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[lcdproc] crystal fontz SPI over parallel

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  • From: tse AT (Benjamin Tse)
  • Subject: [lcdproc] crystal fontz SPI over parallel
  • Date: Fri, 10 Mar 2000 09:42:44 +1100

Hi Andrew,

On Thu, Mar 09, 2000 at 03:18:38PM +0800, EXT McMeikan, Andrew wrote:
> my assumption #1. The data sent via SPI is the same data stream that would
> normally be sent by RS-232

This is me being pedantic :-) ... It is the same data that is sent to
the _serial port_. The stuff over RS-232 includes framing. The SPI bus
also has a separate clock. This all looks like your 4094
implementation :-).

> my assumption #2. The lcdproc code normally sends this data to
> /dev/serial-port-of-choice and could be made to pipe it instead

I suppose so ... output to the serial port could be sent to something
that spits it out the parallel port instead.

> my proposed way to do it (quick cheap, code over the weekend way): write a
> small no brainer program that reads an input stream and sends the data out
> the parallel port in SPI format as fast as it can (max of 18kbaud/ 55uS clk
> period {oh no yet more CPU/nanosleep wars})

Brent's code is rather conservative, if you look at the CFontz web
page you'll find that you can dispense with most of his timings. Thus
reducing the extra load.

> Flame suit: I know this isn't the most ideal way, but if no one objects I'll
> have the stand alone code done for Monday and then Sean can have his display
> up and anyone who cares can optimize it or re-write it as they feel later.

It's the fastest way of getting Sean's problem solved. Just as long as
we don't have to live (too long) with the results of bad design caused
by coding on the run.

The (next) hardest part is to include support for the other 7
displays. The HD44780 parallel port modules support this, but this
isn't necessarily the best place for it.


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