SWRU626 December 2025 CC3501E , CC3551E
In general, the M33 transmits data to the host packet-by-packet, i.e. packet N+1 is handled (i.e. copied from internal memory) only after packet N is ACKED. This also implies that CC35xx SDIO interface is a card with necessary read acknowledgement.
The diagram below describes the transport layer Host read:
Transfer is initiated by the card, asserting an IRQ line* to the host. Once the host sees this IRQ, it writes to a function #1 register, CLINTRD to clear the pending IRQ.
At this point in time host now issues command 53 for read packet payload:
| CMD53 | Function = #1 | Read Flag (0x0) | Mode = Block Mode | Block Count = [L/B] | Address = 0x0 (RX FIFO) |
After reading the entire packet, SDIO expects a read acknowledgment. The host does this by writing "0" to Packet read retransmission register. At this point in time, if the device has another packet to transmit to the host, it sets the IRQ line again, and the process repeats itself.