i2c message max buffer size

[Varouzan]

Hello,

I am using the nrf9160DK and I am implementing on zephyr.

For my application I need to write to an external flash memory through I2C. I need to write one page at a time + CRC bytes. In total I need to write 8210 bytes.

However using a logic analyzer I noticed that when I tried to send 8210 bytes, the 9160 actually wrote 18 bytes. When I tried to write 8192 bytes the 9160 wrote 0 bytes and when I tried to write 8191 bytes the 9160 wrote 8191 bytes. So it looks like uart message length "overflows" at 8k bytes.

My question is:

Is there a built in max length for i2c transactions? is that 8k bytes? Is there a way around that? 

[Øyvind]

Hello, 

Is there a built in max length for i2c transactions? is that 8k bytes? Is there a way around that? 

The transmit buffer of the nRF9160 has a maximum value of 0x1FFF or 8191 bytes. Please see TWI Master Write Sequence for more information

[Varouzan]

So to work around that, I would have to use EasyDMA? Are there any examples of that or how to use EasyDMA or TWIM instead of "traditional" I2C using zephyr ?

[Øyvind]

The only I2C sample we have at the moment is the BH1749: Ambient Light Sensor IC used on the Thingy:91. 

Is there a reason why you can't divide your write process into smaller chunks i.e. one page at a time with a stop condition after each page?

[Varouzan]

Yes. I have to write the page+ checksum bytes at one transaction, so 8210 bytes at one go.

What functions am I supposed to use to utilize twim.  those at zephyr\ext\hal\nordic\nrfx\drivers\include nrfx_twim.h? those at zephyr\drivers\i2c  i2c_nrfx_twim.c (can't find .h header for those)?

Looking into nrf9160.h and  NRF_TWIM_Type and its  member TWIM_TXD_Type 

typedef struct {
  __IOM uint32_t  PTR;                          /*!< (@ 0x00000000) Data pointer                                               */
  __IOM uint32_t  MAXCNT;                       /*!< (@ 0x00000004) Maximum number of bytes in transmit buffer                 */
  __IM  uint32_t  AMOUNT;                       /*!< (@ 0x00000008) Number of bytes transferred in the last transaction        */
  __IOM uint32_t  LIST;                         /*!< (@ 0x0000000C) EasyDMA list type                                          */
} TWIM_TXD_Type;                         

it looks like  MAXCNT refers to TXD.MAXCNT?

So even with TWIM is it possible to send more that 8191 bytes? yes or no?

[Øyvind]

Can you please provide the name of the device you are trying to interface? Or a datasheet? How are you using the I2C? You should use commands found in: zephyr\include\drivers\i2c.h

Kind regards,
Øyvind

[Varouzan]

The device I am trying to interface with is max32664C. I am trying to flash the application firmware for it.

I am using zephyr\include\drivers\i2c.h.

[Øyvind]

From what I see you will need to divide the data into chunks of let's say 1000 bytes. You will then need to write each chunk without a stop condition (opposite of what I first wrote), then on the last chunk, you write stop condition.

Kind regards,
Øyvind

[Balamurugan]

Hi,

We are trying to interface nRF52832 with  max32664C using i2c. While writing 8210 bytes, only 18 byes succeeds.

Facing same issue.

Have you resolved the issue and what is the solution?

[Gaurav Dubey]

I am trying to write the .msbl file to max32664c interfaced with nrf52840 and having the same issue.

I am unable to write 8210 bytes in one go and in chunks it throughs an error.

Have anyone resolved this issue.

[Gaurav Dubey]

Gaurav Dubey said:

I am trying to write the .msbl file to max32664c interfaced with nrf52840 and having the same issue.

I am unable to write 8210 bytes in one go and in chunks it throughs an error.

Have anyone resolved this issue

[Øyvind]

Gaurav Dubey, please open a new ticket with your issue. Please add what version of NCS you are using and what issues you are seeing.

Thanks! 

Kind regards,
Øyvind