Raspberry Pi HAT offer NMEA 2000 link for marine applications

Copperhill’s $99 “PiCAN-M” HAT for the Raspberry Pi provides CAN-based NMEA 2000 and RS-422 driven NMEA 0183 ports for marine applications. The HAT includes a 3A SMPS supply and a Qwiic link. In 2019, Copperhill Technologies launched a PiCAN3 CAN-Bus HAT for the Raspberry Pi 4. The new PiCAN-M (for Marine), built for Copperhill by SK Pang, offers a marine-specific, NMEA 2000 compatible version of CAN. The $98.50 HAT also supplies an RS-422-based NMEA 0183 interface plus a Qwiic interface for adding SparkFun’s Qwiic add-ons.

How a Linux migration led to the creation of Amazon Web Services

Dan Rose, chairman of Coatue Ventures and Coatue Growth, posted a thread on Twitter the other day, 280 characters or less at a time, in which he chronicled how it came about that AWS infrastructure is built on Linux. Rose was at Amazon from 1999 to 2006, where he managed retail divisions and helped incubate the Kindle reader before moving to Facebook. So he was at Amazon in 2000 when the internet bubble popped,and one high-flying dot-com after another was shriveling up and dying, having burned through ridiculous amounts of capital on luxurious offices while often having nothing by way of a product to show for it. Rose said Amazon’s biggest expense was the data center outfitted with expensive Sun servers. Amazon’s motto was “get big fast,” and site stability was critical. Every second of downtime meant lost sales, and Sun was the gold standard for internet servers back then. I can recall them having a significant software business led by a VP named Eric Schmidt.

Kernel: Restricted DMA and AMD Work in Linux 5.11

• Restricted DMA

  A key component of system hardening is restricting access to memory; this extends to preventing the kernel itself from accessing or modifying much of the memory in the system most of the time. Memory that cannot be accessed cannot be read or changed by an attacker. On many systems, though, these restrictions do not apply to peripheral devices, which can happily use direct memory access (DMA) on most or all of the available memory. The recently posted restricted DMA patch set aims to reduce exposure to buggy or malicious device activity by tightening up control over the memory that DMA operations are allowed to access. DMA allows devices to directly read from or write to memory in the system; it is needed to get reasonable I/O performance from anything but the slowest devices. Normally, the kernel is in charge of DMA operations; device drivers allocate buffers and instruct devices to perform I/O on those buffers, and everything works as expected. If the driver or the hardware contains bugs, though, the potential exists for DMA transfers to overwrite unrelated memory, leading to corrupted systems and unhappy users. Malicious (or compromised) hardware can use DMA to compromise the system the hardware is attached to, making users unhappier still; examples of this type of attack have been posted over the years. One way to address this problem is to place an I/O memory-management unit (IOMMU) between devices and memory. The kernel programs the IOMMU to allow access to a specific region of memory; the IOMMU then keeps devices from straying outside of that region. Not all systems are equipped with an IOMMU, though; they are mostly limited to the larger processors found in desktop machines, data centers, and the like. Mobile systems usually lack an IOMMU.

 

• A Fix Has Been Proposed For The Slower AMD Performance On Linux 5.11

  With the in-development Linux 5.11 kernel there are many great features and improvements especially for AMD users with some new drivers and other pleasant enhancements. But as I outlined back on Christmas day: Linux 5.11 Is Regressing Hard For AMD Performance With Schedutil. Fortunately, a fix is now en route to the Linux 5.11 kernel for fixing that performance regression affecting AMD Zen 2/3 desktops and servers.  As outlined in that original article after bisecting the sizable performance regressions and in follow-up tests, AMD hardware performing slower on Linux 5.11 came down to the CPU frequency invariance support introduced this cycle and is utilized by the "Schedutil" CPU frequency scaling governor. With Schedutil often being the default for AMD systems on newer versions of the Linux kernel, this regression on Linux 5.11 compared to prior kernel releases has been unfortunate. 

• Linux 5.11 Is Now Looking Great For AMD Zen 2 / Zen 3 Performance - Phoronix

  Not only is the AMD "CPU frequency invariance regression" from that new support with the in-development Linux 5.11 kernel on course to address the performance shortcomings I outlined last month, but with the patched kernel for a number of workloads the performance is now ahead of where it was at with Linux 5.10.