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[Lcdproc] Strangeness with BIGNUMs on 2x20 display

Chronological Thread 
  • From: ethan.dicks at (Ethan Dicks)
  • Subject: [Lcdproc] Strangeness with BIGNUMs on 2x20 display
  • Date: Tue, 16 Sep 2008 04:35:02 +0000

Hi, All,

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},
{" "},
{" "}},

There's a '7' in the top right spot. That seems odd because further
down in the code, it _definitely_ sets chars 0-5...

for (i = 0; i < 6 ; i++) { // put the customcharacters
into the display
drvthis->set_char(drvthis, offset+i, bignum[i]);

I have not worked with 2-line displays much. Can anyone provide any
historical perspective for this code issue? Was this code originally
designed for a display with 8 soft chars and not completely dumbed
down? Are there any displays with 6 or 7 but not 8 soft chars (or was
this an attempt to leave the heartbeat slot alone)?

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.


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