Need help with UART on MPC5748

[shijiaguo]

I'm trying to test out the UART periphral on MPC5748G, but I’m stuck at where I’m trying to write data into the BDRL data buffer, while the UART is configured as FIFO mode.

Here are my initialization code:

void UART_init()

{

    LINFlexD_0.LINCR1.B.SLEEP = 0;  /* Clear Sleep bit */

    LINFlexD_0.LINCR1.B.INIT = 1;   /* Enter INIT mode */

    LINFlexD_0.UARTCR.B.UART = 1;   /* Enable UART mode */

    LINFlexD_0.UARTCR.B.RFBM = 1;   /* Rx FIFO mode */

    LINFlexD_0.UARTCR.B.TFBM = 1;   /* Tx FIFO mode */

LINFlexD_0.LINCR1.B.INIT = 0;   /* Leave INIT mode */

}

Here’s the write function:

void UART_tranceive(void)

{

    LINFlexD_0.UARTCR.B.TxEn = 1;

LINFlexD_0.BDRL.B.DATA0 = (uint8_t)0x08;

}

Every time this is run: LINFlexD_0.BDRL.B.DATA0 = (uint8_t)0x08, there’s the critical exception generated.

Can anyone tell me if I’m doing something wrong?

Also does anyone happen to have some sample code of UART? If it’s with DMA that would be even better. Thank you so much!

-Shijia

[lukaszadrapa · Accepted solution]

Hi,

this is the problem (copied from RM):

You need to force the compiler to use "stb" instruction (store byte).

If you use this one:

LINFlexD_0.BDRL.B.DATA0 = (uint8_t)0x08;... it reads 32bit word, mask the data and then write 32bit word back. But this is not allowed. As you can see in the table above, only "store byte" or "store half-word" instruction is allowed. Read operation is not allowed too. So, you can use something like this:

*(unsigned char*)(((unsigned int)(&LINFlexD_0.BDRL.R))+3) = ...;

Take the address of BDRL register, add 3 to get address of the byte 0 and re-type the address to pointer to byte. Then the compiler will use stb instruction and it will work.

In this SW example you can find functions for UART (without FIFO):

Example MPC5748G PinToggleStationery GHS614

Regards,

Lukas

[shijiaguo]

Hi Lukas lukaszadrapa​

Thank you so much, it totally makes sense. I had a suspicion too, but didn't know how to address it.

One more quick question, once I configure it as FIFO mode, I'm no longer able to see the BDRL and BDRM register values on my debugger. Is that normal? It shows up like this:

-Shijia

[shijiaguo]

I guess ignore my first question, I think it's my debugger trying to read all bytes at the same time and there might be some bus error. 

[lukaszadrapa]

Hi,

I did quick test on my board and it works. See attached example. I used LINFlex 2 to be able to use USB-to-serial interface.

By the way, you can't see the BDRL and BDRM registers in debugger for the same reason which I mentioned in my first post - read of BDRL in FIFO mode is not allowed ever,  in case of BDRM we can read only byte 4 or half-word 2. Debugger probably uses word access, so it results in bus error.

Regards,

Lukas

[shijiaguo]

Thank you so much lukaszadrapa‌. It's working. What I missed was I was probing on the wrong pin and didn't connect the pad.... 

[shijiaguo]

Also I'm kinda stuck again after I did some more development. 

So here's my code:

void peri_clock_gating (void)
{
/*
* IMPORTANT: This function is called before the RAM initialization for
* sections .data and .bss is done so it must NOT rely on any initial
* value of a global or local static variable.
*/
MC_ME.RUN_PC[0].R = 0x00000000; /* gate off clock for all RUN modes */
MC_ME.RUN_PC[1].R = 0x000000FE; /* config. peri clock for all RUN modes */
MC_ME.PCTL[50].B.RUN_CFG = 0x1; /* LIN_0: select peri. cfg. RUN_PC[1] */
}

[shijiaguo]

Sorry to be continued. 

void UART_init()
{
LINFlexD_0.LINCR1.B.INIT = 1; /* Enter Initialization Mode */
LINFlexD_0.LINCR1.B.SLEEP = 0; /* Exit Sleep Mode */
LINFlexD_0.UARTCR.B.UART = 1; /* UART Enable- Req'd before UART config.*/
LINFlexD_0.UARTCR.R = 0x0033; /* UART Ena, 1 byte tx, no parity, 8 data*/
LINFlexD_0.UARTSR.B.SZF = 1; /* CHANGE THIS LINE Clear the Zero status bit */
LINFlexD_0.UARTSR.B.DRFRFE = 1; /* CHANGE THIS LINE Clear DRFRFE flag - W1C */

LINFlexD_0.LINCR1.B.INIT = 0; /* Exit Initialization Mode */

SIUL2.MSCR[245].B.SSS = 1; /* Pad PP5: Source signal is LIN0_TX */
SIUL2.MSCR[245].B.OBE = 1; /* Pad PP5: OBE=1. */
SIUL2.MSCR[245].B.SRC = 3; /* Pad PP5: Full strength slew rate */

}

void UART_tranceive(void)
{
/while (LINFlexD_0.UARTSR.B.DTFTFF == 0) {;} /* Wait for data trans complete*/
LINFlexD_0.UARTSR.R &= 0x02; /* Clear DTFTFF flag - W1C */

LINFlexD_0.BDRL.B.DATA0 = 0x08;

}

[shijiaguo]

Sorry I don't know why everytime I hit ctrl-s it just post it...

Continue...

My UART_tranceive() is called periodically (every 1 ms). So here since I connected LIN0_Tx with Pad PP5, I should see UART Tx signals on PP5, right? However, I'm not seeing anything on PP5. I can see that the UARTSR_DTFTFF is toggling between 0 and 1. I'm using MPC5748G EVB board: http://www.nxp.com/files/microcontrollers/doc/user_guide/MPC5748GEVBUG.pdf?fasp=1&WT_TYPE=Users%20Gu... 

Am I missing something? Any help is appreciated. Thank you!

lukaszadrapa‌  

[alexvinchev]

Hi shijiaguo

You might find helpful this thread:

https://community.nxp.com/message/628324?commentID=628324#comment-628324