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[Lcdproc] Strangeness with BIGNUMs on 2x20 display

Chronological Thread 
  • From: peter at (Peter Marschall)
  • Subject: [Lcdproc] Strangeness with BIGNUMs on 2x20 display
  • Date: Tue, 16 Sep 2008 16:47:22 +0200

Hi Ethan,

On Tuesday, 16. September 2008, Ethan Dicks wrote:
> Working with Nicu to get around some issues with a picoLCD 2x20, I've
> run into a problem that looks to be in the BIGNUM library.
> Based on the performance characteristics of my LCD, lib_adv_bignum()
> has correctly identified it as having "6 or more" soft chars. The
> display I get for "6", for example, though, has a garbage character on
> the top right. Checking the pattern...
> {{3 ,5 ,7},/*6*/
> {3 ,4 ,2},
> {" "},
> {" "}},

Right, the 7 is definitely wrong.
When we have only 6 custom characters counted 0 - 5,
then 7 is off by two.

The code for this function was provided as a whole
(including the error).

Looking at the defined shapes, and the definition
of the 5 remainig characters, I changed the 7 to a
space (' '). This makes the horizontal line on the
top of 6 similar to the one for 5.

Fix is already committed to CVS.

Thanks for reporting the issue.

> I found this while tracking down a different problem - with this
> driver, there seems to be a problem sending a character 0x00 in the
> data stream. Normally this isn't seen, but it is with BIGNUMs. I
> have been over picolcd.c, and there doesn't seem to be any obvious
> place that the code is stopping early because of a null character in
> the data stream, and likewise, I've been over the code in usblib
> 0.1.12 and not found anything exceedingly obvious, but the behavior
> nonetheless points to *some* bit of code stopping at a null.
> I'm not seeing the same behavior (i.e., BIGNUMs not working because of
> the use of 0x00) with MtxOrb, 44780-usb4lcd, or my own
> as-yet-unreleased jw002 driver. In terms of transport-layer code,
> MtxOrb and jw002 are serial, and 44780-usb4lcd is USB, but that one
> uses a completely different method of talking to the display than
> picoLCD, so that should help narrow down the search.
> Is anyone else fiddling with BIGNUMs? This is far from the first
> message I've posted recently on the topic, and I've gotten very little
> response previously.

Sorry for not answering earlier.
RL has kept me busy.


Peter Marschall
peter at

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