Details:

The OSPI Direct Access Controller (DAC) doesn’t support Continuous Read mode with NAND Flash since the OSPI controller can deassert the CSn signal (by design intent) to the Flash memory between internal DMA bus requests to the OSPI controller.

The issue occurs because “Continuous Read” mode offered by some OSPI/QSPI NAND Flash memories requires the Chip Select input to remain asserted for an entire burst transaction.

The SoC internal DMA controllers and other initiators are limited to 1023 B or smaller transactions, and arbitration/queuing can happen both inside of the various DMA controllers or in the interconnect between any DMA controller and the OSPI peripheral. This results in delays in bus requests to the OSPI controller that result in the external CSn signal being deasserted.

NOR Flash memories are not affected by CSn de-assertion and Continuous Read mode works as expected.

Workaround(s):

Software can use page/buffered read modes to access NAND flash.