poc:2025:raspberry-pi-vep

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poc:2025:raspberry-pi-vep [2025/07/28 14:06] – fabriciopoc:2025:raspberry-pi-vep [2025/08/20 18:41] (current) – fabricio
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 ===== Quick Summary ===== ===== Quick Summary =====
  
-  * **Status**: ⏸️ On Hold +  * **Status**: 🟡 In Progress 
-  * **Duration**: ~February 2025  +  * **Duration**: Attempt 1) February-April 2025 (failed); Attempt 2) August 2025 (success!) 
   * **Type**: Hardware/Possible Product     * **Type**: Hardware/Possible Product  
   * **Repository**: [[https://code.rekonas.com/fabricio/vep_rpi|Code Repo]] |  [[https://code.rekonas.com/fabricio/vep_ADR/|ADRs]]     * **Repository**: [[https://code.rekonas.com/fabricio/vep_rpi|Code Repo]] |  [[https://code.rekonas.com/fabricio/vep_ADR/|ADRs]]  
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   * OS: Raspbian without Desktop   * OS: Raspbian without Desktop
   * Access via SSH in WIFI, directly providing credentials when writing the Image onto the SD card   * Access via SSH in WIFI, directly providing credentials when writing the Image onto the SD card
 +  * video goggles (Bigeyes H3). 57 Degrees field of view.
  
 ** Software Used **: ** Software Used **:
-  * C + Cmake, using libDRM +  * Visual Stimuli with C + Cmake, using libDRM 
-  * Translated the Python Code from [[https://github.com/pieeg-club/EEGwithRaspberryPI|the EEGwithRaspberryPI Repo]]+  * Initial attempt on EEG Recording were with  C. Second Attempt relied on rust, with more optimized code using an interrupt listener for the GPIO events. 
 +  * The Setup is done via ansible playbooks, which are available in the repo. 
 +  * Reference Python Code used is from [[https://github.com/pieeg-club/EEGwithRaspberryPI|the EEGwithRaspberryPI Repo]]
   * Code available under: [[https://code.rekonas.com/fabricio/vep_rpi|https://code.rekonas.com/fabricio/vep_rpi]]   * Code available under: [[https://code.rekonas.com/fabricio/vep_rpi|https://code.rekonas.com/fabricio/vep_rpi]]
- 
-======= Additional Notes ======= 
- 
-A few initial key insights about the PiEEG Code: 
-  * The code uses the BOARD numbering mode for the GPIO pins. 
-  * Pin 37 is used as the "DRDY" (data ready) pin. 
-  * A lot of settings are set to the ADS1299, but in an intransparent way via encoding the bit flags via hex codes. 
- 
- 
-Quite a few things may be set via the ads1299 registers: 
- 
-  * The sampling rate is set in "config1" and defaults to 250 but can be changed.  By default config1 is set to 0x96, which translates to the binary number `10010110`. The last 3 digits denote the sampling rate. You can find the encoding in Table 13 [[https://www.ti.com/document-viewer/ADS1299/datasheet#detailed-description/SBAS4597851|here]] 
  
  
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 ===== Key Findings ===== ===== Key Findings =====
 ==== What Worked ==== ==== What Worked ====
-  * A small test with the Pi-EEG shield when looking at alpha waves seemed promising in terms of the data quality.+  * Eyes Open / Closed + Chewing worked fine. {{ :poc:2025:eyesopenclosed.png?400 |}}
   * The Checkerboard pattern using the libdrm worked well. Synchronization via the screen refreshment rate is possible.   * The Checkerboard pattern using the libdrm worked well. Synchronization via the screen refreshment rate is possible.
   * Setting a high priority to the process in combination with a preemptible Kernel setting (i.e. Desktop mode- NOT server mode) works well in terms of latency, although it is not a full substitute for the realtime kernel.    * Setting a high priority to the process in combination with a preemptible Kernel setting (i.e. Desktop mode- NOT server mode) works well in terms of latency, although it is not a full substitute for the realtime kernel. 
   * Using the Video-Display-Glasses with the rPi was no issue at all and worked well, even though the display was a bit small. No software changes were required, as it was simply treated as another display.   * Using the Video-Display-Glasses with the rPi was no issue at all and worked well, even though the display was a bit small. No software changes were required, as it was simply treated as another display.
   * The low-level graphics interface worked well, but it can get quite complicated very quickly. There is a need to write ahead into the buffer to avoid tearing.   * The low-level graphics interface worked well, but it can get quite complicated very quickly. There is a need to write ahead into the buffer to avoid tearing.
 +  * VEP Measurements {{ :poc:2025:recording_1.png?400 |}}{{ :poc:2025:recording_2.png?400 |}}
  
 ==== What Didn't Work ==== ==== What Didn't Work ====
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 The C code is outdated, and there is essentially no explanation. It was necessary to look at the python code and translate it to C. The C code is outdated, and there is essentially no explanation. It was necessary to look at the python code and translate it to C.
  
-**Measuring the actual VEPs**: 
  
-I did not manage to nicely measure the VEP. It's unclear what the cause is, as too many things were changed at once. +==== Surprises & Insights ==== 
-Possible culprits are:+  * Moving to rust did help for a more reliable implementation and easier testing and building. 
 +  * There are a LOT of different ways for low-level interaction with the display. The "displaybuffer" is ancient and should NOT be used. The newer kernel mode setting is absolutely overkill and hard to work with. Libdrm seemed like a nice middleground.  
  
-  * Parallel Processing in C without unit tests (or in general C code, as I'm inexperienced there). 
-  * The PiEEG / ads1299 interface I used in C. I reused the same GPIO pins  and signals as in the python code, but the code translation might have introduced some oversights. 
-  * Higher Sampling Rate: The initial test was done on a lower (default) sampling rate. The sampling rate was increased by a large factor, and it is unclear to me if this is a.) supported by the shield and b.) if any flags on the ADS1299 shield have to be changed. 
  
- +A few initial key insights about the PiEEG Code:
-==== Surprises & Insights ====+
   * The PiEEG code is not very helpful, and continuation of the project requires understanding of the underlying ADS1299 chip.   * The PiEEG code is not very helpful, and continuation of the project requires understanding of the underlying ADS1299 chip.
-  * Moving to rust would help for a more reliable implementation and easier testing and building. +  * The code uses the BOARD numbering mode for the GPIO pins. 
-  * There are a LOT of different ways for low-level interaction with the display. The "displaybuffer" is ancient and should NOT be used. The newer kernel mode setting is absolutely overkill and hard to work with. Libdrm seemed like a nice middleground. +  * Pin 37 is used as the "DRDY" (data ready) pin. 
 +  * A lot of settings are set to the ADS1299, but in an intransparent way via encoding the bit flags via hex codes. 
 + 
 +Quite a few things may be set via the ads1299 registers: 
 + 
 +  * The sampling rate is set in `config1` and defaults to `250` but can be changed.  By default config1 is set to `0x96`, which translates to the binary number `10010110`. The last 3 digits denote the sampling rate. You can find the encoding in Table 13 [[https://www.ti.com/document-viewer/ADS1299/datasheet#detailed-description/SBAS4597851|here]] 
  
 ===== Recommendations ===== ===== Recommendations =====
-**Should we proceed?**: Maybe+**Should we proceed?**: Yes
  
 **If yes, what needs to happen?** **If yes, what needs to happen?**
   * A reimplementation either in rust, or by someone with a better understanding of C.   * A reimplementation either in rust, or by someone with a better understanding of C.
   * More fine grained practical tests to rule out error sources.    * More fine grained practical tests to rule out error sources. 
 +====== Open Issues ====== 
 +The scale / unit that is measured is off / wrong.
  
 ====== External Ressources ====== ====== External Ressources ======
  • poc/2025/raspberry-pi-vep.1753711593.txt.gz
  • Last modified: 2025/07/28 14:06
  • by fabricio