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fivdi / i2c-bus

I2C serial bus access with Node.js
MIT License
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32 byte limitation #23

Closed sgoll closed 8 years ago

sgoll commented 8 years ago

I need to send payloads with more than 32 bytes to a connected peripheral (using raspi-i2c). The peripheral speaks plain I2C, not SMBus.

Unfortunately, the I2C methods provided seem to be hardwired to use the SMBus functions, in particular they all seem to fall back to i2c_smbus_access in the end.

Is it somehow possible to use plain I2C without the 32 byte limitation? According to this post http://stackoverflow.com/a/25984891, the Linux kernel seems to be able to send longer I2C packets when not using SMBus.

What would be the easiest way of sending longer packets using i2c-bus (and raspi-i2c)?

fivdi commented 8 years ago

i2c-bus supports both plain I2C and SMBus. The following four methods are plain I2C methods and should support payloads with more than 32 bytes:

i2cRead i2cReadSync i2cWrite i2cWriteSync

The corresponding raspi-i2c methods are:

read readSync write writeSync

The four raspi-i2c methods have an optional register argument. If the register argument is not specified, the raspi-i2c methods will call the i2c-bus plain I2C methods. Unfortunately, the raspi-i2c methods explicitly limit the payload size to 32 bytes currently (see checkLength.)

I'd suggest trying with the four i2c-bus plain I2C methods to see if it works.

sgoll commented 8 years ago

@fivdi Thank you for the detailed explanation. Somehow I was under the impression that the exception was thrown in i2c-bus code when I tried using the plain I2C functions provided by raspi-i2c.

I opened a ticket at raspi-i2c to discuss the issue there: nebrius/raspi-i2c#9.