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Orbuculum - ARM Cortex Debug Output Processing Tools

Stop press: Orbuculum now has an active Gitter channel at ... come join the discussion.

An Orbuculum is a Crystal Ball, used for seeing things that would be otherwise invisible. A nodding reference to (the) BlackMagic (debug probe), BMP.

You can find information about using this suite on the Embedded Rambling blog at

This program is in heavy development. Check back frequently for new versions with additional functionality. The current status (23rd Jan) is that the fpga code appears stable for 1, 2 and 4 bit parallel port operation, and support has been integrated into orbuclum for it. It's not fully documented though so you might be digging through source files to use it.

For the current development status you will need to use the blackorb branch. The majority of effort at the moment is being spent on the fpga parallel trace activity.

The code is in daily use now and small issues are patched as they are found. The parallel trace hardware using a iCE40HX-8K breakout board and the icestorm tools is stable and hardware is in development.

The software runs on both Linux and OSX.

The whole suite is working OK on regular workloads. There may be some rough edges to be discovered, so please report anything unusual you find.

What is it?

Orbuculum is a set of tools for decoding and presenting output flows from the Debug pins of a CORTEX-M CPU. Originally it only used the SWO pin but it now also supports hardware for parallel tracing through the TRACE pins too using the iCE40HX-8K FPGA Breakout Board. Numerous types of data can be output through these pins, from multiple channels of text messages through to Program Counter samples. Processing these data gives you a huge amount of insight into what is really going on inside your CPU. The current tools are;

  • orbuculum: The main program and multiplexer...used as a base interface to the target by other programmes in the suite. Generally you configure this for the interface you're using and then you can just leave it running and it'll grab data from the target and make it available to clients whenever it can.

  • orbcat: A simple cat utility for ITM channel data.

  • orbdump: A utility for dumping raw SWO data to a sfile for post-processing.

  • orbtop: A top utility to see what's actually going on with your target. It can also provide dot and gnuplot source data for perty graphics.

  • orbstat: An analysis/statistics utility which can produce KCacheGrind input files. KCacheGrind is a very powerful code performance analysis tool.

  • orbtrace: The fpga configuration bitstream maker to support parallel trace operation.

A few simple use cases are documented in the last section of this document, as are example outputs of using orbtop to report on the activity of BMP while emitting SWO packets. More will be added.

The data flowing from the SWO pin can be encoded either using NRZ (UART) or RZ (Manchester) formats. The pin is a dedicated one that would be used for TDO when the debug interface is in JTAG mode.

The data flowing from the TRACE pins is clocked using a separate TRACECLK pin. There can be 1-4 TRACE pins which obviously give you much higher bandwidth than the single SWO.

Orbuculum takes this output and makes it accessible to tools on the host PC. At its core it takes the data from the source, decodes it and presents it to a set of unix fifos which can then be used as the input to other programs (e.g. cat, or something more sophisticated like gnuplot, octave or whatever). Orbuculum itself doesn't care if the data originates from a RZ or NRZ port, or at what speed....that's the job of the interface.

At the present time Orbuculum supports five devices for collecting trace from the target;

  • the Black Magic Debug Probe (BMP)
  • the SEGGER JLink
  • generic USB TTL Serial Interfaces
  • FTDI High speed serial interfaces
  • The ice40-HX8K Breakout Board for parallel trace.
  • Anything capable of saving the raw SWO data to a file, eg OpenOCD

Information about using each individual interface can be found in the docs directory. gdb setup files for each device type can be found in the Support directory.

When using SWO Orbuculum can use, or bypass, the TPIU. The TPIU adds (a small amount of) overhead to the datastream, but provides better synchronisation if there is corruption on the link. To include the TPIU in decode stack, provide the -t option on the command line. If you don't provide it, and the ITM decoder sees TPIU syncs in the datastream, it will complain and barf out. This is deliberate after I spent two days trying to find an obscure bug 'cos I'd left the -t option off...

Beware that in parallel trace the TPIU is mandatory, so therefore so is the -t option.

When in NRZ mode the SWO data rate that comes out of the chip must match the rate that the debugger expects. On the BMP speeds of 2.25Mbps are normal, TTL Serial devices tend to run a little slower but 921600 baud is normally acheivable. On BMP the baudrate is set via the gdb session with the 'monitor traceswo xxxx' command. For a TTL Serial device its set by the Orbuculum command line. Segger devices can normally work faster, but no experimentation has yet been done to find their max limits, which are probably dependent on the specific JLink you are using.

When using parallel trace you are limited by the capabilities of the FPGA configuration and the speed you can get data off the chip. The current maximum speed supported for the target is around 150MHz but you will swamp the chip very quickly if you start streaming data at that speed. The offboard link is curently limited to about 22Mbps serial. This issue will be resolved when dedicated FPGA target hardware is available (it's on its way).

Configuring the Target

Generally speaking, you will need to configure the target device to output SWD or parallel data. You can either do that through program code, or through magic incantations in gdb. The gdb approach is more flexible and the program code version is grandfathered. It's in the support directory if you want it.

In the support directory you will find a script gdbtrace.init which contains a set of setup macros for the SWO functionality. Full details of how to set up these various registers are available from and you've got various options for the type of output generated, its frequency and it's content.

Using these macros means you do not need to change your program code to be able to use facilities like orbtop. Obviously, if you want textual trace output, you've got to create that in the program!

Information about the contets of this file can be found by importing it into your gdb session with source gdbtrace.init and then typing help orbuculum. Help on the parameters for each macro are available via the help system too.

In general, you will configure orbuculum via your local .gdbinit file. Several example files are also in the Support directory. Generically, it looks like this;

source config/gdbtrace.init             <---- Source the trace specific stuff
target extended-remote /dev/ttyACM1     <-
monitor swdp_scan                       <-
file ofiles/firmware.elf                <- 
attach 1                                <---- Connect to the target
set mem inaccessible-by-default off     <-
set print pretty                        <-
load                                    <---- Load the program

start                                   <---- and get to main

enableSTM32SWD                          <*--- turn on SWO output pin on CPU

# ---------- EITHER, IF USING A BLUEPILL-------------------------
monitor traceswo 2250000                <*--- wakeup tracing on the probe
prepareSWD SystemCoreClock 2250000 1 0  <*--- Setup SWO timing (Bluepill case)

# ----------ALTERNATIVELY, FOR GENUINE BMP-----------------------
monitor traceswo                        <*--- Enable BMP traceswo output
prepareSWD ConfigCoreClock 200000 0 1   <*--- Setup SWO timing (BMP case)
# ----------END OF ALTERNATIVE-----------------------------------

dwtSamplePC 1                           <-
dwtSyncTAP 3                            <-
dwtPostTAP 1                            <-
dwtPostInit 1                           <-
dwtPostReset 15                         <-
dwtCycEna 1                             <---- Configure Data Watch/Trace

ITMId 1                                 <-
ITMGTSFreq 3                            <-
ITMTSPrescale 3                         <-
ITMTXEna 1                              <-
ITMSYNCEna 1                            <-
ITMEna 1                                <---- Enable Instruction Trace Macrocell

ITMTER 0 0xFFFFFFFF                     <---- Enable Trace Ports
ITMTPR 0xFFFFFFFF                       <---- Make them accessible to user level code

Alternatively, if you're using parallel trace via the ice40 remove the lines marked <*- above and replace them with the following;

enableSTM32TRACE                         <---- Switch on parallel trace on the STM32
prepareTRACE 4                           <---- Set up the TPIU for 4 bit output (or 2 or 1) careful to set the trace width to be the same as what you've configured on the FPGA (the -o parameter on the orbuculum command line).



  • libusb-1.0
  • libbfd (binutils-devel)
  • libelf (elfutils-libelf)
  • libftdi (For FPGA support only)

The command line to build the Orbuculum tool suite is;



make WITH_FPGA=0 if you don't need the fpga trace capture support. may need to change the paths to your libusb files, depending on how well your build environment is set up.

To build the FPGA and load it into the board, install the incredible icestorm tools from Clifford Wolf, then go into the orbtrace/src directory and type ./create. It will take about 30 seconds to compile the image and burn it to the board.


The command line options for Orbuculum are available by running orbuculum with the -h option.

A typical command line would be;

orbuculum -b swo/ -c 0,text,"%c" -v

The directory 'swo/' is expected to already exist, into which will be placed a file 'text' which delivers the output from swo channel 0 in character format. Because no source options were provided on the command line, input will be taken from a Blackmagic probe USB SWO feed.

Multiple -c options can be provided to set up fifos for individual channels from the debug device. The format of the -c option is;


ChannelNum is 0..31 and corresponds to the ITM channel. The name is the one that will appear in the directory and the FormatString can present the data using any printf-compatable formatting you prefer, so, the following are all legal channel specifiers;

-c 7,temperature,"%d \260C\n"
-c 2,hexAddress,"%08x,"
-c 0,volume,"\l%d\b\n"

Be aware that if you start making the formatting or screen handling too complex its quite possible your machine might not keep up...and then you will loose data!

Information about command line options can be found with the -h option. Orbuculum is specifically designed to be 'hardy' to probe and target disconnects and restarts (y'know, like you get in the real world). The intention being to give you streams whenever it can get them. It does not require gdb to be running, but you may need a gdb session to start the output. BMP needs traceswo to be turned on at the command line before it capture data from the port, for example.

A further fifo hwevent will be found in the output directory, which reports on events from the hardware, one event per line as follows;

  • 0,[Status],[TS] : Time status and timestamp.
  • 1,[PCAddr] : Report Program Counter Sample.
  • 2,[DWTEvent] : Report on DWT event from the set [CPI,Exc,Sleep,LSU,Fold and Cyc].
  • 3,[EventType],[ExceptionNumber] : Hardware exception. Event type is one of [Enter, Exit, Resume].
  • 4,[Comp],[RW],[Data] : Report Read/Write event.
  • 5,[Comp],[Addr] : Report data access watchpoint event.
  • 6,[Comp],[Ofs] : Report data offset event.

In addition to the direct fifos, Orbuculum exposes TCP port 3443 to which network clients can connect. This port delivers raw TPIU frames to any client that is connected (such as orbcat, and shortly by orbtop). The practical limit to the number of clients that can connect is set by the speed of the host machine.

Command Line Options

Specific command line options of note are;

-a [serialSpeed]: Use serial port and set device speed.

-b [basedir]: for channels. Note that this is actually just leading text on the channel name, so if you put xyz/chan then all ITM software channels will end up in a directory xyz, prepended with chan. If xyz doesn't exist, then the channel creation will fail silently.

-c [Number],[Name],[Format]: of channel to populate (repeat per channel) using printf formatting.

-f [filename]: Take input from specified file. (CTRL-C to abort from this)

-h: Brief help.

-i [channel]: Set Channel for ITM in TPIU decode (defaults to 1). Note that the TPIU must be in use for this to make sense. If you call the GenericsConfigureTracing routine above with the ITM Channel set to 0 then the TPIU will be bypassed.

-n: Enforce sync requirement for ITM (i.e. ITM needs to issue syncs)

-o [width]: Use the custom (ice40 FPGA) based interface (if compiled with support) at specified port width. Current fpga supports 1, 2 and 4 bit parallel operation.

-p [serialPort]: to use. If not specified then the program defaults to Blackmagic probe.

-s [address]:[port]: Set address for SEGGER JLink connection, (default none:2332)

-t: Use TPIU decoder. This will not sync if TPIU is not configured, so you won't see packets in that case.

-v: Verbose mode 0==Errors only, 1=Warnings (Default) 2=Info, 3=Full Debug.

Using orbuculum with Other info Sources

As Karl Palsson pointed out in Issue #4 on github, all of the support tools just need a stream of 'clean' trace data. Normally that is provided by the network connection that orbuculum exports, but you can also use something like netcat to generate the stream for orbuculum or its clients. For example, from a file that is written to via something like openocd;

> tail -f swo.dump.log | nc -v -v -l 9999 -k

and then;

> ./ofiles/orbuculum -g 9999 -b md/ -c 0,text,"%c"

However, that's probably over-complicated now...the orbuculum -f option supports ongoing streaming from a file directly. This information is just left here to show the flexibilities you have got available.


orbcat is a simple utility that connects to orbuculum over the network and outputs data from various ITM HW and SW channels that it finds. This output is sent to stdout so the program is very useful for providing direct input for other utilities. There can be any number of instances of orbcat running at the same time, and they will all decode data independently. They all get a seperate networked data feed. A typical use case for orbcat would be to act as a stdin for another example of doing this to just replicate the data delivered over ITM Channel 0 would be

orbcat -c 0,"%c"

...note that any number of -c options can be entered on the command line, which will combine data from those individual channels into one stream. Command line options for orbcat are;

-c [Number],[Format]: of channel to populate (repeat per channel) using printf formatting. Note that the Name component is missing in this format because orbcat does not create fifos.

-h: Brief help.

-i [channel]: Set Channel for ITM in TPIU decode (defaults to 1). Note that the TPIU must be in use for this to make sense. If you call the GenericsConfigureTracing routine above with the ITM Channel set to 0 then the TPIU will be bypassed.

-n: Enforce sync requirement for ITM (i.e. ITM needsd to issue syncs)

-s [server]:[port]: to connect to. Defaults to localhost:3443 to connect to the orbuculum daemon. Use localhost:2332 to connect to an existing Segger J-Link..

-t: Use TPIU decoder. This will not sync if TPIU is not configured, so you won't see packets in that case.

-v: Verbose mode.


orbtop is a simple utility that connects to orbuculum over the network and samples the Program Counter to identify where the program is spending its time. By default it will update its statistical output once per second. For code that matches to a function the the source file it will totalise all of the samples to tell you how much time is being spent in that function. Any samples that do not match to an identifiable function are reported as 'Unknown'.

As with Orbcat there can be any number of instances of orbtop running at the same time, which might be useful to perform sampling over different time horizons. A typical invocation line for orbtop would be;

orbtop -e ~/Develop/STM32F103-skel/ofiles/firmware.elf

...the pointer to the elf file is always needed for orbtop to be able to recover symbols from.

One useful command line option for orbtop (and indeed, for the majority of the rest of the suite) is -s localhost:2332, which will connect directly to a SEGGER J-Link you might have exporting its port, with no requirement for the orbuculum multiplexer in the way.

Command line options for orbtop are;

-c [num]: Cut screen output after number of lines.

-d [DeleteMaterial]: to take off front of filenames (for pretty printing).

-e: Set elf file for recovery of program symbols. This will be monitored and reloaded if it changes.

-h: Brief help.

-i [channel]: Set Channel for ITM in TPIU decode (defaults to 1). Note that the TPIU must be in use for this to make sense. If you call the GenericsConfigureTracing routine above with the ITM Channel set to 0 then the TPIU will be bypassed.

-l: Aggregate per line rather than per function

-m [MaxHistory]: Number of intervals to record in history file

-n: Enforce sync requirement for ITM (i.e. ITM needs to issue syncs)

-o [filename]: Set file to be used for output history

-r <routines>: Number of lines to record in history file

-s [server]:[port]: to connect to. Defaults to localhost:3443

-t: Use TPIU decoder. This will not sync if TPIU is not configured, so you won't see packets in that case.

-v: Verbose mode.

Using the ice40HX8K board

There are a set of LEDs on the HX8K board which show the status of the communication links as follows;

  • D9: Sync has been established with the target.
  • D8: Data Receive from host computer.
  • D7: Data Send to host computer.
  • D6: Heartbeat
  • D2: Data overflow (too much data for FPGA to host link).

For normal operation you can burn the program image into the configuration serial memory (J7:1-2, J6:2-4, and J6:1-3). For development just load it directly (J6:1-2 and J6:3-4. Jumper J7 not installed). See Pg. 5 of the iCE40HX-8K Breakout Board User's Guide for more information.

The ice40 breakout board is connected to the target via J2 as follows;

  • traceDin[0] C16
  • traceDin[1] D16
  • traceDin[2] E16
  • traceDin[3] F16
  • traceClk H16

Obviously you don't need the whole of traceDin[0..3] if you're only using 1 or 2 bit trace.


A whole chunk of work has gone into making sure the dataflow over both the SWO link and parallel Trace is reliable....but it's pretty dependent on the debug interface itself. The TL;DR is that if the interface is reliable then Orbuculum will be. There are factors outside of our control (i.e. the USB bus you are connected to) that could potentially break the reliabilty but there's not too much we can do about that since the SWO link is unidirectional (no opportunity for re-transmits). The following section provides evidence for the claim that the link is good;

A test 'mule' sends data flat out to the link at the maximum data rate of 2.25Mbps using a loop like the one below;

while (1)
    for (uint32_t r=0; r<26; r++)
        for (uint32_t g=0; g<31; g++)

100MB of data (more than 200MB of actual SWO packets, due to the encoding) was sent from the mule via a BMP where the output from swolisten chan00 was cat'ted into a file;

cat swo/chan00 > o

....this process was interrupted once the file had grown to 100MB. The first and last lines were removed from it (these represent previously buffered data and an incomplete packet at the point where the capture was interrupted) and the resulting file analysed for consistency;

sort o | uniq -c

The output was;


(On inspection, the last line of recorded data was indeed a 'D' line).

Using SWO in Battle

SWO gives you a number of powerful new capabilities in your debug arsenal. Here are a few examples....if you have more to add please send me an email.

Multi-channel Debug

The easiest and most obvious use of SWO is to give you multi-channel debug capability. By adding multiple '-c' definitions to the orbuculum comand line you can create multiple fifos which will each emit data of interest. So, for the simple case of two distinct serial streams, something like the following will suffice;

-c 0,out0,"%c" -c 1,out1,"%c"

...this will create two fifos in your output directory, out0 and out1, each with distinct output data. By default the CMSIS provided ITM_SendChar routine only outputs to channel0, so you will need a new routine that can output to a specified channel. Something like;

static __INLINE uint32_t ITM_SendChar (uint32_t c, uint32_t ch)
  if ((CoreDebug->DEMCR & CoreDebug_DEMCR_TRCENA_Msk)  &&      /* Trace enabled */
      (ITM->TCR & ITM_TCR_ITMENA_Msk)                  &&      /* ITM enabled */
      (ITM->TER & (1ul << c)        )                    )     /* ITM Port c enabled */
    while (ITM->PORT[c].u32 == 0);
    ITM->PORT[c].u8 = (uint8_t) ch;
  return (ch);

Now, this works perfectly for chars, but you can also write longer values into the transit buffer so if, for example, you wanted to write 32 bit values from a calculation, just update the routine to take int32_t and change the channel definition to be something more like -c 4,calcResult,"%d".

Mixing Channels

It gets more complicated when you want to mix output from individual channels together. In this circumstance you can either write a bit of script to merge the channels together, or you can use orbcat to do the same thing from the command line. So if, for example, you wanted to merge the text from channel0 with the 32 bit values from channel 4, an orbcat line such as this would do the job;

orbcat -c 0,"%c" -c 4,"\nResult=%d\n"

...its obvious that the formatting of this buffer is completely dependent on the order in which data arrive from the target, so you might want to put some 'tags' or differentiators into each channel to keep them distinct - a typical mechanism might be to use commas to seperate the flows into different columns in a CSV file.

Multiple Simulteneous Outputs

Orbuculum will place fifos for any defined channels (plus the hardware event channel) in the specified output directory. It will simulteneously create a TCP server to which an arbitary number of clients can connect. Those clients each decode the data flow independently of orbuculum, so you can present the data from the target simulteneously in multiple formats (you might log it to a file while also processing it via a plot routine, for example). You can also use the source code for orbcat or orbtop as the basis for creating your own specific decoders (and I'd really appreciate a copy to fold into this suite too please!).

Using Orbtop

Orbtop is an example client to orbuculum which processes the PC sampling information to identify what routines are running at any point in time. This is essential information to understand what your target is actually doing and once you've got this data you'll find you become addicted to it! Just running orbtop with the details of your target binary is enough for orbtop to do its magic (along with information about the configuration of the incoming SWO stream, of course);

orbtop -t -i 9 -a -e firmware.elf

orbtop can aggregate per function or per program line. By default it aggregates per function but to work per-line just add the -l option...usually that gives you too much information though.

The amount (and indeed, presence) of sample data is set by a number of configuration options. These can be set from program code, but it's more flexible to set them from gdb. The main ones are;

  • dwtSamplePC : Enable or disable Program Counter sample generation
  • dwtPostTap : Set the count rate for the PC interval counter at either bit 6 or bit 10 of the main CPU clock.
  • dwtPostInit : set the initial value for the PC interval counter (this defines when the first sample is've got to be pretty precise if this is important to you!).
  • dwtPostReset : Set the reload value for the PC Interval Counter (higher values = slower counting).
  • dwtCycEna : Enable the cycle counter input (i.e. switch the whole thing on). You won't get far without this set!

The maximum speed at which you can generate samples is defined by the speed of your SWO connection but, with a 72MHz CPU, the slowest settings (dwtPostTap 1 and dwtPostReset 15) still generate about 4000 samples per second, so you will get useful information at that level of resolution. There is a risk that you could miss frequent, but short, routines if you're running too slow, so do vary the speeds to make sure you get consistent results...on the other hand running too fast will lead to flooding the SWO and potentially missing other important data such as channel output. You do not need to restart orbuculum or orbtop in order to change the parameters in gdb - just CTRL-C, change, and restart. With a setting of dwtPostReset 1 there are no overflows when using a async interface at 2.25Mbps, which equates to 35200 Program Counter samples per second.

Here's a typical example of orbtop output for a Skeleton application based on FreeRTOS with USB over Serial (CDC) support. This table is updated once per second;

 97.90%     4308 ** Sleeping ** 
  1.25%       55 USB_LP_CAN1_RX0_IRQHandler
  0.20%        9 xTaskIncrementTick
  0.13%        6 Suspend
  0.09%        4 SysTick_Handler
  0.06%        3 Resume
  0.06%        3 __WFI
  0.04%        2 vTaskSwitchContext
  0.04%        2 TIM_Cmd
  0.02%        1 prvAddCurrentTaskToDelayedList
  0.02%        1 xTaskResumeAll
  0.02%        1 vTaskDelay
  0.02%        1 PendSV_Handler
  0.02%        1 __ISB
  0.02%        1 taskIn
  0.02%        1 statsGetRTVal
  0.02%        1 taskOut
            4400 Samples

orbtop can also generate graph output. You will find utilities to support this for gnuplot in the Support directory. Just start orbtop with the option -o <filename> to generate the output data and then run Support/orbtop_plot to generate the output. By default it generates pdf graphs once per second, but that's easily changed.


Orbuculum was pointed at a a BMP instance (running on a 72MHz STM32F103C8) both with and without SWO running in asynchronous mode at 2.25Mbps.

Firstly, without SWO;

 26.96%     1186 gdb_if_update_buf
 23.23%     1022 stm32f103_ep_read_packet
 21.82%      960 gdb_if_getchar_to
  6.66%      293 cdcacm_get_config
  6.54%      288 platform_timeout_is_expired
  5.61%      247 usbd_ep_read_packet
  4.86%      214 platform_time_ms
  3.90%      172 cdcacm_get_dtr
  0.13%        6 _gpio_clear
  0.06%        3 gpio_set_mode
  0.04%        2 swdptap_turnaround
  0.04%        2 swdptap_seq_out
  0.02%        1 swdptap_bit_in
  0.02%        1 swdptap_bit_in
  0.02%        1 swdptap_turnaround
  0.02%        1 platform_timeout_set
            4399 Samples

...and then, with SWO running (note that in this second case the sample frequency had to be increased to be able to see the impact, which is reflected in dma1_channel5_isr and to a much lesser degree in trace_buf_drain). When this trace was taken the target was emitting nearly 18000 PC samples per second, encoded in TPIU frames.

 18.17%     3198 stm32f103_ep_read_packet
 17.35%     3054 gdb_if_getchar_to
 15.05%     2648 gdb_if_update_buf
 11.02%     1940 usbd_ep_read_packet
  9.24%     1627 platform_time_ms
  9.07%     1597 platform_timeout_is_expired
  7.93%     1396 cdcacm_get_dtr
  4.78%      842 cdcacm_get_config
  4.72%      831 dma1_channel5_isr
  1.52%      268 usb_copy_to_pm
  0.45%       80 stm32f103_poll
  0.17%       31 trace_buf_drain
  0.06%       12 usb_lp_can_rx0_isr
  0.05%        9 gpio_set_mode
  0.03%        7 swdptap_turnaround
  0.03%        7 swdptap_turnaround
  0.03%        7 _gpio_clear
  0.03%        7 usbd_poll
  0.03%        6 swdptap_seq_out_parity
  0.02%        5 swdptap_seq_out
  0.02%        4 swdptap_seq_in_parity
  0.01%        3 adiv5_swdp_low_access
  0.01%        2 swdptap_bit_in
  0.01%        2 swdptap_bit_out
  0.01%        2 _gpio_set
  (Anthing < 0.01% removed)
           17594 Samples