ProfessWRX wrote:Tazzi wrote:
1) P04 ECUs are a heap of shit in terms of how there DLC (VPW) is handled internally. Not only does the OS affect how stable the comms are (Even when running a kernel), but they do not apply a strong load on the bus line which can result in them dropping frames if the bus line is not loaded significantly during read/write at 4x speed. Pete and I discovered this after monitoring the VPW pulses, and adding a resistor between VPW line to ground (2.7-4.6k was ideal) to help the DLC clean up its signal.
This issue did affect when using GM MDI when performing a flash update, where the DLC dropped to 1x mode when it detected too many errors on the line (Which also affected the OBDX VT in the same manner), keep this comment in mind. The GM MDI also logged this, and continued flashing at 1x since its internal DLC dropped to 1x also.
If this is the issue, then shouldn't I splice in a resistor into my bench harness and check?
Yes, you could test this and see if it helps at all for you.
ProfessWRX wrote:Tazzi wrote:
2) Looking at your reads, it uploaded the kernel perfectly, and then read a bunch of chunks in a row without any dropouts. Then suddenly completely loss all communication here:
Code: Select all
[05:27:51:538] Reading from 49152 / 0xC000, length 4096 / 0x1000
[05:27:51:554] XPro: 20 01 00 DE
[05:27:51:565] TX: 6D 10 F0 35 01 10 00 00 C0 00
[05:27:52:576] Timeout.. no data present A
[05:27:52:585] No payload following read request.
[05:27:53:594] Timeout.. no data present A
[05:27:53:603] No payload following read request.
[05:27:54:613] Timeout.. no data present A
It then repeats sending the request several times without a single response back. This indicates to me that either the DLC has dropped back to 1x mode, or the kernel has dropped out.
Personally, I believe the DLC has dropped back to 1x mode which is why all communication has completely ceased.
Is this is the case, would the Dash not remain the same? When this happens the dash resets.
Ahhhhhhhhhhhhhhhh Interesting!
So... when the dash 'resets', this means it is coming out of programming mode and is starting back up.
This would signify to me either:
1) Something in the car starting talking at 1x and caused the whole car to go back to 1x mode, and all wake up (reset).
2) Tester present took too long to be sent, so car exited programming mode and item1 occurred.
ProfessWRX wrote:Tazzi wrote:
The alternative here is the kernel dropping out, but... I don't think thats the problem until testing the above theory.
With the behavior I see this makes sense to me, but I'm a lowly tester, not a dev.
If the kernel dropped out, this 'could' result in the ECU speaking back at 1x mode again which would wake up the rest of the car also. I still suspect it is the issue mentioned above that is the problem, since 1x works fine.
I can test this out on my bench setup, but will need to know which kernel is being used here?
