I2C not expected receive NACK/ACK issue

javiervallori — Mon, 14 Nov 2022 11:52:04 GMT

Hi,

I am working in a product that runs with a LPC11E68. I noticed that the device hung sporadically beacuse of a i2c communication. Debuging into, I found out that the i2c returns a STA value of 0x58:

This is a return STA value only available in receive mode. But my transmision was configured only to transmit frame. The I2CM_XFER_T *xfer was configured with:

 xfer.slaveAddr = I2C_SLAVE_MCP_ADDR;
xfer.options = 0;
xfer.status = 0;
xfer.txBuff = txBuffer;
txBuffer[0] = I2C_MCP_CONFIG_POINTER;
txBuffer[1] = I2C_MCP_CONFIGURATION_VALUE;
xfer.txSz = 2;
xfer.rxBuff = rxBuffer;
xfer.rxSz = 0;

That means, it should be imposible to be at that state. Puting a breakpoint in the LPCopen i2c handler, I noticed that the code pass into the following point of the :

 /* Rx handling */
case 0x58: /* Data Received and NACK sent */
case 0x50: /* Data Received and ACK sent */

*xfer->rxBuff++ = pI2C->DAT; //Breakpoint
xfer->rxSz--;

The firmware stops at that breakpoint when it hangs, but the xfer->txSz was still with 2 value. That means it hadn't started the transmision. And what's worse, entrying in that STA handler "imposible" value, because xfer->rxSz had a 0 value, the decrement pass xfer->rxSz to 65535 causing a big damage in the memory .

That code works without any IRQ. It is just a simple Chip_I2CM_XferBlocking() call. I fixed it just checking first a none 0 xfer->rxSz value before decrement.

 /* Rx handling */
case 0x58: /* Data Received and NACK sent */
case 0x50: /* Data Received and ACK sent */
if (xfer->rxSz) {
  *xfer->rxBuff++ = pI2C->DAT;
   xfer->rxSz--;
}

This code does not hinder, but the peripheral must not enter into this STA value without starting a receive transmition, and that is why this extra code should not be necessary. I consider the LPCopen code well written, and seems to be a hardware issue or something I missunderstand.

I am scratched with this behaviour, and I would like if somebody has had some similar experience.

Thank you

Re: I2C not expected receive NACK/ACK issue

Pavel_Hernandez — Tue, 15 Nov 2022 04:48:25 GMT

Hello,

Could you tell me what is the example you based on?

Best regards,
Pavel

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I2C not expected receive NACK/ACK issue

Re: I2C not expected receive NACK/ACK issue