Control Register File

2.7.10 Interrupt Service Table Pointer Register (ISTP)

The interrupt service table pointer register (ISTP) is used to locate the interrupt service routine (ISR). The ISTB field identifies the base portion of the address of the interrupt service table (IST) and the HPEINT field identifies the specific interrupt and locates the specific fetch packet within the IST. The ISTP is shown in Figure 2−11 and described in Table 2−12. See section 5.1.2.2 on page 5-9for a discussion of the use of the ISTP.

Figure 2−11.Interrupt Service Table Pointer Register (ISTP)

31

 

 

 

 

 

 

 

16

 

 

 

 

 

 

 

 

 

 

 

ISTB

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

R/W-0

 

 

 

 

 

 

15

10

9

5

4

3

2

1

0

 

 

 

 

 

 

 

 

 

ISTB

 

HPEINT

 

0

0

0

0

0

 

 

 

 

 

 

 

 

 

R/W-0

 

R-0

 

 

 

R-0

 

 

Legend: R = Readable by the MVC instruction; W = Writeable by the MVC instruction; -n= value after reset

Table 2−12. Interrupt Service Table Pointer Register (ISTP) Field Descriptions

Bit

Field

Value

Description

 

 

 

 

31−10

ISTB

0−3F FFFFh

Interrupt service table base portion of the IST address. This field is cleared

 

 

 

to 0 on reset; therefore, upon startup the IST must reside at address 0. After

 

 

 

reset, you can relocate the IST by writing a new value to ISTB. If relocated,

 

 

 

the first ISFP (corresponding to

 

is never executed via interrupt

 

 

 

RESET)

 

 

 

processing, because reset clears the ISTB to 0. See Example 5−1.

 

 

 

 

9−5

HPEINT

0−1Fh

Highest priority enabled interrupt that is currently pending. This field indicates

 

 

 

the number (related bit position in the IFR) of the highest priority interrupt (as

 

 

 

defined in Table 5−1 on page 5-3) that is enabled by its bit in the IER. Thus,

 

 

 

the ISTP can be used for manual branches to the highest priority enabled in-

 

 

 

terrupt. If no interrupt is pending and enabled, HPEINT contains the value 0.

 

 

 

The corresponding interrupt need not be enabled by NMIE (unless it is NMI)

 

 

 

or by GIE.

 

 

 

 

4−0

0

Cleared to 0 (fetch packets must be aligned on 8-word (32-byte) boundaries).

 

 

 

 

 

 

SPRU733

CPU Data Paths and Control

2-21

Page 47
Image 47
Texas Instruments TMS320C67X/C67X+ DSP manual Interrupt Service Table Pointer Register Istp