Revisions Affected

B, C

Details

The ADCINT flag can be set before the ADCRESULT value is latched (see the t_LAT and t_INT(LATE) columns in the ADC Timings table of the TMS320F2807x Real-Time Microcontrollers data sheet). The DMA can read the ADCRESULT value as soon as 3 cycles after the ADCINT trigger is set. As a result, the DMA could read a prior ADCRESULT value when the user expects the latest result if all of the following are true:

• The ADC is in late interrupt mode.
• The ADC operates in a mode where t_INT(LATE) occurs 3 or more cycles before t_LAT (ADCCTL2 [PRESCALE] > 2 for 12-bit mode).
• The DMA is triggered from the ADCINT signal.
• The DMA immediately reads the ADCRESULT value associated with that ADCINT signal without reading any other values first.
• The DMA was idle when it received the ADCINT trigger.

Only the DMA reads listed above could result in reads of stale data; the following non-DMA methods will always read the expected data:

• The ADCINT flag triggers a CLA task.
• The ADCINT flag triggers a CPU ISR.
• The CPU polls the ADCINT flag.

Workarounds

Trigger two DMA channels from the ADCINT flag. The first channel acts as a dummy transaction. This will result in enough delay that the second channel will always read the fresh ADC result.