Whats that bitmask all about? Measurement_lv_mil_on

Cloudforce · **Joined:** Wed Aug 27, 2014 7:57 am **Posts:** 259

hello guys,

maybe someone smarter then me can chime in an give me a hint on this.

I´m trying to find the measurement value about the activation on the malfunction indicator lamp (mil). From the a2l i know its used at 0xFD1D.

Nevertheless there are 2 other measurement values that are connected to 0xFD1D.

Code:

/begin MEASUREMENT lv_mil_on
         "lv_mil_on"
         UBYTE
         RANGE________ON___1H__1H____OFF_
         2 2
         0 255
         ECU_ADDRESS 0xFD1D
         BIT_MASK 0x10
      /end MEASUREMENT

Code:

/begin MEASUREMENT lv_req_heat
         "lv_req_heat"
         UBYTE
         RANGE________0___0H__0H____1_819
         2 2
         0 255
         ECU_ADDRESS 0xFD1D
         BIT_MASK 0x80
      /end MEASUREMENT

Code:

/begin MEASUREMENT lv_var_sap
         "lv_var_sap"
         UBYTE
         RANGE________0___0H__0H____1_824
         2 2
         0 255
         ECU_ADDRESS 0xFD1D
         BIT_MASK 0x4
      /end MEASUREMENT

How do i deal with it in IDA?

dschultz · **Posted:** Wed Nov 18, 2015 10:09 am

viewtopic.php?t=10625

Cloudforce · **Joined:** Wed Aug 27, 2014 7:57 am **Posts:** 259

Thanks, found it after doing a google search on "BMW bitmask" :shock:

So i´ll try to understand the following. As 0xFD1D can´t be found in the disassembly, i´d choose 0xFD1A which is used two times:

Code:

/begin MEASUREMENT lv_aj_act
         "lv_aj_act"
         UBYTE
         RANGE________0___0H__0H____1_824
         2 2
         0 255
         ECU_ADDRESS 0xFD1A
         BIT_MASK 0x4
      /end MEASUREMENT
      /begin MEASUREMENT lv_aj_iga_cr
         "lv_aj_iga_cr"
         UBYTE
         RANGE________0___0H__0H____1_824
         2 2
         0 255
         ECU_ADDRESS 0xFD1A
         BIT_MASK 0x8
      /end MEASUREMENT

In the code, FD1A.* gets used many times. Unfortunally, there are FD1A.0 to FD1A.15 used in the code. So i tend to think its using 16 bits. I don´t think its as easy to say FD1A.4 is lv_aj_act and FD1A.8 is lv_aj_iga_cr? Nevertheless, why are there 16 different bit used?

mrf582 · **Posted:** Wed Nov 18, 2015 3:05 pm

FDXX.0 = 0 means bit 0 = 0
FDXX.1 = 1 means bit 1 = 1

bit 0 = 0
bit 1 = 2
bit 3 = 4
bit 4 = 8

and so on...

RomRaider

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Whats that bitmask all about? Measurement_lv_mil_on

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