Resource Note - Digital Serial Bus Technologies - I2C

In a context of digital electronics, a brief couple of resources bout the I²C serial bus protocol:

• Intefacing with the Linux kernel
• i2c-tools - I²C Tools for Linux
• libsoc
• Generic kernel interfaces
• ioctls
• Does not depend on i2c-tools
• See also 
• Benchoff, Brian.Speeding Up BeagleBone Black GPIO A Thousand Times. 2013
  
• Direct I/O onto /dev/mem to enable the SPI0 module clock, prior to GPIO I/O

• Blozis, Steve and Jean-Marc Irazaba. I²C Logic Family Overview . Philips. 2004
• Extensive presentation, even in its "slide format"
• Provides a thorough technical overview about I²C as a serial bus protocol
• Contains some useful "Best practice" advice, e.g. with a reference to the NXP P82B96 Dual bidirectional bus buffer

  

•  Blozis, Steve and Jean-Marc Irazaba. I²C Manual. Philips. 2003
• Provides an overview and comparison onto other serial bus protocols
• UART
• SPI
• CAN
• USB
• IEEE-1394 Firewire
• SMBUS
• A survey of individual connectors for cables in circuits using those protocols is available from Western Digital: WD Interface Guide (HTML)  (PDF)
•  Thorough explanation of theory and technology represented in the I²C serial bus protocol
• Observe that the I²C serial bus, in bidirectional bus operation, may be operated at one of three individual rates of clock timing -- maximum clock rates:
• 100 kbit/s (Standard-mode / Sm)
• 400 kbit/s (Fast-mode / Fm)
• 1 Mbit/s (Fast-mode Plus / Fm+
• 3.4 Mbit/s (High-speed mode / Hs-mode)
• In unidirectional bus operation, the bus may be operated in Ultra Fast-mode (UFm) at a maximum clock rate of 5 Mbit/s
• A multi-master I²C  protocol, effectively, would require a bidirectional mode of I²C bus operation

• Topic: Using I²C functions on contemporary single board computer platforms
• I²C on Raspberry Pi (RPi)
• Magda, Yury. Raspberry Pi Measurement Electronics: hardware and software. Second edition (Kindle). 2014
• uses i2c-tools (see previous items)
• Note that the RPi uses a Broadcom BCM2835 as a microcontroller munit (MCU). 
• Lacking further documentation about the I²C  interface(s) on the BCM2835 , the lack of availability of the BCM2835 data sheet may effectively serve to limit any I²C development on the RPi
• See also: Discussion in RPi forums
• Alternately: The BCM2835  may be found to publish interfaces for SPI and USB 2, as made avaialble via the RPi board. USB in particular is used on the RPi board.
•  I²C on the BeagleBone Black (BBB)
• PRU-ICSS modules on the TI Sitara MCU (ie. TI AM3358)
• See also: BBB - Working with the PRU-ICSS/PRUSSv2, Element 14 Community 
• Note: PRU-ICSS may be capable of only Standard-mode (100k) or Fast-mode (400k) I2C. See  Technical Reference Manual (AM335x) p. 4484 noting the specification of 100k or 400k
• Block view: Two PRU-ICSS modules in each TI Sitara MCU; One TI Sitara MCU to on each BBB. 
• See also: 
• System Refertence Manual (SRM) for BeagleBone Black. CircuitCo
• AM3358 Technical Documents. Texas Instruments.
• Data sheet for AM3358 
• Pinmux utility
• User Guide (AM335x) 13 pp.
• Note the section about interrupt events, including "INT_STS2_REG.GPIO_R/F_IT"
• Technical Reference Manual (AM335x) 1566 pp.
• Note specifically, sublcause 9 of the manual, Control Module through to subclause 9.2.2.1, Mode selection, concerning the two-bit MUXMODE field and its specifier values
• Note also subclause 4 of the manual, which is dedicated to the PRU-ICSS
• Note, thirdly, subclause 21.3.15 of the manual, How to Program I2C - using the PRU-ICSS function set
• For I²C development with the BBB and other TI Sitara (AM335x) platforms, it may be feasible to use the I²C features of one or both of the PRU-ICSS modules on the AM335x device, rather than reconfiguring the pimux of the primary ARM(R) Cortex A8 MCU via SYSBOOT
• References onto broader theory
• Bosworth, Edward L.  Introduction to Computer Organization (CPSC 2105). 2012
• Knight, Thomas, et al. CADR (MIT AI Memo 528)
• PRU-ICSS. Texas Instruments
• Hardware information (individual microcontrollers' product pages)
• Software information
• Getting Started Guide (PRU-ICSS)
• Recommends software packages for the development environment
• Code Composer Studio (CCS) v6
• See also: CCS for Sitara ARM
• NON-FREE (cf. DFSG)
• PRU Code Generation Tools (add-on, might be available via CCS UI)
•  PRU-SWPKG (see subsequent items) 
• Header files (PRU-ICSS) 
• PRU-ICSS Remoteproc Driver (Linux) (e.g LinuxLink RTOS on BBB)
• PRU-ICSS Rpmsg Driver (Linux) (e.g LinuxLink RTOS on BBB)
• See also: Linux EZ Software Devleopment Kit (EZSDK) for Sitara(tm) Processors . Texas Instruments
• NON-FREE (DFSG)  - Based on Code Composer Studio (CCS)
• Programmable Realtime Unit Software Development. Texas Instruments
• PRU Assembly Reference Guide
• PRU Assembly Instructions
• Notice the "Wait until bit set" and "Wait until clear" functions, each available for polling a status bit in a PRU register
• Advanced PRU Assembly Topics
• Debugging PRU Assembly Code
• PASM Tool
• PRU Linux Loader 
• Usage: Load assembler program into independent PRU memory area
• cf. PRU-ICSS Remoteproc driver (load time); see also: Rpmsg driver (runtime)
• See also: app_loader source code, beagleboard community
• PRU Software Support Package
• Specifically, the PRU-SWPKG edition (actively maintained) (x86 32 bit. For advice about installing 32 bit support on amd64 Ubuntu, see advisory note)
• PRU-SWPKG [Tools Platform]
• Depends on Code Composer Studio (CCS) [Tools Platform] a non-free component (cf. DFSG)
• PASM [Toolchain Component]
• FOSS (DFSG Compliant)
•  PASM (AM335X PRU) Source code available via beagleboard community at GitHub
• See also: LinuxLink embedded Linux Development Center for TI AM335x Sitara [Tools Platform, RootFS, Kernel]
• compatibility onto PASM - ?
• one of GNU libc / uClibc [compiler toolchain]
• Alternately, see also: Linaro Toolchain (BBB) (cf. TI EZSDK)
• A single PRU-ICSS module may provide access to an I²C bus, across the full range of available rates of clock timing in the I²C specification
• Driver support
• Integrating the PRU-ICSS within userspace software : ?
• Patching i2c-tools ? libsoc ?
• Integrating the PRU-ICSS within kernel drivers: 
• Module uio_pruss and BBB device tree updates
• See also, previous items (Remoteproc, Rpmsg drivers )
• Sitara Linux SDK
• Availability (???) see Linux EZ Software Devleopment Kit (EZSDK) for Sitara(tm) Processors  (???)  
• Refer to Release notes in ... ??? PRU-SWPKG ???
• ??? AM335x SDK BSP Source Code (???) 
• See also: BeagleBone PRU Notes, Embedded Linux WIki
• Accessing the  I2C interfaces (three available?) on the primary TI Sitara MCU module
• See also: BBB SRM
• Processor mode switching, Pinmux configuration
• uBoot
• Microinstructions for processor mode switch?
• SYSBOOT 
• See also: BeagleBone I2C2 Enable, Embedded Linux Wiki
• See also: Notes onto RTOS Linux, DSP42.
• Specifically, Timesys LinuxLink provides direct support for LinuxLink RTOS on the BeagleBone Black platform. Links and more are available at the other article

Notes – Serial Protocols

On one ambitious day, shortly ago, I'd found some resources in technical academia online, namely as with regards to serial "wire protocols" developed in digital electronics. I'd like to share that small part of my student notes outline, here, that I think I should wish to make reference to that outline, later on, and that this small outline could be of any interest to the arbitrary reader.

Ed. Note: I'd cut and pasted the following outline from within my own student notes, originally on a mobile tablet computer. I'd used the uxWrite app, on an iOS mobile tablet, for these notes. The uxWrite app, effectively, ensured that the text I'd copied from the uxWrite app was represented in Markdown format, when it was pasted into the 'blog entry, in the blogTouch app. A study of application cut/paste protocols would be left as an exercise to the reader, as would the reformatting of this outline into HTML format, immediately.

  - Serial Peripheral Interface (SPI)

      - “Three wire” protocol (Clock, SOMI, SIMO) \[eLinux:BBSPI\]

      - Microelectronics

  - UART, USART \[Durda\]

      - UART: Universal *Asynchronous* Receiver/Transmitter

      - USART: Universal *Synchronous-Asynchronous* Receiver/Transmitter

      - Synchronous Rx/Tx between single sender and single receiver

          - Clock signal provided by sender

          - “Strobe” signal

      - Asynchronous Rx/Tx

          - “Start bit”

      - As UART protocols \[Durda\] RS232, EIA232 \[Strangio\]

          - EIA232

              - Update of RS232

              - Conventionally, uses a modem interface

              - 22 pin (including ground) serial protocol with flow control and secondary data channel (e.g used for retransmit after parity error) using DB25 connectors

              - 9 pin (including ground) serial protocol with flow control, using DB9 connectors

  - PWM

  - I2C \[Magda\]

      - Multiple devices per I2C channel

      - “Two wire” protocol (SCL, SDA)

      - ***Compare***: TWI \[[Wikipedia](http://en.wikipedia.org/wiki/I%C2%B2C)\]

  - Serial ATA \[Lee\] (SATA)

      - 1.5 Gb/s, 3 Gb/s, 6 Gb/s

  - PCI Express \[Lee\] (PCIe)

      - PCIe 2 : 5 Gb/s

      - PCIe 3 : 8 Gb/s

Works referenced:

\[eLinux:BBSPI\] Embedded Linux Wiki. *BeagleBoard/SPI*. 2013. [Available (HTTP)](http://elinux.org/BeagleBoard/SPI). Accessed 9 May 2014

\[Durda\] Durda, Frank. *Serial and UART Tutorial*. 2014. [Available (HTTP)](https://www.freebsd.org/doc/en/articles/serial-uart/). Accessed 9 May 2014

\[Strangio\] Strangio, Christopher E. *The RS232 Standard, A Tutorial with Signal Names and Definitions*. 2012. [Available (HTTP)](http://www.camiresearch.com/Data_Com_Basics/RS232_standard.html). Accessed 9 May 2014

\[Magda\] Magda, Yury. *Raspberry Pi Measurement Electronics: Hardware and Software*. 2014. Kindle edition.

\[Palermo\] Palermo, Samuel. *High-Speed Serial I/O Design for Channel-Limited and Power-Constrained Systems*.

\[Lee\] Lee, Edward W. *High-Speed Serial Data Link Design and Simulation.*