2

I am trying to install opencv 3.4.12 in rpi4.

AFAIK, Enabling Neon flag can accelerate the performance. But in cmake output I observe that Neon feature is not detected as CPU/HW feature. (cmake ouput below)

--   CPU/HW features:
--     Baseline:
--       requested:                 NEON
--       disabled:                  VFPV3 NEON

Whereas when i run check CPU info i can see the neon flags.

pi@raspberrypi:~ $ cat /proc/cpuinfo
processor   : 0
model name  : ARMv7 Processor rev 3 (v7l)
BogoMIPS    : 108.00
Features    : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32 
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part    : 0xd08
CPU revision    : 3

processor   : 1
model name  : ARMv7 Processor rev 3 (v7l)
BogoMIPS    : 108.00
Features    : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32 
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part    : 0xd08
CPU revision    : 3

processor   : 2
model name  : ARMv7 Processor rev 3 (v7l)
BogoMIPS    : 108.00
Features    : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32 
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part    : 0xd08
CPU revision    : 3

processor   : 3
model name  : ARMv7 Processor rev 3 (v7l)
BogoMIPS    : 108.00
Features    : half thumb fastmult vfp edsp neon vfpv3 tls vfpv4 idiva idivt vfpd32 lpae evtstrm crc32 
CPU implementer : 0x41
CPU architecture: 7
CPU variant : 0x0
CPU part    : 0xd08
CPU revision    : 3

Hardware    : BCM2711
Revision    : b03114
Serial      : 100000005ce5f0a0
Model       : Raspberry Pi 4 Model B Rev 1.4

Can anyone point me what am i doing wrong here ?

5
  • You are misinterpreting the junk data you get from /proc/cpuinfo. It was broken by the Linux kernel developers.
    – Dougie
    Feb 13 at 9:28
  • 1
    So do you mean rpi4 doesnt have neon supported ? Or is there any update in kernal that can fix this ?
    – Mayank
    Feb 13 at 11:28
  • No. I mean that cpuinfo incorrectly reports what the CPU can do. Should get fixed with the switch to aarch64.
    – Dougie
    Feb 13 at 16:53
  • @Dougie I'm pretty certain the Pi 4 supports VFPV3 and NEON. If you claim the opposite, do you have any links for a reference? Feb 15 at 11:57
  • @DmitryGrigoryev I'm saying that the kernel reports it incorrectly for ARM8. But gets it right with AARCH64. Because the ARM support in the kernel is broken.
    – Dougie
    Feb 16 at 23:00
1

This appears to be a bug which is fixed in version 3.4.13. A possible workaround is to pass -DENABLE_NEON to cmake.

1
  • Thanks for pointer. I haven't checked the same...i will accept it as answer ASA i can get this working on my board. Thanks again.
    – Mayank
    Feb 15 at 15:11

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