Texas Instruments TMS320C67X/C67X+ DSP manual Example 5−1. Relocation of Interrupt Service Table

Overview

5.1.2.2Interrupt Service Table Pointer (ISTP)

The reset fetch packet must be located at address 0, but the rest of the IST can be at any program memory location that is on a 256-word boundary. The location of the IST is determined by the interrupt service table base (ISTB) field of the interrupt service table pointer register (ISTP). The ISTP is shown in Figure 2−11 (page 2-21) and described in Table 2−12. Example 5−1 shows the relationship of the ISTB to the table location.

Example 5−1. Relocation of Interrupt Service Table

(a) Relocating the IST to 800h

1)Copy the IST, located between 0h and 200h, to the memory location between 800h and A00h.

2) Write 800h to ISTP:	MVK 800h, A2
	MVC A2, ISTP
ISTP = 800h = 1000 0000 0000b

(b)How the ISTP directs the CPU to the appropriate ISFP in the relocated IST

Assume: IFR = BBC0h = 1011 1011 1100 0000b

IER = 1230h = 0001 0010 0011 0001b

2 enabled interrupts pending: INT9 and INT12

The 1s in the IFR indicate pending interrupts; the 1s in the IER indicate the interrupts that are enabled. INT9 has a higher priority than INT12, so HPEINT is encoded with the value for INT9, 01001b.

HPEINT corresponds to bits 9−5 of the ISTP:

ISTP = 1001 0010 0000b = 920h = address of INT9

0

800h

820h

840h

860h

880h

8A0h

8C0h

8E0h

900h

920h

940h

96h0

980h

9A0h

9C0h

9E0h

IST

RESET ISFP

RESET ISFP

NMI ISFP

Reserved

Reserved

INT4 ISFP

INT5 ISFP

INT6 ISFP

INT7 ISFP

INT8 ISFP

INT9 ISFP

INT10 ISFP

INT11 ISFP

INT12 ISFP

INT13 ISFP

INT14 ISFP

INT15 ISFP

Program memory

SPRU733 Interrupts 5-9