JP1 Remotes

jmezz13 · Joined: 28 Oct 2004 Posts: 94

I've been diving into more of the details of IR code protocols, and I just read a bit about (RM) Protocol Builder.

This is probably a silly oversight on my part, but I've read the Infrared Protocol Primer and done some manual decodes using IRScrutinizer and I thought I understood how the burst pairs are coded. Then I opened up RMPB and loaded the NEC1 protocol and noticed it is implying (PD04 through PD09) that the logical one burst pair is +560, -564 and the logical zero is +560, -1690. That is reversed from what the IR Primer says and what I found decoding in IRScrutinizer where the 0's have a 1:1 ratio and 1's have a 1:3 ratio.

What concept am I mssing?

The Robman · Posted: Mon Feb 27, 2023 6:32 pm Post subject:

Deciding which pair is logical 1 vs 0 is all a matter of perspective. When we capture the signals from a protocol for the first time, we usually sort them by function name, so the numeric buttons are all in order, then we look at the binary and decide what makes sense. If the binary appears to increment on the left, we call it LSB, if it increments on the right, we call it MSB. If the binary for the numeric buttons appears to be large numbers descending, then we probably got the 0/1 decision wrong.

For NEC, the big pair is 1 and the small pair is 0.

Most UEI executors get the 0/1 pairs reversed (in our opinion), so we call those COMP. Therefore, the UEI executor for NEC is LSB-COMP. Keep in mind that UEI doesn't really care if they get it right or wrong because they don't bother to derive OBCs from the captures because they're not going to try to find secret discrete codes. They will simply supply the right hex codes to their executors in order to re-create the signal that they captured.
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jmezz13 · Joined: 28 Oct 2004 Posts: 94

Thanks Rob. I had to take a minute or two to wrap my head around your response.

I hadn't seen the LSB-Comp before, but since you mentioned it, although subtle, I now see it in the RMPB (Device Data) and in the PB spreadsheet.

I guess it boils down to a convention that the JP1 community uses for coding that doesn't have to make sense to the processors in the remote since there are translators in the middle making appropriate conversions.

Jay

The Robman · Posted: Tue Feb 28, 2023 12:30 pm Post subject:

Right, we try to get into the minds of the guys who invented the protocol, or who created the original remote, which is something that UEI has no need to do. We do it because it helps us give meaningful code numbers to the data, and helps us spot gaps which might be for secret codes.
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Barf · Posted: Tue Feb 28, 2023 1:20 pm Post subject:

As Rob says, there is a certain element of arbitrariness when selecting what the duration pairs are assigned to what code, the selection of the bit order of the data, and how the bits are grouped together in parameters. The first and foremost priority should always be to be as compatible to the rest of the world, in particular official documentation, to the extent it exists. Unfortunately, there are other people who makes other choices. A good example is the first version of the "IRremote" library for the Arduino, written by Ken Shirriff. While "we" use three 8-bit parameters in lsb-first order (the fouth parameter is almost always the complement of the third), Shirriff just took it as one 32 bit word, in msb-first order. (This is available as the protocol NEC-Shirriff-32.)

My advice is to (superficially) try to learn to read IRP notation. You can send any signal you want with IrScrutinizer + your Arduino.

jmezz13 · Joined: 28 Oct 2004 Posts: 94

The Robman · Posted: Tue Feb 28, 2023 8:02 pm Post subject:

The main assembler used here is Samsung S3C8, we've been able to do some pretty cool stuff with it.
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jmezz13 · Joined: 28 Oct 2004 Posts: 94

The Robman · Posted: Wed Mar 01, 2023 9:54 am Post subject:

A while back now, when people still used DVD players, there was an Apex player which didn't have dedicated arrow buttons, I think the number pad doubled as the arrow pad (where 1=up, 4=left, 5=OK, 6=right, 8=down) but you had to hit SHIFT first, and people didn't like it. So I checked the full list of button codes to see what range of OBCs was used and I think they were all below 128, which meant that the MSB of the binary was available. So, I wrote some code where, if the MSB was set, the executor would send the SHIFT signal, followed by the OBC entered (with the MSB unset), followed again by SHIFT. Then in the upgrade, all you had to do to get true arrow buttons was add 128 to the OBC for the arrow buttons.

Then, back when ReplayTV was still around, we discovered that if you press a numeric button followed by the SKIP button, the program would jump ahead by that many minutes. So I found an unused bit in the binary, probably the MSB like with the Apex code, and if it was set, the executor would send the given binary with the MSB unset, followed by SKIP. Therefore, to create a 3-minute-skip button, perfect for jumping over commercials, you would just add 128 to the OBC for the "3" button. We did a bunch of other stuff for ReplayTV, but I'm forgetting what now.

Then there was the Sony DSP, which sent a 5 or 6 part signal, which was almost impossible for remotes to properly learn, but fortunately we were able to get enough good learns to figure it out, so we wrote an executor to replicate that one.

There are many devices that use a combination of device codes for a single device, so we've written combo executors for those that let you mix and match your device codes.

And that's not even mentioning the Device Combiner and all the extenders, which are also written in assembler. Pretty cool, eh?
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jmezz13 · Joined: 28 Oct 2004 Posts: 94

Lots of creative sleuthing that's happened around here.

I forgot about the extenders, which of course had to be assembler. Crazy!

The Robman · Posted: Wed Mar 01, 2023 2:27 pm Post subject:

The sleuthing usually comes into play when we see a set of learns that obviously have a checksum included in them, as we have to reverse engineer how it's calculated. The idea being that, when we write an executor to replicate the signals, we usually want the executor to calculate the checksum (unless it takes too much code). Also, we need to know how to generate the checksum if we want to try unused OBCs to search for secret discrete codes, etc.

Most checksums are easy, typically an XOR of each byte in the main signal, but some of them are a lot more complicated, like the 4DTV signal.
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Rob
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Please don't PM me with remote questions, post them in the forums so all the experts can help!