Enhanced secure digital (SD) direct command for improved meta-channel communications

1. A method of improving meta-channel communications over a secure digital (SD) bus between an SD host and an SD client, the method comprising:

accessing, during a current data transfer over data lines of the SD bus, a first direct memory access (DMA) metadata and a second DMA metadata over a command (CMD) line of the SD bus using an enhanced SD direct command;

establishing, prior to a next data transfer over the data lines of the SD bus, a DMA configuration for the next data transfer based on the first DMA metadata and the second DMA metadata; and

communicating the next data transfer over the data lines of the SD bus according to the DMA configuration.

2. The method of claim 1 , further comprising:

embedding a first byte of DMA metadata in a first byte of the enhanced SD direct command as the first DMA metadata;

embedding a second byte of DMA metadata in a second byte of the enhanced SD direct command as the second DMA metadata; and

issuing the enhanced SD direct command to the SD client over the CMD line of the SD bus.

3. The method of claim 1 , in which accessing the first DMA metadata and the second DMA metadata comprises:

reading the first DMA metadata from a first byte of an enhanced SD direct response to the enhanced SD direct command; and

reading the second DMA metadata from a second byte of the enhanced SD direct response to the enhanced SD direct command.

4. The method of claim 1 , in which communicating comprises accessing a read packet through a direct memory access (DMA) channel indicated by the DMA configuration.

5. The method of claim 4 , in which accessing comprises:

reading the read packet through the DMA channel over the data lines of the SD bus from the SD client using an SD extended command; and

storing the read packet in a host buffer allocated according to the DMA configuration.

6. The method of claim 1 , in which the first DMA metadata and the second DMA metadata comprise a block count of a read packet and a DMA channel number to access the read packet from the SD client with an SD extended command.

7. The method of claim 6 , in which the SD extended command comprises a CMD53 command.

8. The method of claim 6 , in which the enhanced SD direct command comprises an enhanced CMD52 command.

9. The method of claim 1 , further comprising transmitting a write data packet from the SD host to the SD client over a DMA channel according to the DMA configuration.

10. The method of claim 1 , further comprising incorporating the SD bus between the SD host and the SD client into one of a computing system, a mobile computing device, an Internet of Things device, or virtual reality or augmented reality system.

11. An apparatus configured to improve meta-channel communications over a secure digital (SD) bus between an SD host and an SD client, the apparatus comprising:

a memory comprising an SD device; and

at least one processor coupled to the memory, the processor configured:

to access, during a current data transfer over data lines of the SD bus, a first direct memory access (DMA) metadata and a second DMA metadata over a command (CMD) line of the SD bus using an enhanced SD direct command;

to establish, prior to a next data transfer over the data lines of the SD bus, a DMA configuration for the next data transfer based on the first DMA metadata and the second DMA metadata; and

to communicate the next data transfer over the data lines of the SD bus according to the DMA configuration.

12. The apparatus of claim 11 , in which the processor is further configured:

to embed a first byte of DMA metadata in a first byte of the enhanced SD direct command as the first DMA metadata;

to embed a second byte of DMA metadata in a second byte of the enhanced SD direct command as the second DMA metadata; and

to issue the enhanced SD direct command to the SD client over the CMD line of the SD bus.

13. The apparatus of claim 11 , in which to access the first DMA metadata and the second DMA metadata, the processor is further configured:

to read the first DMA metadata from a first byte of an enhanced SD direct response to the enhanced SD direct command; and

to read the second DMA metadata from a second byte of the enhanced SD direct response to the enhanced SD direct command.

14. The apparatus of claim 11 , in which to communicate, the processor is further configured to access a read packet through a direct memory access (DMA) channel indicated by the DMA configuration.

15. The apparatus of claim 14 , in which to access, the processor is further configured:

to read the read packet through the DMA channel over the data lines of the SD bus from the SD client using an SD extended command; and

to store the read packet in a host buffer allocated according to the DMA configuration.

16. The apparatus of claim 11 , in which the first DMA metadata and the second DMA metadata comprise a block count of a read packet and a DMA channel number to access the read packet from the SD client with an SD extended command.

17. The apparatus of claim 16 , in which the SD extended command comprises a CMD53 command and the enhanced SD direct command comprises an enhanced CMD52 command.

18. A non-transitory computer-readable medium having program code recorded thereon to improve meta-channel communications over a secure digital (SD) bus between an SD host and an SD client, the program code executed by a processor and comprising:

program code to access, during a current data transfer over data lines of the SD bus, a first direct memory access (DMA) metadata and a second DMA metadata over a command (CMD) line of the SD bus using an enhanced SD direct command;

program code to establish, prior to a next data transfer over the data lines of the SD bus, a DMA configuration for the next data transfer based on the first DMA metadata and the second DMA metadata; and

program code to communicate the next data transfer over the data lines of the SD bus according to the DMA configuration.

19. The non-transitory computer-readable medium of claim 18 , in which the program code further comprises:

program code to embed a first byte of DMA metadata in a first byte of the enhanced SD direct command as the first DMA metadata;

program code to embed a second byte of DMA metadata in a second byte of the enhanced SD direct command as the second DMA metadata; and

program code to issue the enhanced SD direct command to the SD client over the CMD line of the SD bus.

20. The non-transitory computer-readable medium of claim 18 , in which the program code further comprises program code to transmit a write data packet from the SD host to the SD client over a DMA channel according to the DMA configuration.