SPRUIV7B May 2022 – September 2023 AM620-Q1 , AM623 , AM625 , AM625-Q1 , AM625SIP
Software is permitted to queue up to two indirect transfers for both the indirect write controller and the indirect read controller. Supporting two indirect operations allows a short turnaround time between the completion of one indirect operation and the start of the second. Any attempt to queue more than two operations will cause an interrupt to be generated. To take advantage of this feature, software should attempt to keep both indirect programming slots full at all times.
From the software perspective, indirect access queuing is achieved by triggering bit 0 of the indirect transfer control register (OSPI_INDIRECT_READ_XFER_CTRL_REG[0] START_FLD bit or OSPI_INDIRECT_WRITE_XFER_CTRL_REG[0] START_FLD bit) twice in short succession. The indirect number of bytes register (OSPI_INDIRECT_READ_XFER_NUM_BYTES_REG or OSPI_INDIRECT_WRITE_XFER_NUM_BYTES_REG register) and the indirect FLASH start address register (OSPI_INDIRECT_READ_XFER_START_REG or OSPI_INDIRECT_WRITE_XFER_START_REG register) must be setup with the relevant transfer data before START_FLD bit can be triggered for each transfer. Since these registers will change regularly, the hardware must keep sampled versions of these registers for the duration of the indirect transfer.
The internal register block will only issue an indirect start trigger to the key underlying datapath blocks one at a time. There are 2 independent datapath blocks in the indirect access controller that will receive and independently sample this information. The first is the datapath block on the data bus side of the SRAM. For indirect reads, this is a read interface, for indirect writes, it is a write interface. The second is the datapath block on the FLASH side of the SRAM. For indirect reads, this is a write interface, for indirect writes, it is a read interface. Both blocks will process the indirect transfers at different times. For example, for an indirect read operation, the datapath block on the FLASH side of the SRAM will be able to start processing the second queued transfer as soon as the last byte of the first transfer has been written to the SRAM. Before commencing the second transfer, this block must resample the OSPI_INDIRECT_READ_XFER_NUM_BYTES_REG and OSPI_INDIRECT_READ_XFER_START_REG registers. Similarly, the datapath block on the bus side will resample the same registers locally when it has forwarded all the FLASH data associated with the first indirect transfer from the SRAM onto the data bus.