SPRUIM2 User guide

SPRUIM2H May 2020 – October 2023 AM2431 , AM2432 , AM2434 , AM6411 , AM6412 , AM6421 , AM6422 , AM6441 , AM6442

12.1.3.4.7.3 I2C Draining Feature

Note:

DMA mode and SCCB Protocol are not supported on this family of devices.

The draining feature is implemented to handle the end of a transfer whose length is not a multiple of the FIFO threshold values (the I2C_BUF[13-8] RXTRSH bit field value + 1 for the RX threshold and the I2C_BUF[5-0] TXTRSH field value + 1 for the TX threshold). It can also transfer the remaining number of bytes (because the threshold is not reached).

This feature prevents the LH or the DMA controller from trying more FIFO accesses than necessary (for example, to generate at the end of a transfer a DMA RX request having fewer bytes in the FIFO than the configured DMA transfer length). Otherwise, an AERR interrupt is generated by the I2C_IRQSTATUS_RAW[7] AERR bit.

The draining mechanism generates an interrupt using the I2C_IRQSTATUS_RAW[13] RDR or I2C_IRQSTATUS_RAW[14] XDR bit at the end of the transfer, informing the LH that it must check the amount of data left to be transferred (the I2C_BUFSTAT[13-8] RXSTAT or I2C_BUFSTAT[5-0] TXSTAT bit fields) and enable the draining feature of the DMA controller by reconfiguring the DMA transfer length according to this value (when the DMA mode is enabled) or perform only the required number of data accesses (when the DMA mode is disabled).

In receive mode (controller or target), if the RX FIFO threshold (the I2C_BUF[13-8] RXTRSH bit field value + 1) is not reached, but the transfer ends on the I²C bus and data remains in the RX FIFO (less than the threshold), the receive draining interrupt (the I2C_IRQSTATUS_RAW[13] RDR bit) is asserted to inform the LH that it can read the amount of data in the RX FIFO (the I2C_BUFSTAT[13-8] RXSTAT bit field). The LH performs a number of data read accesses equal to the I2C_BUFSTAT[13-8] RXSTAT bit field (interrupt or polling mode), or reconfigures the DMA controller with the required value to drain the FIFO.

In controller transmit mode, if the TX FIFO threshold (the I2C_BUF[5-0] TXTRSH bit field value + 1) is not reached, but the amount of data remaining to be written in the TX FIFO is less than the threshold, the transmit draining interrupt (the I2C_IRQSTATUS_RAW[14] XDR bit) is asserted to inform the LH that it can read the amount of data remaining to be written in the TX FIFO (the I2C_BUFSTAT[5-0] TXSTAT bit field). The LH must write the required number of data bytes specified by the I2C_BUFSTAT[5-0] TXSTAT bit field value or reconfigure the DMA controller with the value required to transfer the last bytes to the FIFO.

In controller mode, the LH can alternately not check the values of the I2C_BUFSTAT[5-0] TXSTAT and I2C_BUFSTAT[13-8] RXSTAT bit fields, because it can obtain this information internally (by computing the I2C_CNT[15-0] DATACOUNT bit field value modulo I2C_BUF[13-8] RXTRSH or I2C_BUF[5-0] TXTRSH).

By default, the draining feature is disabled; it can be enabled using the I2C_IRQENABLE_SET[14] XDR_IE or I2C_IRQENABLE_SET[13] RDR_IE bits (default disabled) only for transfers with lengths not equal to the threshold values (I2C_BUF[5-0] TXTRSH bit field value + 1 for the TX threshold or the I2C_BUF[13-8] RXTRSH bit field value + 1 for the RX threshold).