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by tom.k.cook
Fri Jun 22, 2018 11:05 am
Forum: Interfacing (DSI, CSI, I2C, etc.)
Topic: SPI DMA and continuous transfers
Replies: 2
Views: 2300

SPI DMA and continuous transfers

I'm building a project using the MCP3914 8-channel analog front end (ie ADC) device connected to the Raspberry Pi's SPI peripheral. The device has a continuous read mode where you request the value of one register then hold the CS low and it cycles through all of the registers, transmitting the valu...
by tom.k.cook
Wed Mar 15, 2017 5:52 pm
Forum: Device Tree
Topic: SC16IS752 (SC16IS7XX driver) Device Tree problem
Replies: 46
Views: 23037

Re: SC16IS752 (SC16IS7XX driver) Device Tree problem

Thanks for a very helpful writeup. I've got a Pi with two SC16IS752s connected by I2C. I wonder if you could clear up two points for me: 1. According to the datasheet, the I2C addresses are in the range 0x90 to 0xAE and I thought I had selected addresses 0x98 and 0xAE, but i2cdetect shows devices at...
by tom.k.cook
Thu Mar 09, 2017 5:48 pm
Forum: Raspbian
Topic: Kernel source for Raspbian image?
Replies: 2
Views: 1281

Kernel source for Raspbian image?

I've just downloaded 2017-03-02-raspbian-jessie.img. It's running kernel 4.4.50+. Where can I get the source for this kernel as built in the distribution? The rpi-4.4.y branch of https://github.com/raspberrypi/linux doesn't include it - the HEAD of that branch is apparently still 4.4.48. Is this tag...
by tom.k.cook
Fri Jan 20, 2017 5:12 pm
Forum: Advanced users
Topic: 2.8V interfacing
Replies: 2
Views: 648

2.8V interfacing

I'm trying to use the Raspberry Pi's UART (on GPIO14 and 15) to interface to a SIM5320E GSM module. The UART on the SIM5320E is 2.8V logic - logic high is at least 2.15V. I can't find anywhere the logic level range for the GPIO pins on the Pi. Will driving them with 2.15V work? I already need some l...
by tom.k.cook
Mon Feb 02, 2015 6:13 am
Forum: General discussion
Topic: Raspberry Pi 2
Replies: 161
Views: 24107

Re: Raspberry Pi 2

Agreed, either SATA or USB3 would make these an almost serious desktop replacement. I think it would take a bit more than *that* to be a "serious desktop replacement". To do so I'd want a quad-core A-57, and at least 2 SATA ports. But the Pi2 should be pretty good for a fair amount of stuff and pre...
by tom.k.cook
Mon Feb 02, 2015 5:16 am
Forum: General discussion
Topic: Raspberry Pi 2
Replies: 161
Views: 24107

Re: Raspberry Pi 2

W. H. Heydt wrote:On the other hand, I don't see a need for GbE, but I'd sure like a native SATA connector...or later development. However, for my uses, the Pi2 has everything it needs.
Agreed, either SATA or USB3 would make these an almost serious desktop replacement.
by tom.k.cook
Mon Feb 02, 2015 4:25 am
Forum: General discussion
Topic: Raspberry Pi 2
Replies: 161
Views: 24107

Re: Raspberry Pi 2

SpazzTechTom appears to have the only link I can find of someone selling the thing - all the other Australian resellers are still touting the Model B+ (one of them at about a 33% discount, for two days only - cheeky!)
by tom.k.cook
Mon Feb 02, 2015 2:18 am
Forum: General discussion
Topic: Raspberry Pi 2
Replies: 161
Views: 24107

Raspberry Pi 2

I've read the sticky thread at the top of the forum. However, the Raspberry Pi 2 is making some press today: http://www.theregister.co.uk/2015/02/02/raspberry_pi_model_2/ In fact, according to The Register, it is released today. But raspberrypi.org makes no reference to it, that I can see. Is there ...
by tom.k.cook
Fri Dec 27, 2013 4:14 pm
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

With what settings did you run cyclictest?
by tom.k.cook
Tue Dec 24, 2013 11:52 am
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

Presumably you are still trying to build in the SDHCI/MMC drivers into the kernel, so it's still trying to mount the SD card, so it still crashes.
by tom.k.cook
Wed Dec 18, 2013 1:13 pm
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

You could try reading the rest of the thread. The problem is that the SDHCI driver doesn't work in RT. The solution is to put the root partition on a USB stick or use AutoStatic's patch above: http://www.raspberrypi.org/phpBB3/viewt ... 80#p381480
by tom.k.cook
Wed Jun 26, 2013 2:45 pm
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

They are quite different. Xenomai (so I understand) runs as a hypervisor-style kernel with RT tasks run in parallel with the linux kernel, whereas PREEMPT_RT gives you real-time latencies in the linux userspace. Each has advantages and disadvantages; Xenomai makes it easier to give low latencies, bu...
by tom.k.cook
Fri Jun 21, 2013 2:47 pm
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

A quick update: The problem with cyclictest took me a long time to figure out, but its easy when you get there: > sudo -s > mount -t debugfs none /sys/kernel/debug > echo dwc_otg_hcd_handle_fiq > /sys/kernel/debug/tracing/set_ftrace_notrace > ./cyclictest -p95 -m -f -b 1000 This no longer crashes. O...
by tom.k.cook
Fri Jun 21, 2013 2:39 pm
Forum: Troubleshooting
Topic: USB FIQ testing....
Replies: 181
Views: 72189

Re: USB FIQ testing....

Hi Gordon, One issue with the current source on github (I'm using the 3.8.y branch, but I believe it is common to all of them) is that there is no protection from data aborts in the FIQ handler. This means that attempts to use ftrace without first filtering out the dwc_otg FIQ handler cause a kernel...
by tom.k.cook
Sun May 19, 2013 2:20 pm
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

aaa801 wrote:
tom.k.cook wrote:Any luck with cyclictest -W or-f?
I didn't build the kernel with tracer support, also doesn't -f need -b?
Il recompile the kernel in a sec
Yes it does. I've got 3.6rt kernels to this point but they crash when tracers are enabled .
by tom.k.cook
Sun May 19, 2013 8:47 am
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

Any luck with cyclictest -W or-f?
by tom.k.cook
Mon May 13, 2013 9:08 am
Forum: Advanced users
Topic: How to speed up boot time if run headless?
Replies: 28
Views: 73751

Re: How to speed up boot time if run headless?

I don't have any numbers to put to it, but it's almost universally true that linux boot times are IO-bound. Faster storage will give you faster boots. This seems to be borne out by other comments here - people with a class 10 SDHC card have 10 seconds boots, people with a rotten class 2 SD card have...
by tom.k.cook
Sun May 12, 2013 4:46 pm
Forum: Advanced users
Topic: sdhci-bcm2708 as a module
Replies: 0
Views: 650

sdhci-bcm2708 as a module

Can someone responsible for the BCM2708 SD card driver please comment on the possibility of building it as a module? I've attempted the following: CONFIG_MMC_SDHCI_BCM2708=m Moved the definition of `enable_llm` from sdhci-bcm2708.c to sdhci.c Exported `enable_llm`, `sdhci_spin_lock` and `sdhci_spin_...
by tom.k.cook
Sun May 12, 2013 4:08 pm
Forum: Advanced users
Topic: Acces /dev/mem with the apache2 user
Replies: 9
Views: 6154

Re: Acces /dev/mem with the apache2 user

Can I just note that giving apache write access to raw memory is dreadful security practice?

Better practice by far to have two processes; one with access to GPIO, one facing the web, with a suitable IPC mechanism between them.

My $0.02.
by tom.k.cook
Mon Apr 29, 2013 8:09 am
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

I got the sdhci-bcm2708 compiled with the upper called patches, but i can not mount the sd card. How could i debug where the error sits? I can modprobe the sdhci-bcm2708 module and the sdhci module. Tried to restart udev, but no events to see /dev/mmc* That's where I'm up to as well. Next step is t...
by tom.k.cook
Thu Apr 25, 2013 8:53 am
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

Yes, you are right, the sd card won't work. You need to put the root fs on something else - either usb or nfs. See my separate thread on how to get a booting kernel with PREEMPT_RT_FULL. Note that it's a booting kernel with the relevant configuration options enabled - the performance is far from wh...
by tom.k.cook
Tue Apr 23, 2013 9:17 pm
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

Yes, you are right, the sd card won't work. You need to put the root fs on something else - either usb or nfs. See my separate thread on how to get a booting kernel with PREEMPT_RT_FULL. Note that it's a booting kernel with the relevant configuration options enabled - the performance is far from wha...
by tom.k.cook
Thu Apr 11, 2013 9:01 pm
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

And, unfortunately, using cyclictest with either the wakeup or function tracers enabled (-W or -f or both) causes a kernel oops. It's too late to look into this tonight.
by tom.k.cook
Thu Apr 11, 2013 7:55 pm
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

Though having some clue about how to run cyclictest certainly helps: pi@raspberrypi ~/rt-tests $ sudo ./cyclictest -p95 -m # /dev/cpu_dma_latency set to 0us policy: fifo: loadavg: 0.08 0.08 0.05 2/141 2148 T: 0 ( 2148) P:95 I:1000 C: 11460 Min: 108 Act: 161 Avg: 148 Max: 529 Better, but still not br...
by tom.k.cook
Thu Apr 11, 2013 7:34 pm
Forum: Advanced users
Topic: CONFIG_PREEMPT_RT on Raspberry Pi
Replies: 88
Views: 49720

Re: CONFIG_PREEMPT_RT on Raspberry Pi

root@raspberrypi:/home/pi/rt-tests# ./cyclictest # /dev/cpu_dma_latency set to 0us policy: other/other: loadavg: 1.49 0.70 0.27 1/140 2048 T: 0 ( 2048) P: 0 I:1000 C: 31789 Min: 57 Act: 762 Avg: 167 Max: 4963 I'm just building a kernel with some tracers in it to try figure out what causes it. As a ...

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