Embedded systems

Recurring topics in `comp.arch.embedded`

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Embedded systems defined

An embedded computer is one that is 'embedded' inside another product. The end-user of the larger product may not even be aware that it contains a computer (though, ironically, many people have now heard of embedded systems from the Y2K hysteria).

Embedded systems are used in instruments and to control machinery. Devices around the home that may contain embedded controllers include:

Entertainment electronics: stereos, VCRs, televisions
PC: keyboard, keyboard controller, mouse, CD-ROM drive, hard drive, modem
Automatic setback thermostat
Telephone: answering machines, phones, cellular phones
Automobile: engine controller, stereo

Where are embedded systems tutorials/glossaries/FAQs?

http://www.Microcontroller.com/embedded/tutorials/tutorials.htm
http://www.netrino.com/Publications
http://www.landfield.com/faqs/microcontroller-faq/primer/
Embedded systems software: reentrancy, volatile data, etc: http://my.execpc.com/~geezer/embed/sw.htm

Magazines:

Electronic Engineering Times, a fascinating weekly: http://www.eet.com. Free to 'qualified' subscribers.
Circuit Cellar Ink: http://www.circellar.com. I don't know if it's possible to get this magazine for free.
Embedded Systems Programming (ESP): http://www.embedded.com They seem to be very particular about who gets the free subscriptions...

Chips

Programmable logic (PALs, GALs, FPGAs, PLDs)

http://www.latticesemi.com/lit/docs/datasheets/pal_gal/introgal.pdf
Getting started with programmable logic: http://www.geocities.com/leon_heller/pld_starter.html

Ethernet chips for embedded systems

Cirrus CS8900A 8-/16-bit Ethernet controller
- PDF data sheet: http://www.cirrus.com/pubs/8900a.pdf
SMSC LAN91C96 8-bit Ethernet controller: http://www.smsc.com/main/catalog/lan91c96.html
SMSC LAN91c111 for 10/100 Mbps. This chip "draws a lot of power (>200 mA) and gets really hot."
ASIX Ax88796: 100 Mbps Ethernet chip for embedded systems. NE2000-compatible, 10 or 100 Mbps, 3.3v (5v tolerant), LQFP-128. http://www.asix.com.tw/products/Ax88796.htm, http://www.circuitcellar.com/library/print/1002/eady147/index.htm

Modems for embedded systems

Consider connecting an internal 8- or 16-bit ISA PC modem to your embedded system. Such a modem is already FCC-approved and, as a consumer device, is cheap.
Silicon Labs SI3044 chipset (DAA only?)
Motorola MC145442/MC145443 (300 baud single chip) is no longer available
SI2400 (replaces Motorola MC145442/MC145443; can also run at 2400 bps?)
Texas Instruments 74HC942 and 74HC943 are no longer available. IST makes a pin-compatible chip called the SC11002.
RC224ATF single-chip 2400 bps modem: http://www.ustr.net/modem/index.shtml
SDK for Motorola DSP56800(E) contains assembly-language source code for a modem
V.23 modem implemented in software using MSP430 CPU: http://www.gaw.ru/pdf/TI/app/msp430/slaa037.pdf
'We made a 2400 modem for under $30 using this': http://www.zilog.com/products/partdetails.asp?id=Z02201 (V.22bis [2400 bps], full duplex)

On-screen displays (OSD)

http://www.circuitcellar.com/pastissues/articles/Baptiste112/text.htm

Algorithms

Simple serial network protocols

Win95 HyperTerm is crap; try TeraTerm Pro instead (yes; it's free)
9-bit networking with PC serial port: you can use the parity bit as the 9th bit, but receive and transmit must be POLLED
Controller Network Protocol: www.certsoft.com/cnp11.pdf
HDLC usually needs synchronous (bit-oriented) serial ports, but here is an implementation of HDLC over async serial ports: http://microtrol.com.au/hdlc.htm. See also PPP.
PPP: see RFC-1171: http://www.rfc-editor.org/rfc/rfc1171.txt
Serial Network Protocol for embedded systems: http://www.rdos.net/sernet/index.htm

Memory testing

Beware the capacitance of a floating bus. Does your memory test pass if there's no RAM chip in the socket?
Beware of aliasing caused by unconnected high-order address lines.
What exactly are you testing: the memory chips or the wiring from the CPU to the memory chips?
Software-Based Memory Testing by Michael Barr: http://www.netrino.com/Articles/MemoryTesting/paper.html

Data validation:

Parity detects single-bit errors.
CRC detects multibit errors.
- CRC intro: http://www.repairfaq.org/filipg/LINK/F_crc_v3.html
- CRC code in PIC assembly language: http://www.repairfaq.org/filipg/LINK/F_crc_uP.html
- http://www.ross.net/crc/crcpaper.html
Forward error correction (FEC) not only detects the errors, but fixes them.
- Reed-Solomon codes: http://www.4i2i.com/reed_solomon_codes.htm
- ECC resources: http://www.ee.umn.edu/users/jchen/ecc.html
- Error-correcting codes: Reed-Solomon, BCH, CRC, Turbo, Viterbi: http://www.eccpage.com/

Data compression

Various compression schemes with source code: http://www.data-compression.com/index.shtml
zlib: http://www.info-zip.org/pub/infozip/zlib/
LZO, lzop, NRV, and UPX: http://www.oberhumer.com/mfx/
LZSS decompression is very simple. An LZSS variant compatible with Microsoft COMPRESS/EXPAND: http://my.execpc.com/~geezer/software/lzss.zip
The patent on LZW expired on June 21, 2003 in the USA. In other countries, it expires on June 21, 2004.

Pseudo-random numbers

Linear-feedback shift register (LFSR): http://my.execpc.com/~geezer/embed/random.htm

'what's a Von Neuman compensator?'

        Take a biased stream of 1's and 0's two at a time.

        If the pair is 00, do nothing.
        If the pair is 01, output a 0.
        If the pair is 10, output a 1.
        If the pair is 11, do nothing.

        (some implementations switch the outputs so that 01 = 1 on odd
        cycles and 01 = 0 on even cycles.  The hardware random number
        generator on Intel's latest motherboards uses this method.)

        a Von Neuman compensator will remove the biases caused by switching
        threshholds that are not exactly at 50%, and other biases common to
        the analog to digital stages in typical hardware random number
        generators, and will also remove the biases caused by asymmetrical
        duty cycles and other biases common to typical counter/timer based
        random number generators.

CORDIC

CORDIC (COrdinate Rotation DIgital Calculation) is an iterative way to calculate trig functions. Unlike a Taylor series, only shifts and adds are used. Typically, you iterate (pass through a software loop) once for each bit of precision in the result.

Implementing Sine on the PIC: http://www.brouhaha.com/~eric/pic/sine.html
CORDIC bibliography: http://www.taygeta.com/cordic_refs.html
CORDIC tutorial: http://my.execpc.com/~geezer/embed/cordic.htm

Safety

In this context, 'safety' means safe operation of the system run by an embedded controller. It does not refer to language features (such as garbage collection, no pointers, or strong typing) that make it easier to produce correct code.

Some organizations have created guidelines for improving the reliability and/or safety of embedded system software:

MISRA Guidelines for the Use of the C Language in Vehicle Based Software: http://www.misra.org.uk/misra-c.htm
Safety Management Requirements for Defence Systems: Def Stan 00-56: http://www.dstan.mod.uk
IEC 61508: http://www.iec.ch
Software Considerations in Airborne Systems and Equipment Certification: RTCA DO-178B: http://www.rtca.org
Niall Murphy's Pages on software safety: http://www.panelsoft.com/safety.htm

Miscellaneous/other

File formats (including HEX and S19)

http://www.wotsit.org

Flash memory

Open-Source wear-levelling filesystem for flash memory? http://www.linux-mtd.infradead.org/

flash memory:
can solder blank chip to board if:
- Motorola 6811 with boot-from-serial-port mode
- Motorola MPC8xx with BDM (background debug mode)
- other processors (which?) with JTAG port (JTAG is slow)
- non-Harvard CPU architecture (code and data in one address space;
  so update code can run in RAM while Flash is being updated)

Small/free TCP/IP stacks

Liquorice: http://liquorice.sourceforge.net/ Scalable RTOS with networking, written mostly in C. AVR and 386 CPUs. LGPL-ish license. SLIP, PPP, ARP/Ethernet, ICMP, UDP and TCP.
LWIP: http://www.sics.se/~adam/lwip/ IP, ICMP, UDP, TCP. Socket API. DJGPP, uC/OS, eCos, and Rabbit 2000 ports.
UCIP: http://ucip.sourceforge.net/ BSD license.
Watt-32: http://www.bgnett.no/~giva/
OpenTCP: http://www.opentcp.org/ Supposedly written in ANSI C. BSD-like license.
Phil Karn's KA9Q TCP/IP code: http://www.ka9q.net/code/ka9qnos/ Various copyrights, but the PPP code is public domain.

Recurring topics in comp.arch.embedded