Texas Instruments Corporation

Fuk Ho Ng

Shivaling S Mahant-Shetti

Jonathan L Rowlands

Stephen (Hsiao Li

A data processing device 100 uses a portion of a random access memory 111 as an input buffer for holding a portion of a stream of data which is received by an input interface 130. Likewise, a portion of a memory 121 is used as an output buffer for holding a portion of processed data which is output by an output interface 140. A processing unit 110 within the processing device manages the flow of input and output data. The input interface asserts an I/O request 860 when it receives a data word, and the output interface asserts an I/O request 870 when it needs a data word. In response to an I/O request, fast interrupt circuitry inserts a ghost instruction which is formed by doppelganger circuitry into an instruction sequence which is being accessed from a ROM 112. The ghost instruction performs the requested data transfer.

Method and apparatus for providing fast interrupt response using a ghost

For subtracting two thermometer coded words each having a most significant byte (MSB) and a least significant byte (LSB), a check is made to see if a borrowing condition exists. A first borrowing condition exists if word B MSB is greater than word A MSB (12) and word A LSB is greater than word B LSB (14). In such a case a borrow (16) must take place on word B MSB. A second borrowing condition exists when word A MSB is greater than word B MSB (18) and word B LSB is greater than word A LSB (20). In this instance a borrow (22) must take place on word A MSB through a shift right function. After borrowing occurs, a subtraction process (24) takes place by exclusive-or'ing word A and B MSBs. The result is reconstructed (26) through a shift right process into proper thermometer code format. If a borrowing condition exists, an appropriate LSB is translated (28, 30) before an LSB subtraction process (32) takes the resulting word A and word B LSBs and exclusively-or's them together. The result is reconstructed (34) through a shift right rotate left process to place the LSB in proper thermometer code format. For addition, the first word is reversed (302) and added to the second word by an exclusive-or process. The result is inverted (306) and reconstructed (308) into proper thermometer code format. A carry (311) check is made and the reconstructed output is adjusted (310) whenever a carry condition exists. A further MSB adjustment (312) is made when the carry causes an overflow in the MSB result.

Growing community of inventors

Dallas, TX, United States of America

Fuk Ho Ng