DMA engine

A circuit comprising:

• a central processing unit;
• an interface for accessing a slave device, the interface comprising a transmit buffer for transmitting to the slave device, a first-in-first-out receive buffer for receiving from the slave device, and an underflow mechanism associated with the first-in-first out receive buffer;
• a data transfer engine coupled between the interface and the central processing unit;
• and
• a memory, coupled to the central processing unit, storing code arranged to be executed on the central processing unit to set up the data transfer engine to access the slave device by:
• based on said set-up, operating the data transfer engine to supply a read request word to a slot of the transmit buffer of the interface for transmission to the slave device, said slave device generating a corresponding response word related to said read request word and, after return of said corresponding response word to the first-in-first-out receive buffer of the interface, to free said slot of said transmit buffer to disable said first-in-first-out receive buffer from receiving any further data such that the last word therein is assured to be said response word;
• and use the underflow mechanism of said first-in-first-out receive buffer to determine the last word therein and hence determine said response word.

A computer program product for accessing a slave device from a circuit comprising a central processing unit, a data transfer engine, and an interface to the slave device;

• the program comprising code stored on non-transient computer readable medium and configured so as when executed on the central processing unit to:
• set up the data transfer engine to access the slave device;
• based on said set-up, operate the data transfer engine to supply a read request word to a slot of a transmit buffer of the interface for transmission to the slave device, said slave device generating a corresponding response word related to said read request word and, after return of said corresponding response word to a first-in-first-out receive buffer of the interface, to free said slot of said transmit buffer to disable said first-in-first-out receive buffer from receiving any further data such that the last word therein is assured to be said response word;
• and
• use an underflow mechanism of said first-in-first-out receive buffer to determine the last word therein and hence determine said response word.