG, "read %zd, wanted %d\n", new_bytes,
+        DATA_STRUCT_SEND_SIZE - already_read);
+    for (int i = 0; i < new_bytes; ++i) {
+      LOG(DEBUG, "%x\n", buf_[i]);
+    }
     if (new_bytes < 0) {
       if (errno == EINTR) continue;
       LOG(WARNING, "read(%d, %p, %zd) failed with %d: %s\n",
diff --git a/bbb_cape/src/bbb/uart_reader_main.cc b/bbb_cape/src/bbb/uart_reader_main.cc
index 3d78039..d0fd028 100644
--- a/bbb_cape/src/bbb/uart_reader_main.cc
+++ b/bbb_cape/src/bbb/uart_reader_main.cc
@@ -8,23 +8,28 @@
 
 using ::aos::time::Time;
 
-int main() {
-  aos::Init();
+#define DO_RESET 0
 
+int main() {
+  ::aos::Init();
+
+#if DO_RESET
   // time since last good packet before we reset 
   // the board.
-  Time kPacketTimeout = Time::InSeconds(1);
+  static const Time kPacketTimeout = Time::InSeconds(1);
 
-  bbb::UartReader receiver(3000000);
-  bbb::Pin reset_pin = bbb::Pin(1, 6);
+  ::bbb::Pin reset_pin = bbb::Pin(1, 6);
   reset_pin.MakeOutput();
+#endif
 
-  DataStruct packet;
+  //::bbb::UartReader receiver(3000000);
+  ::bbb::UartReader receiver(300000);
+  //::bbb::UartReader receiver(19200);
+
   Time last_packet_time = Time::Now();
   while (true) {
-    if (!last_packet_time.IsWithin(Time::Now(),
-      kPacketTimeout.ToNSec())) {
-      
+#if DO_RESET
+    if (!last_packet_time.IsWithin(Time::Now(), kPacketTimeout.ToNSec())) {
       LOG(ERROR, "No good packets for too long. Resetting cape.\n");
       reset_pin.Write(1);
       ::aos::time::SleepFor(Time::InSeconds(1));
@@ -32,16 +37,18 @@
       
       last_packet_time = Time::Now();
     }
+#endif
 
-    if (receiver.GetPacket(&packet)) {
-      LOG(INFO, "Could not get a packet.\n");
+    DataStruct packet;
+    if (!receiver.GetPacket(&packet)) {
+      LOG(WARNING, "Could not get a packet.\n");
       continue;
     }
     last_packet_time = Time::Now();
 
+    LOG(DEBUG, "got one!\n");
     //TODO (danielp): Do stuff here with the data we got.
   }
 
-  aos::Cleanup();
-  return 0;
+  ::aos::Cleanup();
 }
diff --git a/bbb_cape/src/cape/Makefile b/bbb_cape/src/cape/Makefile
index 2439b89..39aa3aa 100644
--- a/bbb_cape/src/cape/Makefile
+++ b/bbb_cape/src/cape/Makefile
@@ -49,6 +49,7 @@
 
 OBJECTS_main_test := $(OBJECTS_main_common) \
 	robot_test \
+	uart_byte \
 
 OUTPUTS := main_test bootloader
 
diff --git a/bbb_cape/src/cape/fill_packet.c b/bbb_cape/src/cape/fill_packet.c
index 870541b..eb7d565 100644
--- a/bbb_cape/src/cape/fill_packet.c
+++ b/bbb_cape/src/cape/fill_packet.c
@@ -16,6 +16,8 @@
 #include "cape/digital.h"
 #include "cape/led.h"
 
+#include "cape/uart_byte.h"
+
 #define TIMESTAMP_TIM TIM6
 #define RCC_APB1ENR_TIMESTAMP_TIMEN RCC_APB1ENR_TIM6EN
 
@@ -84,6 +86,20 @@
   led_set(LED_ERR, 0);
   //gyro_init();
 
-  uart_common_configure(3000000);
+  //uart_common_configure(3000000);
+  uart_common_configure(300000);
+  //uart_common_configure(19200);
+#if 0
+  //for (int i = 0; i < 5; ++i) uart_byte_send(255);
+  for (int i = 0; i < 10; ++i) uart_byte_send(i + 20);
+  //uart_byte_send('a');
+  //uart_byte_send('b');
+  //uart_byte_send('c');
+  //uart_byte_send('d');
+  led_set(LED_DB, 1);
+  (void)buffer1;
+  (void)buffer2;
+#else
   uart_dma_configure(DATA_STRUCT_SEND_SIZE, buffer1, buffer2);
+#endif
 }
diff --git a/bbb_cape/src/cape/uart_common.c b/bbb_cape/src/cape/uart_common.c
index 783c154..0cb7507 100644
--- a/bbb_cape/src/cape/uart_common.c
+++ b/bbb_cape/src/cape/uart_common.c
@@ -3,20 +3,30 @@
 
 #include "cape/util.h"
 
+#define RCC_APB2ENR_UARTEN RCC_APB2ENR_USART1EN
+
 #define FPCLK 60000000
 
 // The UART is on PA9 and PA10.
 void uart_common_configure(int baud) {
   gpio_setup_alt(GPIOA, 9, 7);
   gpio_setup_alt(GPIOA, 10, 7);
-  GPIOA->OSPEEDR |= GPIO_OSPEEDER_OSPEEDR9;  // we want to go FAST!
-  RCC->APB2ENR |= RCC_APB2ENR_USART1EN;
+  //GPIOA->OSPEEDR |= GPIO_OSPEEDER_OSPEEDR9;  // we want to go FAST!
+  RCC->APB2ENR |= RCC_APB2ENR_UARTEN;
 
-  // baud = 60MHz / (8 * (2 - OVER8) * (mantissa / fraction))
-  int fraction = 8;  // the biggest it can be with OVER8=0
-  int mantissa = FPCLK * (16 /* 8 * (2 - OVER8) */ / fraction) / baud;
-  UART->BRR = (mantissa << 4) | fraction;
-  UART->CR1 = USART_CR1_UE /* enable it */ |
-      USART_CR1_M /* 9th bit for the parity */ |
-      USART_CR1_PCE /* enable parity (even by default) */;
+  // baud = 60MHz / kMultiplier * (whole_part + fraction / kMultiplier))
+  static const int kMultiplier = 16 /* 8 * (2 - OVER8) */;
+  // The divisor of FPCLK that we want (*2).
+  int divisor = FPCLK * 2 / baud;
+  // The whole-number part of the divisor.
+  int mantissa = divisor / kMultiplier / 2;
+  // The fractional part of the divisor (*2).
+  int fraction = divisor % (kMultiplier * 2);
+  UART->BRR = (mantissa << 4) | ((fraction + 1) / 2);
+  UART->CR1 =
+      //USART_CR1_M /* 9th bit for the parity */ |
+      //USART_CR1_PCE /* enable parity (even by default) */ |
+      USART_CR1_TE /* enable transmitter */ |
+      USART_CR1_RE /* enable receiver */;
+  UART->CR1 |= USART_CR1_UE;  // enable it
 }
diff --git a/bbb_cape/src/cape/uart_dma.c b/bbb_cape/src/cape/uart_dma.c
index f5c1967..8493632 100644
--- a/bbb_cape/src/cape/uart_dma.c
+++ b/bbb_cape/src/cape/uart_dma.c
@@ -3,16 +3,17 @@
 
 #include "cape/util.h"
 #include "cape/uart_common.h"
+#include "cape/led.h"
 
-#define DMA DMA1
-#define DMA_STREAM_NUMBER 7
-#define DMA_Stream DMA1_Stream7
-#define DMA_SR DMA1->HISR
-#define DMA_FCR DMA1->HIFCR
+#define DMA DMA2
+#define DMA_Stream DMA2_Stream7
+#define DMA_SR DMA2->HISR
+#define DMA_FCR DMA2->HIFCR
 #define DMA_SR_SHIFT 3
-#define DMA_Stream_IRQHandler DMA1_Stream7_IRQHandler
-#define DMA_Stream_IRQn DMA1_Stream7_IRQn
-#define RCC_AHB1ENR_DMAEN RCC_AHB1ENR_DMA1EN
+#define DMA_Stream_IRQHandler DMA2_Stream7_IRQHandler
+#define DMA_Stream_IRQn DMA2_Stream7_IRQn
+#define DMA_CHANNEL_NUMBER 4
+#define RCC_AHB1ENR_DMAEN RCC_AHB1ENR_DMA2EN
 
 #define DMA_SR_BIT(bit) (1 << (bit + 6 * DMA_SR_SHIFT))
 
@@ -22,6 +23,7 @@
 static uint8_t *volatile buffer1, *volatile buffer2;
 
 void DMA_Stream_IRQHandler(void) {
+  led_set(LED_DB, 1);
   uint32_t status = DMA_SR;
   if (status & DMA_SR_BIT(5)) {  // transfer completed
     DMA_FCR = DMA_SR_BIT(5);
@@ -34,6 +36,7 @@
     // If we're fighting somebody else writing stuff, we'll do this a bunch of
     // times, but oh well.
     DMA_Stream->CR |= DMA_SxCR_EN;
+    led_set(LED_ERR, 1);
   }
 }
 
@@ -42,27 +45,33 @@
   buffer2 = buffer2_in;
   uart_dma_callback(buffer1);
 
+  UART->CR3 = USART_CR3_DMAT;
+
   RCC->AHB1ENR |= RCC_AHB1ENR_DMAEN;
+  DMA_Stream->CR = DMA_CHANNEL_NUMBER << 25 |
+      DMA_SxCR_DBM /* enable double buffer mode */ |
+      2 << 16 /* priority */ |
+      //2 << 13 /* memory data size = 32 bits */ |
+      0 << 13 /* memory data size = 8 bits */ |
+      0 << 11 /* peripherial data size = 8 bits */ |
+      DMA_SxCR_MINC /* increment memory address */ |
+      1 << 6 /* memory to peripherial */ |
+      DMA_SxCR_HTIE | DMA_SxCR_DMEIE |
+      DMA_SxCR_TCIE | DMA_SxCR_TEIE;
   DMA_Stream->PAR = (uint32_t)&UART->DR;
   DMA_Stream->M0AR = (uint32_t)buffer1;
   DMA_Stream->M1AR = (uint32_t)buffer2;
   // This is measured in chunks of PSIZE bytes, not MSIZE.
   DMA_Stream->NDTR = bytes;
   DMA_FCR = 0xF << DMA_SR_SHIFT;
-  DMA_Stream->CR = DMA_STREAM_NUMBER << 25 |
-      DMA_SxCR_DBM /* enable double buffer mode */ |
-      2 << 16 /* priority */ |
-      2 << 13 /* memory data size = 32 bits */ |
-      0 << 11 /* peripherial data size = 8 bits */ |
-      DMA_SxCR_MINC /* increment memory address */ |
-      1 << 6 /* memory to peripherial */ |
-      DMA_SxCR_TCIE | DMA_SxCR_TEIE;
   DMA_Stream->FCR =
       DMA_SxFCR_DMDIS /* disable direct mode (enable the FIFO) */ |
-      1 /* 1/2 full threshold */;
+      //1 /* 1/2 full threshold */;
+      3 /* 100% full threshold */;
   DMA_Stream->CR |= DMA_SxCR_EN;  // enable it
   NVIC_SetPriority(DMA_Stream_IRQn, 8);
   NVIC_EnableIRQ(DMA_Stream_IRQn);
 
   uart_dma_callback(buffer2);
+  led_set(LED_Z, 1);
 }
diff --git a/bbb_cape/src/flasher/stm32_flasher.cc b/bbb_cape/src/flasher/stm32_flasher.cc
index 73f778c..35d95a7 100644
--- a/bbb_cape/src/flasher/stm32_flasher.cc
+++ b/bbb_cape/src/flasher/stm32_flasher.cc
@@ -37,8 +37,14 @@
 
   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));
+    filename = target;
+    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));
+    } else {
+      LOG(INFO, "using filename %s from the command line\n", filename.c_str());
+    }
   }
 
   uint16_t start_address = 0;