How to recover from I2C bus collision BCLIF?

Question

I posted this a couple of days ago on the Microchip Forum (here) but the only response has been crickets. The I2C code below works most of the time but occasionally on power-up there is a bus collision (BCLIF) and the I2C module is unable to recover after the BCLIF. The I2C lines are pulled up by 3.3K ohms. Using REALICE and breakpoints I can see that i2c_write() resets BCLIF and returns FALSE when BCLIF is set. I have used a scope to verify that the I2C bus has flat-lined. Re-initializing the PIC18F25K20 I2C module (see init_i2c() below) when i2c_write() returns FALSE does not help. The PIC18F25K20 I2C is connected to a single slave device (MCP4018 I2C Digital POT). I have used this same code on previous PIC18 projects without issue so I replaced the MCP4018 suspecting a bad part but see no difference. Is there a way to reset the PIC18F25K20 I2C module when it is locked up?

void init_i2c(I2C_BAUD_RATE baud_rate, float freq_mhz) 
{ 
    UINT32 freq_cycle; 
    /* Reset i2c */ 
    SSPCON1 = 0; 
    SSPCON2 = 0; 
    PIR2bits.BCLIF = 0; 
    /* Set baud rate */ 
    /* SSPADD = ((Fosc/4) / Fscl) - 1 */ 
    freq_cycle = (UINT32) ((freq_mhz * 1e6) / 4.0); 
    if (baud_rate == I2C_1_MHZ) 
    { 
        SSPADD = (UINT8) ((freq_cycle / 1000000L) - 1); 
        SSPSTATbits.SMP = 1;        /* disable slew rate for 1MHz operation */ 
    } 
    else if (baud_rate == I2C_400_KHZ) 
    { 
        SSPADD = (UINT8) ((freq_cycle / 400000L) - 1); 
        SSPSTATbits.SMP = 0;        /* enable slew rate for 400kHz operation */ 
    } 
    else /* default to 100 kHz case */ 
    { 
        SSPADD = (UINT8) ((freq_cycle / 100000L) - 1); 
        SSPSTATbits.SMP = 1;        /* disable slew rate for 1MHz operation */ 
    } 
    /* Set to Master Mode */ 
    SSPCON1bits.SSPM3 = 1; 
    SSPCON1bits.SSPM2 = 0; 
    SSPCON1bits.SSPM1 = 0; 
    SSPCON1bits.SSPM0 = 0; 
    /* Enable i2c */ 
    SSPCON1bits.SSPEN = 1; 
} 
BOOL i2c_write(UINT8 addr, const void *reg, UINT16 reg_size, const void *data, UINT16 data_size) 
{ 
    UINT16 i; 
    const UINT8  *data_ptr, *reg_ptr; 

    /* convert void ptr to UINT8 ptr */ 
    reg_ptr  = (const UINT8 *) reg; 
    data_ptr = (const UINT8 *) data; 
    /* check to make sure i2c bus is idle */ 
    while ( ( SSPCON2 & 0x1F ) | ( SSPSTATbits.R_W ) ) 
        ; 
    /* initiate Start condition and wait until it's done */ 
    SSPCON2bits.SEN = 1; 
    while (SSPCON2bits.SEN) 
        ; 
    /* check for bus collision */ 
    if (PIR2bits.BCLIF) 
    { 
        PIR2bits.BCLIF = 0; 
        return(FALSE); 
    } 
    /* format address with write bit (clear last bit to indicate write) */ 
    addr <<= 1; 
    addr &= 0xFE; 
    /* send out address */ 
    if (!write_byte(addr)) 
        return(FALSE); 
    /* send out register/cmd bytes */ 
    for (i = 0; i < reg_size; i++) 
    { 
        if (!write_byte(reg_ptr)) 
            return(FALSE); 
    } 
    /* send out data bytes */ 
    for (i = 0; i < data_size; i++) 
    { 
        if (!write_byte(data_ptr)) 
            return(FALSE); 
    } 
    /* initiate Stop condition and wait until it's done */ 
    SSPCON2bits.PEN = 1; 
    while(SSPCON2bits.PEN) 
        ; 
    /* check for bus collision */ 
    if (PIR2bits.BCLIF) 
    { 
        PIR2bits.BCLIF = 0; 
        return(FALSE); 
    } 
    return(TRUE); 
} 
BOOL write_byte(UINT8 byte) 
{ 
    /* send out byte */ 
    SSPBUF = byte; 
    if (SSPCON1bits.WCOL)       /* check for collision */ 
    { 
        return(FALSE); 
    } 
    else 
    { 
        while(SSPSTATbits.BF)   /* wait for byte to be shifted out */ 
            ; 
    } 
    /* check to make sure i2c bus is idle before continuing */ 
    while ( ( SSPCON2 & 0x1F ) | ( SSPSTATbits.R_W ) ) 
        ; 
    /* check to make sure received ACK */ 
    if (SSPCON2bits.ACKSTAT) 
        return(FALSE); 
    return(TRUE); 
}

I can't see the code where SDA and SCL pins are configured as inputs. — Andrejs Cainikovs, Sep 21 '11 at 19:28
Can you try exchanging start condition initiating and first check for bus collision in i2c_write() and execute this function few times in a row with some small delays in between when this problem occurs? What happens then? — Andrejs Cainikovs, Sep 21 '11 at 20:00
Also, it could be really handy if you have oscilloscope with auto-trigger, so you can monitor what is the behavior of SDA line after power-up. Datasheet states: *If at the beginning of the Start condition, the SDA and SCL pins are already sampled low, or if during the Start condition, the SCL line is sampled low before the SDA line is driven low, a bus collision occurs, the Bus Collision Interrupt Flag, BCLIF, is set, the Start condition is aborted and the I2C module is reset into its Idle state*. — Andrejs Cainikovs, Sep 21 '11 at 20:04
@AndrejsCainikovs: SDA and SCL pins are configured as inputs elsewhere or the I2C wouldn't work at all. — jacknad, Sep 21 '11 at 21:05
Looks like this also applies to the dsPICs as well, since I'm seeing the same thing. — Seidleroni, Dec 05 '13 at 15:16

score 10 · Accepted Answer · edited Jun 20 '20 at 09:12

This Errata needs to be added to PIC18F25K20 Errata.

PIC18F2455/2550/4455/4550 Rev. A3 Silicon Errata

17 Module: MSSP

It has been observed that following a Power-on Reset, I2C mode may not initialize properly by just configuring the SCL and SDA pins as either inputs or outputs. This has only been seen in a few unique system environments.

A test of a statistically significant sample of preproduction systems, across the voltage and current range of the application's power supply, should indicate if a system is susceptible to this issue.

Work around

Before configuring the module for I2C operation:

Configure the SCL and SDA pins as outputs by clearing their corresponding TRIS bits.

Force SCL and SDA low by clearing the corresponding LAT bits.

While keeping the LAT bits clear, configure SCL and SDA as inputs by setting their TRIS bits.

Once this is done, use the SSPCON1 and SSPCON2 registers to configure the proper I2C mode as before.

@AndrejsCainikovs: Yes. It worked. Can't accept this answer till tomorrow. — jacknad, Sep 22 '11 at 12:40

score 2 · Answer 2 · answered Sep 27 '11 at 23:08

2

This same bug seems to ocur on PIC18F26K20/SS (Revision B3) too, also needs to be added to it's errata.

answered Sep 27 '11 at 23:08

Bruno

543
2
7
21

score 2 · Answer 3 · answered Nov 14 '11 at 19:46

I don't know your specifics but I ran into a problem once where the microcontroller was coming out of reset way early (much before Vdd stabilized on the I2C bus). So the uController started to read / write data before the target could function properly causing all sort of I2C operational issues.

score 1 · Answer 4 · answered Jun 07 '19 at 21:33

This errata also helped me with I2C stuck on PIC18F27J53 (but in my case there was also needed unlock of I2C bus blocked by SGP30 device, code example here: https://github.com/esp8266/Arduino/issues/1025#issuecomment-158667929) I finally decided to implement routine performing restart-unstuck-restart called when start condition fails (code fragment of my I2C stack):

eI2Cerr i2c_do_RUR(void) {
    //performs restart-unstuck-restart
    eI2Cerr   eRetVal;

    eRetVal = i2c_do_restart();
    if (eRetVal == I2C_ERR_TIMEOUT_RSEN_COLLISION) {
        i2c_unstuck(true); //true=performs also I2C bus unlock
        eRetVal = i2c_do_restart();
    }
    return(eRetVal);
}

I2C seems to be stable and working well now.

How to recover from I2C bus collision BCLIF?

4 Answers4