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by jdb
Tue Aug 08, 2017 7:50 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: ADC Sampling 4 channels @ 100kHz
Replies: 6
Views: 403

Re: ADC Sampling 4 channels @ 100kHz

I'm assuming you're starting a conversion and then reading the result, i.e. you need 10uS-precise access to the SPI peripheral. Isolcpus is an imperfect solution to the problem. Isolcpus will prevent the kernel userspace scheduler from running userspace processes on a specific core, but kernel threa...
by jdb
Tue Jul 25, 2017 8:48 pm
Forum: General discussion
Topic: STICKY: NEW FORUM SKIN - Comments here please.
Replies: 278
Views: 11340

Re: STICKY: NEW FORUM SKIN - Comments here please.

These comments refer to the UI elements of the theme that was presented to me by default on login. For reference I am using Firefox 54.0.1. There is no indication that drop-down lists are drop-down lists (e.g. UCP / board preferences / my board style). They are rendered the same as context tabs and ...
by jdb
Wed Jul 12, 2017 3:22 pm
Forum: General discussion
Topic: harvard architecture or von neumann architecture?
Replies: 4
Views: 456

Re: harvard architecture or von neumann architecture?

Architecturally, the Pi's ARM is a Von Neumann design (i.e. there is nothing preventing you from using the processor to write data to the addresses that contain other instructions) but there are certain Harvard-like elements in implementation. In the ARM1176, A7, and A53 cores there are two data por...
by jdb
Tue Jul 11, 2017 6:26 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: RPi3b GPIO to turn on/off USB data path
Replies: 3
Views: 310

Re: RPi3b GPIO to turn on/off USB data path

A high-speed analogue switch compatible with 3v3 levels is what you want. See the CMIO board schematic for an example (component U5): https://www.raspberrypi.org/app/uploads/2014/04/RPI-CMIO-V1_2-SCHEMATIC.pdf Though the tiny package may be hard to solder. There are many alternatives available with ...
by jdb
Fri Jun 30, 2017 2:50 pm
Forum: Advanced users
Topic: Alternative analogue audio output how?
Replies: 2
Views: 248

Re: Alternative analogue audio output how?

Would this be what you're looking for?

viewtopic.php?f=29&t=136445
by jdb
Mon Jun 19, 2017 12:14 pm
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: SMI - CS signal?
Replies: 1
Views: 147

Re: SMI - CS signal?

The SMI "cs" pins are the address pins SA0-SA5. Transfers are tied to an address which is output when the bus is active, so depending on your "active" state you need to make sure your address has the connected bit set or cleared.
by jdb
Fri Jun 16, 2017 11:57 am
Forum: Troubleshooting
Topic: Pi 3B UART limited to 9 chars?
Replies: 17
Views: 923

Re: Pi 3B UART limited to 9 chars?

An issue has been opened on Github: https://github.com/raspberrypi/linux/issues/1855 . PhilE is looking at it.
by jdb
Fri Jun 16, 2017 11:49 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: SPI1 clock is delayed?
Replies: 3
Views: 265

Re: SPI1 clock is delayed?

See here: viewtopic.php?f=44&t=96069

It looks like a hardware limitation.
by jdb
Fri Jun 16, 2017 11:08 am
Forum: General discussion
Topic: Groundhog day
Replies: 14
Views: 758

Re: Groundhog day

Just an interesting coda: https://www.raspberrypi.org/forums/viewtopic.php?f=28&t=186133 It appears the card could have its own inbuilt cache, so even reading the card could give a false result! It's a bit more complicated than that. Because of the nature of sector-to-flash page mapping, a separate...
by jdb
Thu Jun 15, 2017 6:40 pm
Forum: Troubleshooting
Topic: Intermittant video boot fault.
Replies: 2
Views: 142

Re: Intermittant video boot fault.

What happens if you swap the SD card for a new one?

Some SD cards can write-protect themselves internally (without reporting that they are damaged) after a power-off corrupts their internal state.
by jdb
Tue Jun 13, 2017 11:30 am
Forum: General discussion
Topic: Is PerPort Power Supply to each USB port feasible (RPi Bs)
Replies: 4
Views: 321

Re: Is PerPort Power Supply to each USB port feasible (RPi B

Well, given that they are completely different models, yes.
by jdb
Tue Jun 13, 2017 11:27 am
Forum: Troubleshooting
Topic: GPIO PWM Audio + WiFi Interference
Replies: 5
Views: 532

Re: GPIO PWM Audio + WiFi Interference

If you're using USB wifi, the 5V line is bouncing and coupling to the output of your amplifier. If you're using the onboard wifi, the 3v3 is bouncing and coupling to the input of your amplifier via the GPIOs. You need to buffer the output before low-pass filtering it, as seen here, bottom right: htt...
by jdb
Mon Jun 12, 2017 6:32 pm
Forum: Troubleshooting
Topic: Overheating of BCM43438 WiFi chip
Replies: 4
Views: 267

Re: Overheating of BCM43438 WiFi chip

Try get it somehow to boot, then turn off onboard wifi. Always use usb dongle for wifi! This is an incorrect solution. Under no normal conditions should the wifi chip ever get hot enough to "burn" your finger. It seems to be that the chip has either suffered mechanical damage or electrical damage d...
by jdb
Mon Jun 12, 2017 6:16 pm
Forum: General discussion
Topic: Is PerPort Power Supply to each USB port feasible (RPi Bs)
Replies: 4
Views: 321

Re: Is PerPort Power Supply to each USB port feasible (RPi B

USB hub port power control works on B+, 2B and 3B. The port VBus connections are ganged together and controlled by the USB overcurrent monitor chip. The only caveat is that the hub chip reports capabilities incorrectly - the hub reports per-port power control but only port 2 is connected, and port p...
by jdb
Wed Jun 07, 2017 2:51 pm
Forum: Astro Pi
Topic: SenseHAT as Light meter?
Replies: 1
Views: 378

Re: SenseHAT as Light meter?

The matrix LEDs are all connected to digital logic. The driver IC (that drives at constant-current) is an open-drain type input and the column selects are driven via FET to 5V. Basically, no the LEDs can't be used as photodiodes.
by jdb
Fri Jun 02, 2017 9:10 pm
Forum: Troubleshooting
Topic: Network freeze with USB camera
Replies: 2
Views: 179

Re: Network freeze with USB camera

After your wifi drops and you have to unplug the webcam, what is the output of the command vcgencmd get_throttled?
by jdb
Fri Jun 02, 2017 8:53 pm
Forum: Advanced users
Topic: Analogue audio testing
Replies: 252
Views: 75109

Re: Analogue audio testing

Given that the author is myself, pester me more? :lol:

It's on my to-do list. I also have to reduce the VPU usage % by a factor of 4 or more before this mode is ready for primetime.
by jdb
Thu Jun 01, 2017 8:21 am
Forum: Advanced users
Topic: Analogue audio testing
Replies: 252
Views: 75109

Re: Analogue audio testing

Hi, this works great if you only have one sound source, so I suspect is uses ALSA and not Pulse? If so what are the chances of supporting Pulse for mixed sounds? You can see what I mean by trying these instructions + audio_pwm_mode=2: https://www.raspberrypi.org/forums/viewtopic.php?p=1169979#p1169...
by jdb
Sun May 28, 2017 2:37 pm
Forum: Advanced users
Topic: RPI3 CPU "breakdown" voltage?
Replies: 4
Views: 440

Re: RPI3 CPU "breakdown" voltage?

Thank you for your reply. Trial and error it is then :) Not to mix it with RPI in some actual setup, this one was meant for overclock only (since you mentioned software optimization or hardware change for more performance). But as it turned out, there is no need for additional voltage increase on C...
by jdb
Tue May 23, 2017 5:26 pm
Forum: Troubleshooting
Topic: USB Game Controller and Pi Zero problems.
Replies: 4
Views: 691

Re: USB Game Controller and Pi Zero problems.

It could be that the microUSB plug is wired to auto-switch between controller (normal for the computer end) mode and device mode. So with no USB plug, the Pi tries to be a USB device, and therefore won't talk to another USB device This is likely to be the case. The OTGID pin is connected to the mic...
by jdb
Tue May 23, 2017 5:17 pm
Forum: General discussion
Topic: Fake Pi3 or just very dubious quality?
Replies: 17
Views: 940

Re: Fake Pi3 or just very dubious quality?

The RJ-45 jack is wave-soldered which means it was either not inserted properly or got pushed up by the wave. Either of these causes not getting picked up points to a potential process control issue - a component not properly seated, especially one that has mechanical alignment criticality (think ho...
by jdb
Sat May 13, 2017 4:04 pm
Forum: Off topic discussion
Topic: NHS attack on WinXP; would an RP be safer?
Replies: 43
Views: 2081

Re: NHS attack on WinXP; would an RP be safer?

Moved to OT
by jdb
Sat May 13, 2017 1:19 pm
Forum: General discussion
Topic: Using RPi3 in pressure compensated (oil-filled) enclosure?
Replies: 8
Views: 571

Re: Using RPi3 in pressure compensated (oil-filled) enclosur

I have to ask - why? I'm curious as to the background behind your question. My first thought is that, whilst most component parts seem solid, I doubt they really are. They'll possibly be a silicon wafer with) wires connecting to the pins, encapsulated in a plastic or ceramic 'box'. The remaining sp...
by jdb
Fri May 12, 2017 11:52 am
Forum: General discussion
Topic: Pi Zero W and Pi3 3v3 ripple when wifi busy
Replies: 3
Views: 335

Re: Pi Zero W and Pi3 3v3 ripple when wifi busy

You also get ripple when writing to the uSD card (charge pumps take a lot of current to build up the flash erase voltage). It's the reason we use a dedicated linear regulator for the analogue audio output - the same logic follows if you need a clean supply for anything analogue-related. Edit: for a ...
by jdb
Mon May 08, 2017 1:47 pm
Forum: General discussion
Topic: Connecting USB printer stops Pi
Replies: 11
Views: 453

Re: Connecting USB printer stops Pi

What model is your printer?

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