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LIN bus built-in function source code ?
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WalkOver



Joined: 14 May 2021
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LIN bus built-in function source code ?
PostPosted: Fri Dec 10, 2021 8:49 am     Reply with quote

Hello,

I'm working on LIN bus to control a LIN water pump (Pierburg CWA400) with a dsPIC33CK MCU and a MCP2021A driver.
I managed to send a command to start the pump, everything is good on scope and logic analyser...but it is working only after a power supply OFF/ON cycle.

If the +12V is already present on the LIN bus, the program hangs during linbus_header() function which is problematic for me.

Is the code for the built-in LIN functions are available somewhere ?
Or does anyone have any idea to work around the problem?

Thank you very much for your help Smile
dyeatman



Joined: 06 Sep 2003
Posts: 1910
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PostPosted: Fri Dec 10, 2021 9:41 am     Reply with quote

Version 5.095 added Linbus support and example code in the examples folder
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WalkOver



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PostPosted: Fri Dec 10, 2021 10:04 am     Reply with quote

Hello,

Thank you for your help but I actually forgot to specify my compiler version.
I have the last one ( 5.105 ) and I already check the included example.

I guess I'm doing everything right since it works with an automotive grade water pump...but only after a power supply OFF/ON cycle.

If the +12V is already present before the MCU init routine, the program hangs inside the linbus_header() function.
It hangs too if I manually disconnect the LIN bus from the pump.
I have to manually power OFF/ON my power supply and everything works fine again.
dyeatman



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PostPosted: Fri Dec 10, 2021 10:36 am     Reply with quote

Here is a good document showing the bus wiring. Since it shows the Linbus
pulled up to VS all the time I suspect something else is wrong

http://ww1.microchip.com/downloads/en/DeviceDoc/article_ac9_two-wire-lin-networking.pdf[[/url]
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Ttelmah



Joined: 11 Mar 2010
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PostPosted: Fri Dec 10, 2021 11:48 am     Reply with quote

Understand there are not any Linbus drivers. Linbus uses at the PIC, RS232.
However that places the same restrictions on the hardware as for normal
RS232. The RX line must be high when nothing is being sent, or the receive
code will be continuously receiving. Linbus itself is just an open collector
drive into a single wire at up to 20000bps. As with RS232, it is well worth
testing the voltage level on the RX pin is high before enabling any form of
reception (especially interrupt driven). Being open collector, there has to
be a pullup to 12v somewhere on the bus. The driver chip you are using
provides a pullup when used as a slave, but not when used as a master.
Does the pump have a pullup?. It's data sheet does not say that it does.
If the line is not being pulled up to 12v, the PIC code will hang as it will
be continuously seeing data. Their example wiring shows an external 1.2K
resistor being used.
jeremiah



Joined: 20 Jul 2010
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Re: LIN bus built-in function source code ?
PostPosted: Fri Dec 10, 2021 12:04 pm     Reply with quote

WalkOver wrote:

Is the code for the built-in LIN functions are available somewhere ?


Aside from the examples already mentioned, you can look at the generated LST files to see the assembly used for each of the functions. Not as good as C code for reviewing, but it's something.
WalkOver



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PostPosted: Fri Dec 10, 2021 1:59 pm     Reply with quote

Thank you everyone for your help Shocked

As specified in datasheet, I have an external 1K pull up resistor on the bus.
The MCU UART module is configured as Master.

I spotted a problem :



On top, you can see the first header break after a power supply OFF/ON cycle and the water pump respond to the command.

On the bottom, you can see the first header break after a MCU reset ( done with a PICKIT4 ). There is ( I think ) a problem with the header sync.

Instead of using the built-in functions, I write the PID in the UxP1 register (U3P1 for me ) but I have almost the same issue, now the program no longer crashes but there is the same weird header sync after a hardware reset.

When everything is working after a power supply OFF/ON cycle, if I manually disconnect the pump from the bus, I also have this header sync problem and reconnecting the pump doesn't change anything.
I have to power OFF/ON the power supply.

Do you have any idea what's going on?
gaugeguy



Joined: 05 Apr 2011
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PostPosted: Fri Dec 10, 2021 2:25 pm     Reply with quote

Are you trying to use AutoBaud? A master sends the sync for the slave to use. The baud rate of the master should never be changed but it looks like your's is trying to change the baud rate.
WalkOver



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PostPosted: Fri Dec 10, 2021 2:29 pm     Reply with quote

Done Cool

Don't know why, but I have to reset and set the U3MODE.UARTEN register bit to reset the uart module in my MCU init routine.

With this trick, the LIN bus is working like a charm even after a hardware reset or after disconnecting the pump from the bus.
WalkOver



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PostPosted: Fri Dec 10, 2021 2:31 pm     Reply with quote

gaugeguy wrote:
Are you trying to use AutoBaud? A master sends the sync for the slave to use. The baud rate of the master should never be changed but it looks like your's is trying to change the baud rate.


No the baudrate is fixed at 19200 bauds.
Ttelmah



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PostPosted: Fri Dec 10, 2021 11:04 pm     Reply with quote

Glad you have it working.
Would suggest you try using the NO INIT option on the #use RS232,
then at the start of the code, wait till the RX line is seen as high, then
init the RS232.
Think what is happening is the UART is seeing one or more glitches
on it's RX line at the start.

I notice the Linbus example does not have ERRORS in it's RS232 setup.
Put this in.
Generally with CCS, if you are using the hardware UART, you _must_ either
have ERRORS in the declaration, or you need to test the UART error
bits yourself and clear if necessary.
With ERRORS there the UART will still work if it gets a framing error or
an overrun error. Without this, if either happens the UART will stop receiving.

It is a bit of a 'naughty' in some of the CCS examples, that they omit this.
WalkOver



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PostPosted: Sun Dec 12, 2021 8:50 am     Reply with quote

Ttelmah wrote:
Glad you have it working.
Would suggest you try using the NO INIT option on the #use RS232,
then at the start of the code, wait till the RX line is seen as high, then
init the RS232.
Think what is happening is the UART is seeing one or more glitches
on it's RX line at the start.

I notice the Linbus example does not have ERRORS in it's RS232 setup.
Put this in.
Generally with CCS, if you are using the hardware UART, you _must_ either
have ERRORS in the declaration, or you need to test the UART error
bits yourself and clear if necessary.
With ERRORS there the UART will still work if it gets a framing error or
an overrun error. Without this, if either happens the UART will stop receiving.

It is a bit of a 'naughty' in some of the CCS examples, that they omit this.


Hello Ttelmah,

I haven't tried yet to init the uart module after the RX line is stabilized.
But I already test and clear the OERR and the FERR bit inside the while loop.

OERR cannot be cleared in software ( silicon errata ), but never get set even when my LIN bus doesn't work anymore.

I will make more test following your advice.
Ttelmah



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PostPosted: Sun Dec 12, 2021 12:16 pm     Reply with quote

If you use an interrupt driven RX handler, it should be impossible to ever
get an OERR. Normally you have to read the byte associated with the
error as part of the clearing process. On the DsPIC's these errors are
attached to the byte where they occur.
PCM programmer



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PostPosted: Sun Dec 12, 2021 4:50 pm     Reply with quote

You asked for the source for linbus_header().

I looked at the ASM code for CCS vs. 5.105. There are only 3 places where it waits. These are shown below.
Code:

// This code is at the start of the function:

00004:  BCF    RCSTA1.CREN1  // Disable receiver
00006:  BSF    TXSTA1.SENDB  // Send Sync Break on next transmission
00008:  CLRF   TXREG1
0000A:  BTFSC  TXSTA1.SENDB  // Wait until break transmission is completed
0000C:  GOTO   000A

00010:  MOVLW  55
00012:  MOVWF  TXREG1        // Send 0x55
00014:  BTFSS  PIR1.TX1IF    // Wait until 0x55 char is transmitted
00016:  GOTO   0014

// .... A lot of code (not shown) to calculate checksum.

// This code is at the end of the function:

00066:  MOVWF  LINBUS_CHECKSUM_1  // Save checksum
00068:  MOVWF  TXREG1             // Send checksum byte
0006A:  BTFSS  TXSTA1.TRMT        // Wait until it is transmitted
0006C:  GOTO   006A

00070:  BSF    RCSTA1.CREN1
00072:  MOVF   param,W
00074:  GOTO   00B8 (RETURN)
WalkOver



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PostPosted: Mon Dec 13, 2021 10:34 am     Reply with quote

I was a little too fast....

I'm able to send header break, header sync and PID with my own function or the built in linbus_header() function.

Everything seems to works, the pump wakes up and transmit data.

BUT, I can't read out the DATA.
With the built-in linbus_rx_response(), the program hangs.
I tried to read data with just fgetc() in the while loop and the program hangs too...

I tried with an interrupt driven RX handler ( #INT_RDA3 ) in my case,
But this time, the program hangs if I use the built-in linbus_header() function Evil or Very Mad
It hangs too if I use my own Lin_send() function and the built-in fgetc function the the handler.

The best I can get is to use my own Lin_send() function and read the register U3RXREG in the handler, but the result is the PID I send and nothing more. After reading one time, the buffer is empty and I can read the other 8 bytes.

Does someone have an idea ? I want to tear my hair out.

Thank you very much
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