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0198-2024-04-03.md

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3 Apr 2024

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Animation of tt04-raybox-zero glitching

Late yesterday I got the tt04-raybox-zero GL sim working and it exhibited what looks like the same error as seen in silicon. In a way, this is a good thing, because it hopefully reveals that the problem was in the final synthesised output, rather than a malfunction of the fabrication or a layout that was unstable (e.g. bad timing).

The cocotb test code is found in the 1.0-test branch. NOTE: Coming back to edit this journal now in late May, I've got outstanding changes in my working repo that were probably used to generate the results below, but at the time of writing my latest commit in the 1.0-test branch is 653f212. For more info and updates, see 0204.

Here's a rendering of the first 220 frames after reset:

rbz10-test-gl.mp4

This was created by:

  1. Modifying tb.v to disable VCD dump; otherwise it will grow to be too large after a handful of frames.
  2. Modifying test.py to write out a new .ppm file after every 525 lines.
  3. Writing a simple shell script to convert all .ppm files to .png.
  4. Renaming all the files to just 0000.png, 0001.png, etc... and then importing into Adobe Premiere Pro as an image sequence.

Fixing VT-x on my L7 laptop for VirtualBox

Indication of what we don't want, as seen in msinfo32:

Screenshot showing Virtualization-based security is running

Likewise, running this in PowerShell...

Get-CimInstance -ClassName Win32_DeviceGuard -Namespace root\Microsoft\Windows\DeviceGuard

...shows:

AvailableSecurityProperties                  : {1, 2, 3, 5...}
CodeIntegrityPolicyEnforcementStatus         : 2
InstanceIdentifier                           : 4ff40742-2649-41b8-bdd1-e80fad1cce80
RequiredSecurityProperties                   : {0}
SecurityFeaturesEnabled                      : {0}
SecurityServicesConfigured                   : {2}
SecurityServicesRunning                      : {2}
UsermodeCodeIntegrityPolicyEnforcementStatus : 0
Version                                      : 1.0
VirtualizationBasedSecurityStatus            : 2
VirtualMachineIsolation                      : False
VirtualMachineIsolationProperties            : {0}
PSComputerName                               :

Here's what I did by following this guide:

  1. Shut down my VirtualBox VMs and quit VirtualBox.
  2. Shut down all other software except for VSCode and Google Chrome (since I'm working in both of them to do this fix).
  3. Use Windows "search button" and search for cmd. Right-click and select 'Run as Administrator'.
  4. In that Admin command prompt, do: 
    bcdedit /set hypervisorlaunchtype off
bcdedit /set vsmlaunchtype Off
rem Doesn't work: DISM /Online /Disable-Feature:Microsoft-Hyper-V
  5. Run regedit, go to HKLM\SYSTEM\CurrentControlSet\Control\DeviceGuard, then:
    • Create a REG_DWORD called EnableVirtualizationBasedSecurity and set it to 0.
    • Go into Scenarios\HypervisorEnforcedCodeIntegrity and change Enabled to 0.
    • Also add a REG_DWORD called Locked set to 0.
    • Then go to HKLM\SYSTEM\CurrentControlSet\Control\Lsa and...
    • Create REG_DWORD called LsaCfgFlags = 0.
    • Then go to HKLM\SOFTWARE\Policies\Microsoft\Windows and...
    • Create REG_DWORD called DeviceGuard\LsaCfgFlags = 0.
  6. Go to Start > Settings > Privacy & Security > Windows Security > Device security > Core isolation: Core isolation details > Memory integrity: Turn it OFF
  7. shutdown -s -t 2
  8. Power back on and press F2 key repeatedly to access Lenovo BIOS.
  9. In the BIOS:
    • Disable: "Device Guard" (it was already off) and "Secure boot".
    • Make sure Intel virtualisation options are turned on.
    • Unplug the mains power, and activate the "Disable Built-in battery" option, which will power off the laptop.
  10. Wait at least 20sec, then plug in mains power, and press the power button to power on.

Now msinfo32 seems to confirm that VBS and related stuff is disabled:

msinfo32 shows VBS disabled

Likewise, this seems to confirm also:

PS C:\Users\Maurovics> Get-CimInstance -ClassName Win32_DeviceGuard -Namespace root\Microsoft\Windows\DeviceGuard


AvailableSecurityProperties                  : {1, 2, 3, 5...}
CodeIntegrityPolicyEnforcementStatus         : 2
InstanceIdentifier                           : 4ff40742-2649-41b8-bdd1-e80fad1cce80
RequiredSecurityProperties                   : {0}
SecurityFeaturesEnabled                      : {0}
SecurityServicesConfigured                   : {0}
SecurityServicesRunning                      : {0}
UsermodeCodeIntegrityPolicyEnforcementStatus : 0
Version                                      : 1.0
VirtualizationBasedSecurityStatus            : 0
VirtualMachineIsolation                      : False
VirtualMachineIsolationProperties            : {0}
PSComputerName                               :

From what I can tell, my VirtualBox VMs now run with proper virtualisation, though I was unable to start any saved-running-state VMs ('Zero to ASIC Course MPW8' was in this state, so I had to 'Discard' the state, then boot it normally, then power it off, then turn on 'Enable Nested VT-x/AMD-V').

In future, or for someone else, these links might help too:

Analog course beta

  • I'm using my anton-analog-alpha VM. I set this one up manually.
  • echo $PDK_ROOT	
# => /home/anton/.volare/volare/sky130/versions/bdc9412b3e468c102d01b7cf6337be06ec6e9c9a
echo $PDK	
# => sky130A
  • My TT06 repo is https://github.com/algofoogle/tt06-grab-bag (created from template: https://github.com/TinyTapeout/tt06-analog-template)
  • I've done a basic CMOS inverter and testbench in xschem. It also models the expected Tiny Tapeout analog output parasitics.
  • The TT parasitics make for a very weak output and long slew at 25MHz, so I increased the size of the PFET/NFET transistor widths by 4× from 2/1 to 8/4, and it made it somewhat acceptable.