Posted by planetbeing on under wine fest, spring beer, iphe, pain in the butt, th step, funny name, pmu, hande, framerate, sime, management unit, chip sets, lcd panel, framebuffer, power management, init, two steps, award winner, general purpose, many things | 
Looks like the LCD initialization stuff wasn't as simple as I thought. Depending on the way you look at it, there are three or four major initialization steps for the display. The first step initializes the display controller chip, sets the clock and everything. The could of messages you see about the framerate and clock are from this step. The second step ought to initialize the framebuffer for the display controller. I've reverse engineered and implemented those two steps so far.
The third step is to communicate with the LCD panel itself, and likely configure it and configure the display controller for it as well. This is the infamous "merlot_init" function. I have no idea what merlot is (other than a wine variety). Could be the codename for the driver, or the display controller. Can't be for the LCD itself, since its design to hande many different panel types. It's a pretty funny name, though, so I've started working on syrah_init. Syrah, because the 2005
Dalla Vina vintage was an award-winner at the Spring Beer & Wine Fest that I went to last year.
The problem with merlot_init is that it uses GPIO, SPI, IĀ?C as well as memory mapped registers to communicate with the panel and/or the display controller. That's almost every single bus on the iPhone, so basically I had to write drivers for those controllers as well before I could start on merlot_init. Those are now written; no idea if they work, but they're written. It's going to be a big pain in the butt to debug such a complicated driver. There's just too many things that can go wrong.
It's possible I might start implementing some of the PCF50633 (iPhone's power management unit) functionality. I can at least access powernvram (the general purpose memory registers on the PMU, really) pretty simply using IĀ?C and I ought to be able to test that piece out anyway.
On another note, for the longest time I couldn't figure out what those gpmem registers did on the PMU. I reversed some code that manipulated them, but I couldn't figure out where the data was being used, etc. However, I didn't spend much time on it because I didn't think they were going to be very important for what I was doing (since their values don't affect the initialization of any of the other drivers). Well, last night I told MuscleNerd about this for some reason, and he pointed out that there's a command called "powernvram" in iBoot that, no less, attaches descriptions to every single one of those registers! They just keep track of boot failures and stupid stuff like that. It just goes to show that you can't spend TOO much time just doing static RCE. Sometimes you've got to fire up the actual application, or at least give the old ztringz a go. ;)
Tagi: wine fest, spring beer, iphe, pain in the butt, th step, funny name, pmu, hande, framerate, sime, management unit, chip sets, lcd panel, framebuffer, power management, init, two steps, award winner, general purpose, many things
Posted by planetbeing on under gamma table, th project, menu interface, byte values, iboot, lcd panel, two bits, kilobytes, svn, spi, init, linux |
After many frustrating hours debugging all the pieces that fit into this LCD driver, it now behaves as expected. Unfortunately, I still can't get the gamma table to install from a clean start-up (where openiboot powers down everything that iboot powers down before starting them back up). I think this is probably because the gamma table installation code that I reversed from iBoot is only designed to work in situations where the code is directly loaded from LLB. The other possibility is that I made a mistake somewhere in merlot_init. I know that the rest of my code is good because it generates the exact same register configuration that iBoot does. merlot_init is more difficult to diagnose because of all the SPI commands flying around. Most of them just read and write to registers on the LCD panel, though.
What's interesting about the gamma table installation function in iBoot is that it uses a custom, rudimentary form of compression. The gamma table is just a mapping from every R, G and B value (0 - 0xFF) to a range from 0 - 0x3FF. There are three table, one for red, one for green and one for blue. Each table has 0x100 4-byte values. That adds up to 3 kilobytes worth of tables! Since space on the NOR is at a premium, it's sensible that Apple use some kind of fast compression to store the gamma table data. Their compression encodes values two bits at a time, and takes advantage of the fact that each entry in the gamma table will be fairly close to the value of the last entry, just offset a little. They use the two bit control codes to select how to manipulate the differences. Iā??m not sure if this is any sort of standard compression, but I thought it was amusing that they had this in here. You can look in the
iPhone Linux SVN for the code.
Still, we have working code and just a relatively minor problem! I think that means we could probably start some sort of
logo contest. Here's how I think it will work: We need art for the bootloader menu interface. The art will naturally have to feature iPhone Linux, so that means that we also require a logo for this project. So we need the following things: A logo for iPhone Linux, and a logo (could be just a variant of the iPhone Linux logo) for openiboot (not sure what the canonical capitalization of that should be; we will probably use the logo as the reference). We also need art for the bootloader based on those logos. What I'm envisioning is just the logos, bracketed by arrows to make it obvious that you can select between them. Then, the standby key can be used to toggle through the various choices, and the home key will boot the selected one.
The winning set of artwork will be selected by
community consensus. The community is very small as of yet, so I'm sure it'll be easy to just to talk it over with everyone and decide what people like.
It's important to note that even if your logo is chosen, if someone offers us something prettier, we will switch, so don't do this if your feelings are easily hurt. =P
I really appreciate what artists do and the care and craftsmanship that they put into their work. You guys have a skill that I will never have and I know that it is a lot to ask to have you put that kind of work into something that might not even be used. However, I and many others have put analogous care into crafting the code for this project, and that is our salute to the community. So let's make something beautiful together.
To submit an entry, just contact me or cmw with it in some way, shape or form. Either on my gmail account (take a wild guess what my gmail address is :P), or on IRC, or here in the comments, or whatever. We'll see to it that everyone gets a chance to take a look at it.
Tagi: gamma table, th project, menu interface, byte values, iboot, lcd panel, two bits, kilobytes, svn, spi, init, linux
