Limitations and Known Issues

There are some HW limitations in MT7688AN and known issues in the platforms. Here we summarize these information for reference:

Hardware limitations

I2C

Two I2C operation modes are not supported:

  • Clock stretching
  • Repeated start

SPI

  • The max size of the I/O buffer of SPI is 16 bytes. If a data transmission larger than 16 bytes is issued, there will be an error reported.
  • Full-duplex mode is not supported. Only half-duplex mode is supported.

I2S

  • Mono (1 channel) is not supported.
  • The supported sampling rates and data width are up to 192kHz / 24-bit.

Known issues

Wi-Fi driver

  • AP mode is with better performance than Station mode. [Solved in firmware v0.9.4 and above]
  • LinkIt Smart 7688 cannot be in both AP and Station mode at the same time (i.e. not available as a wireless repeater). [Supported in firmware v0.9.4 and above]
  • Monitor mode is not supported.
  • In Station mode, WPA-enterprise and WPA2-enterprise authentication protocols are not supported. WEP is not supported by default in OpenWrt due to its insecurity and it can be cracked in seconds.

USB

  • USB 2.0 devices will be detected as USB 1.1 devices. [Solved in firmware v0.9.3 and above]

I2S

  • WAV recording with WM8960 is not supported yet. [Solved in firmware v0.9.3 and above]

SPI

  • [v0.9.3] the .frequency() API in MRAA is not functional. Please use the spi-config command to adjust the SPI working frequency. The following command sets the SPI working frequency to 7MHz:
           # spi-config -d /dev/spidev32766.1 -s 7000000 [Solved in firmware v0.9.4 and above]
  • For LinkIt Smart 7688, the MSB of a data transmission might be error. LinkIt Smart 7688 Duo does no have this issue. [Solved in firmware v0.9.3 and above]
  • [v0.9.3] 16-bit data type is not functional. It can only work with 8-bit data type.

GPIO

  • GPIO 0 is occupied by the I2S driver and cannot be used as GPIO function.

UPM sensor support