CSL '0401' Program Binary Disassembly Notes

[terra]

Cool. I guess 'Address access time = (2.5 + WS) t_cyc – t_CHAV – t_DICL' is probably the relevant formula? Though t_CHAV has a rather large range in the datasheet so I'm not sure what to enter as a calculation. Seems like BMW is selecting flash memory that should allow for 0 wait states in most scenarios.

If I assume the target access time would be proportional to the clock speed difference, ~76ns should be acceptable (assuming 20.97MHz for MSS52/4 and 24.76 MHz for MSS54HP which I believe is correct) -- so either way I think you're right in the 70ns likely being acceptable (there are also some ancient 29f400ab's occasionally available that came in 75ns, those may work too)

[karter16]

I think this is the right diagram (from page 283 onwards here: https://github.com/karter16/CSL_0401.../MC68376.pdf):



The whole read cycle is approximately 4 clock cycles, but the data needs to be stable on the bus by the time DSACK is low for sampling. I didn't go through the table and work it out but it looks to me to be somewhere in the region of 1.25 to 1.75 clock cycles between the address being stable and data needing to be read (So as you say, less than 2 clock cycles).

I would imagine from this that 70ns is probably just fast enough to work, but I don't know whether it's too close to the edge (pun intended) or not. I'd think 90ns would likely be less successful given that's definitely more than 2 clock cycles.

[terra]

Karter - since you seem to have a decent handle on the DME's timing, was wondering if you had any thoughts on how critical the flash memory's rated access time is. Every factory MSS54HP I've seen had the 55ns parts. But I've also seen people use the 70ns parts without apparent issue. MSS52/4 seem to have come with 70ns and 90ns from what I've seen.

If I did the math right, a single cycle on an MSS54HP (25MHz) would take 40ns and on an MSS52/4 (20MHz) would be 50ns -- so seems like they're targetting an access time that's less than what two cycles would take? If upto 80ms is acceptable, makes sourcing flash memory for HP conversions a little easier

(though old MSS52s seem to have a slightly older revision of the CPU, which does make me wonder if those would be suitable for the MSS54HP code at all)

[terra]

Was working through some unknown variables in the DPR that needed figuring out and came across this:



This is where the CVNs are generated for CARB. They're built off the CRCs of the various sections same as is done elsewhere, but here they're XOR'd with various values - I'm gunna go ahead and guess that that was to stop it being used as a way to generate checksums (unless anyone has any other ideas) the CARB specification makes no mention of anything that would explain it.

I guess it makes it harder to generate an arbitrary checksum if you don't know the algorithm, but if one makes the connection that generating a checksum to match the original results in the CVN also matching the original, then it's kinda moot. They probably just thought they were being cute with the MS_S stuff.

CARB does leave it entirely to the manufacturer on how to calculate it. On various non-M DMEs from the E6x/9x generation (MS45, MSx70/8x), the CVN is simply the same as the stored checksum (CRC32 in those cases). I'm not sure about MSS6x, I never looked into that.

[karter16]

4D 53 5F 53 35 34 35 32 in ASCII reads MS_S5452

Ha nice! I'd missed that


Sent from my iPhone using Tapatalk

[bmwfnatic]

4D 53 5F 53 35 34 35 32 in ASCII reads MS_S5452

[karter16]

Was working through some unknown variables in the DPR that needed figuring out and came across this:



This is where the CVNs are generated for CARB. They're built off the CRCs of the various sections same as is done elsewhere, but here they're XOR'd with various values - I'm gunna go ahead and guess that that was to stop it being used as a way to generate checksums (unless anyone has any other ideas) the CARB specification makes no mention of anything that would explain it.

[karter16]

These are the P_UMG (ambient pressure) functions.

p_umg_init() runs once in the initialisation function when the DME boots. It establishes the starting values for the key variables.




p_umg_get() runs in the 100ms task, it acquires the latest value from the ambient pressure sensor via the AD channel, performs error checking (via p_umg_diag()), builds a variable to send p_umg over CAN, etc.




p_umg_hoehe_ber() runs in the background task and calculates the current estimated height above sea level based on current ambient pressure.




p_umg_diag() is called by p_umg_get(). It establishes plausibility of the ambient pressure sensor reading, updates P_UMG_FILTER with either the valid reading, an ersatz (replacement) value, etc. This function is interesting as the 0401 version contains a bunch of additional logic. In the event that when the DME starts it is unable to acquire a plausible reading from the ambient sensor it will use, if it is error free, the MAP pressure as an ersatz (replacement) value for P_UMG. The reason it can do this is that on first start up, before the engine is running, the manifold pressure is the same as ambient. This means that while the engine is running the ersatz value isn't able to be updated, but under a lot of conditions it will still be more accurate than just falling back to K_P_UMG_ERSATZ (955mbar).




Edit: If you're wondering there is some method to my madness. I'm, looking at the air mass functions and wanted to be 100% sure about how p_umg was/wasn't used, hence the side quest into the p_umg functions.

[bmwfnatic]

Yeah, there's clearly more out there than is publicly available. Though I would argue the MSS5x are understood well enough for there already to be no point in hoarding files - most tuners are doing little more than editing the main ignition and fueling tables.

I do wonder if BMW gives some definitions on the motorsport side of things since I imagine those cars are recalibrated pretty often. Though I don't know if I've ever seen an MSS54 in the motorsports parts listing (MSS60 yes though)

It mentions ECU 406 and ECU 400 and a separate VANOS ECU in the P54B32 catalog, nothing explicitly about the MSS indeed.

[terra]

This will 100% happen one day, we know it's out there, and people love to gate keep until there's no point anymore.

Yeah, there's clearly more out there than is publicly available. Though I would argue the MSS5x are understood well enough for there already to be no point in hoarding files - most tuners are doing little more than editing the main ignition and fueling tables.

I do wonder if BMW gives some definitions on the motorsport side of things since I imagine those cars are recalibrated pretty often. Though I don't know if I've ever seen an MSS54 in the motorsports parts listing (MSS60 yes though)

[bmwfnatic]

I have this horrible nagging feeling that one day I'm going to declare my efforts "complete" and the next day someone will be like "oh btw, here's the source code for the CSL" lol. There's definitely a couple of people out there who have more CSL-specific info.

This will 100% happen one day, we know it's out there, and people love to gate keep until there's no point anymore.

[karter16]

Sure would be nice if we could get access to some MSS54 ELFs

I have this horrible nagging feeling that one day I'm going to declare my efforts "complete" and the next day someone will be like "oh btw, here's the source code for the CSL" lol. There's definitely a couple of people out there who have more CSL-specific info.

[terra]

Yeah hard to say for sure. I also have a suspicion that the some of the CSL stuff was borrowed from the MSS6x project given the development timelines, but the two projects very well could have had different naming conventions. Though a lot of names are shared, so it might just be their convention is a little more fluid and it more came down to whichever engineer started writing the code.

As far as m vs mzyl -- I think they probably would have noted that the value is a per cylinder calculation in the naming scheme, though perhaps m_zyl would have been the convention on the MSS5x

Sure would be nice if we could get access to some MSS54 ELFs

[karter16]

Here's mzyl_berech(). This is what I'd previously identified as m_calc(). I'm not 100% sure that the function/parameter/variable names that I've pulled through from MSS65 are what BMW ACTUALLY used in the MSS54 code. I think it's more likely that PSAU is p_saug for example, in line with the way other pressure and temp variables were named in the MSS54. I think too that MZYL was possibly just M, etc. but I'm definitely going to opt for known actual names over made up names, so have pulled through the MSS65 naming where there wasn't already a 100% known name from MSS54. ? at the end of a variable name represent where I don't have a definitive name, not necessarily that I have any uncertainty about what it is/does.

[karter16]

Ahh this is so satisfying for my brain.

I've gone through rg_berech() (MSS65) and compared it to rg_m_calc() (my MSS54 disassembly) and the rg (rest-gas) calculation is effectively the same. I've been able to match everything up and identify the actual names for the maps and parameters. This confirms that my understanding of how it was working was pretty much on the money.

The only significant difference between the two (aside from MSS65's bank handling, and differences in base units) is that the MSS65 function includes a lookup to a table which gives a delta adjustment based on expected intake manifold pressure. This isn't included in the MSS54 function although I haven't yet figured out whether it's effectively accounted for elsewhere in the calculation path.

The other thing of note is that the MSS54 has an unused option to just lookup rg mass from a lookup (KF_RG_M) the equivalent lookup doesn't exist in the MSS65 code.


MSS54 rg_berech()