Bit-banging I2C

On 3/17/2016 11:12 AM, Tim Wescott wrote:
>
> Yes, more or less.

A teacher in high school would never let us answer that way.  "Which is 
it, more or less?"

-- 

Rick

On Fri, 18 Mar 2016 02:12:00 -0400, rickman wrote:

> On 3/17/2016 11:12 AM, Tim Wescott wrote:
>>
>> Yes, more or less.
> 
> A teacher in high school would never let us answer that way.  "Which is
> it, more or less?"

Well, then they need to get a real job and discover ambiguity.

-- 

Tim Wescott
Wescott Design Services
http://www.wescottdesign.com

On 3/18/2016 1:55 PM, Tim Wescott wrote:
> On Fri, 18 Mar 2016 02:12:00 -0400, rickman wrote:
>
>> On 3/17/2016 11:12 AM, Tim Wescott wrote:
>>>
>>> Yes, more or less.
>>
>> A teacher in high school would never let us answer that way.  "Which is
>> it, more or less?"
>
> Well, then they need to get a real job and discover ambiguity.

Lol.  I think you are showing some ignorance.  If you think a teacher 
should encourage kids to speak ambiguously you definitely are not 
qualified for teaching.  I think few in this business would be good 
teachers... especially if they feel teaching is not "a real job".

His point was this was what he called, "waffle words" which are used to 
reduce the significance of what was being said.  Better to find ways of 
speaking to emphasize what was being said.

This all had no impact on many of the kids who had little interest in 
learning, but I learned a lot from his teaching methods.

-- 

Rick

On 16/03/2016 2:49 PM, Tim Wescott wrote:
> Has anyone successfully bit-banged an I2C interface?  Any comments on
> it's ease or difficulty?
>
> I've used I2C with processors that have built-in hardware, I've sat next
> to a guy who's bit-banged it, but I've never bit-banged it myself.
>
> I ask as a circuit designer who's going to design in an I2C chip to be
> presented to a software engineer with a smile and a "here, this ought to
> be easy!"  I want to know whether I'll be honest or not.
>


It is pretty easy. Read the spec think about it over night, a couple 
hours to implement and test. What we have found is we run across devices 
that don't always implement I2C protocols.

w..

In article <hoKdnRCiZNQBN3TLnZ2dnUU7-TOdnZ2d@giganews.com>, 
seemywebsite@myfooter.really says...
> 
> Has anyone successfully bit-banged an I2C interface?  Any comments on 
> it's ease or difficulty?
> 
> I've used I2C with processors that have built-in hardware, I've sat next 
> to a guy who's bit-banged it, but I've never bit-banged it myself.
> 
> I ask as a circuit designer who's going to design in an I2C chip to be 
> presented to a software engineer with a smile and a "here, this ought to 
> be easy!"  I want to know whether I'll be honest or not.

Most code and testing of interface (with full timing and checking 
basic reading/writing device) for compliance worst case 2 days on a 
hardware mock up on a Eval board with a sample device.

Anything beyond that is problems due to MCU and/or device specification
'issues', or lack of understanding. Assuming you have already worked out
how to use the MCU in question.

Having done all forms of I2C and SPI as from MCU hardware controllers, 
NXP I2C controllers, FPGA master and slave devices, software bit bang on 
MCU's and even back in day from PC printer port using Windows for 
Workgroups. 

One device was FPGA EEPROM emulator capable of I2C over 2MHz.

Many other have posted many things to look at out far I would add

1/ reset on device, if Software bit banging have a way of resetting the
   device whether SPI or I2C, when software bit banging nothing like
   debug, actual bug, or even whilst uploading new code to screw up 
   random clock sequences. Having debugged many devices.

2/ Making sure device can work with irregular clock drive, so many 
   devices fail when they expect an exact regular clock. I2C and SPI do
   NOT need an exact clock as they are stateful bit operations.

3/ Will device do proper reset from 9 clock pulses and stop condition
   I2C spec reset many devices fails.

4/ Any software should check the ACTUAL pin voltages as often as 
   possible even with one device a shorted I2C or SPI pin is a pain.

5/ Does your device nee an I2C Restart state which is slightly different
   to Start and make sure software/hardware can cope with it.

There are plenty of software bit bang examples I2C and SPI around as 
starting point. Plenty also of FPGA code. I have always reviewed these
examples as often they are lacking, but a good staring point.

Having dealt with many devices generally I2C is easier, many issues
with SPI controllers ranging from only do bytes or multiples, screwing
up Chip selects, getting byte orders to match.....

-- 
Paul Carpenter          | paul@pcserviceselectronics.co.uk
<http://www.pcserviceselectronics.co.uk/>    PC Services
<http://www.pcserviceselectronics.co.uk/pi/>  Raspberry Pi Add-ons
<http://www.pcserviceselectronics.co.uk/fonts/> Timing Diagram Font
<http://www.badweb.org.uk/> For those web sites you hate

Tim Wescott wrote:
> On Fri, 18 Mar 2016 02:12:00 -0400, rickman wrote:
>
>> On 3/17/2016 11:12 AM, Tim Wescott wrote:
>>>
>>> Yes, more or less.
>>
>> A teacher in high school would never let us answer that way.  "Which is
>> it, more or less?"
>
> Well, then they need to get a real job and discover ambiguity.
>


Well... maybe.

-- 
Les Cargill

On Wednesday, March 16, 2016 at 5:10:36 PM UTC-7, Clifford Heath wrote:
> On 17/03/16 05:49, Tim Wescott wrote:
> > Has anyone successfully bit-banged an I2C interface?  Any comments on
> > it's ease or difficulty?
> >
> > I've used I2C with processors that have built-in hardware, I've sat next
> > to a guy who's bit-banged it, but I've never bit-banged it myself.
> >
> > I ask as a circuit designer who's going to design in an I2C chip to be
> > presented to a software engineer with a smile and a "here, this ought to
> > be easy!"  I want to know whether I'll be honest or not.
> 
> Not I2C, but I've bitbanged One-Wire, including enumeration (though not 
> high-speed), in an MSP430. I assume this relates to your battery gauge 
> question? If so, I'd think One-Wire was preferable - only one pin to diddle.

So, we are trying to do one-wire with a PC class (linux) master and FPGA slave.  The master has file system I/O interface.  We can do the protocol as slow as possible.
 
> However, to get bit timings right, the important question is whether you 
> can afford to stop the world while doing a data transfer. Trying to 
> interrupt for each bit transition might be too hard. I guess you 
> wouldn't need to read the gas gauge very often - perhaps you can pick a 
> time when you can lock out all other interrupts?

Yes, we will have to disable interrupts a few msec at a time.