Raspberry Pi 3 + UART/Bluetooth issues

Raspberry Pi 3 + UART/Bluetooth issues

• 1.
  Raspberry Pi 3+ UART/Bluetooth Issues By: Yeo Kheng Meng ([email protected])Hackware v1.6 (30 Mar 2016) 1 Video of my presentation can be found here: • https://engineers.sg/video/raspberry-pi-3-uart-bluetooth-issues--609
• 2.
  Whats new? (Features) SpecificationsRaspberry Pi 2 Raspberry Pi 3 CPU BCM2836 Cortex-A7 900Mhz ARMv7 BCM2837 Cortex-A53 1.2Ghz ARMv8 (64-bit) GPU 250Mhz Videocore IV 1080p,30FPS,H.264 video decoding 400Mhz Videocore IV 1080p,60FPS,H.264 video decoding Wifi - 802.11n, 2.4Ghz only, single stream 150Mbps Bluetooth - Bluetooth 4.1 (Dual-mode) Classic and BLE 2http://raspi.tv/2016/raspberry-pi-3-model-b-launches-today-64-bit-quad-a53-1-2-ghz-bcm2837
• 3.
  Whats new? (Board) SpecificationsRaspberry Pi 2 Raspberry Pi 3 LED positions Top left Bottom left microSD storage Spring No Spring 3
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  UART (Debug console)issues on RPi 3 4
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  UART Debug Console + USB-TTLcable https://www.adafruit.com/product/954 • Universal asynchronous receiver/transmitter 5
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  UART (Serial Debugconsole) issue Received output. • Garbled or nothing • Output is 72000 instead of 115200 baud Expected output 6
• 7.
  Hardware architecture (≤RPi 2) System on Chip BCM2835 (RPi 1 B/B+) / BCM2836 (RPi 2) • BCM283x has 2 UARTs • UART0: Full UART (/dev/ttyAMA0) • Based on ARM Primecell PL011 • Larger FIFO buffers • 16x8 transmit • 16x12 receive • High performance full feature serial port • Older RPi models breaks out UART0 to the pin header • Default use: Debug console • UART1: “mini UART” (/dev/ttyS0) UART0 UART1 BCM2835 datasheet: Page 10 https://www.raspberrypi.org/wp-content/uploads/2012/02/BCM2835-ARM-Peripherals.pdf 7
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  System on Chip BCM2837(RPi 3) Hardware architecture (RPi 3) SDIO BCM43438 wireless chip http://raspi.tv/2016/raspberry-pi-3-model-b-launches-today-64-bit-quad-a53-1-2-ghz-bcm2837 Bluetooth 4.1Wifi 8 • UART0: Full UART (/dev/ttyAMA0) • UART1: “mini UART” (/dev/ttyS0) UART1 UART0
• 9.
  Why is UART1a problem? BCM2835 datasheet: Page 10- 11 https://www.raspberrypi.org/wp-content/uploads/2012/02/BCM2835-ARM-Peripherals.pdf 9 Note: I use BCM2835 datasheet as datasheets of newer chips have not been released by Broadcom. Mini UART implementation should be the same across BCM283x. Problem Explanation • 𝑏𝑎𝑢𝑑𝑟𝑎𝑡𝑒 = 𝑐𝑜𝑟𝑒𝐹𝑟𝑒𝑞 8 ∗(𝑏𝑎𝑢𝑑𝑅𝑎𝑡𝑒𝑅𝑒𝑔+1) • RPi 3 boot time core frequency is 400Mhz • RPI baud rate default 115200 • 115200 = 400 000 000 8 ∗ (𝑏𝑎𝑢𝑑𝑅𝑎𝑡𝑒𝑅𝑒𝑔+1) • baudRateReg calculated on core frequency retrieved at boot time • Frequency scaling, may drop to 250Mhz to save power under low load • Fluctuating core frequency -> Fluctuating baud rate
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  Who is affected? Anyonewho uses the TX/RX header pins • People who use the serial debug console • Headless systems • RPi shields that uses the UART • Eg. RS232, GPS/GSM • Device-Device communication to other MCUs or MPUs • Require high UART performance (aka full UART) and Bluetooth 10
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  How do wesolve this? Part (1/2) Lock a constant core frequency during boot time • (For old firmware) Add “core_freq=250” XOR “force_turbo=1” to /boot/config.txt • Lock core core_freq to minimum or maximum (400Mhz) respectively • Minimum -> RPi 3 performance will be affected. • Maximum -> Requires good cooling. • Can still be throttled to 250 Mhz under low voltage or high temperature conditions • (For new firmware) Add “enable_uart=1” to /boot/config.txt • All RPi distributions will eventually support this option going forward • Similar to “core_freq=250” with clearer intent • Raspbian latest stable updates does not support this yet • Need bleeding-edge firmware update: “sudo apt-get install rpi-update” & “sudo rpi-update” • Arch Linux requires an update to use this option: Just use “pacman –Syu” • Distros that support this option will disable debug console if “enable_uart=1” is not set • “enable_uart=1” explanation Raspberry Pi Foundation Engineer Phil Elwell (pelwell) • https://github.com/raspberrypi/firmware/issues/553#issuecomment-199486644 11
• 12.
  How do wesolve this? Part (2/2) Remap header pins to use Full UART with device tree overlay (pin-crossbar) • Add “dtoverlay=pi3-disable-bt” to /boot/config.txt • Disables Bluetooth in the process as UART1 is unconnected • Requires extra “sudo systemctl disable hciuart” for Raspbian • Or add “dtoverlay=pi3-miniuart-bt” to /boot/config.txt • Bluetooth now uses mini-UART • Need to add “core_freq=250” or “force_turbo=1” to /boot/config.txt so Bluetooth via mini UART is usable • Edit “/lib/systemd/system/hciuart.service” and replace “ttyAMA0” with “ttyS0” for Raspbian • Bluetooth’s performance will be affected. Only low- throughput BLE may be effectively usable. • If any of these options are used, the serial console will be enabled unless “enable_uart=0” 12 System on Chip BCM2837 (RPi 3) SDIO BCM43438 wireless chip Bluetooth 4.1Wifi • UART0: Full UART (/dev/ttyAMA0) • UART1: “mini UART” (/dev/ttyS0) UART0 UART1
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  Solution summary Set in/boot/config.txt • Serial console and normal Bluetooth • Lock frequency • Old: “core_freq=250” XOR “force_turbo=1” • New: ”enable_uart=1”. Add “force_turbo=1” to lock at high frequency. • High performance Serial • Switch UART0 and UART1 pins • No Bluetooth • “dtoverlay=pi3-disable-bt” • (Raspbian) Run “sudo systemctl disable hciuart” • Slow Bluetooth Classic or BLE • “dtoverlay=pi3-miniuart-bt” AND (“core_freq=250” XOR “force_turbo=1”) • (Raspbian) Edit “/lib/systemd/system/hciuart.service” and replace “ttyAMA0” with “ttyS0” • Add “enable_uart=0” to disable debug console • The use of the mini UART will always require locking of Core frequency 13
• 14.
  Arch Linux Bluetooth’sissues • Raspbian uses “pi-bluetooth” to provide Bluetooth features • “pi-bluetooth” has not been ported to Arch Linux • Someone has posted a temporary package to AUR • https://archlinuxarm.org/forum/viewtopic.php?f=67&t=10017s • https://aur.archlinux.org/packages/pi-bluetooth/ • My setup instructions using that package • https://gist.github.com/yeokm1/d6c3ca927919c61257cd 14
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  Useful links 1. BCM2835datasheet: https://www.raspberrypi.org/wp-content/uploads/2012/02/BCM2835-ARM-Peripherals.pdf 2. Original Github issue: https://github.com/raspberrypi/firmware/issues/553 3. “enable_uart=1” explanation by Raspberry Pi Foundation Engineer Phil Elwell https://github.com/raspberrypi/firmware/issues/553#issuecomment-199486644 4. UART DT overlays: http://www.briandorey.com/post/Raspberry-Pi-3-UART-Boot-Overlay-Part-Two 5. Detailed DT overlays: https://github.com/raspberrypi/linux/blob/rpi-4.1.y/arch/arm/boot/dts/overlays/README 6. Arch Linux ARM Bluetooth forum issue thread: https://archlinuxarm.org/forum/viewtopic.php?f=65&t=9961 7. Instructions to enable Arch Linux Bluetooth: https://gist.github.com/yeokm1/d6c3ca927919c61257cd 15