Texas Instruments TLV1562 manual Interrupt Driven Solution, Advantages, Disadvantages

Software Overview

8.4.1.3Interrupt Driven Solution

Usually, the most elegant solution is to use an interrupt procedure to control external signals. The problem for this application is the high speed. First, if more than a few words of code have to be executed between two samples, the software has to ensure that the first interrupts will be completed before the second interrupt is enabled. This can be done by globally disabling IRQs while executing one IRQ. The second problem is the interrupt latency. According to the pipeline architecture of the ’C54x, an interrupt routine is started at the earliest after three clock cycles (the last instruction in the pipeline will be executed before branching to the IRQ vector). Another processing overhead is the branch instruction from the original IRQ vector to the IRQ handler memory location.

In summary, the large number of instructions used to organize the interrupt and to branch from the actual code execution into the interrupt service routine will significantly use up resources.

Advantages:

•Data acquisition runs fully automated in the background; the main program (filtering, other controlling, etc.) does not need to control any data acquisition software flow.

•Easy software debugging and implementing of new features (not critical for any software changes)

•The software compensates for variations in timing given in data sheets for conversion and the real time until the flag goes high.

Disadvantages:

•Program overhead uses a lot of resources, which is critical for maximum throughput performance

•Watchdog algorithms needed to avoid a hang up of the ADC

8.4.1.4Enabling One Software Mode

Every main file (given later in this document), offers the following three switches in the program header:

SWITCH	DESCRIPTION
POLLING_DRV	software polls the INT0 pin until conversion is finished
INT0_DRIVEN	software uses Interrupt INT0 to organize conversion
NO_INT0_SIG	INT0 signal not in use, interface is controlled with timing solution

NOTE: Only one of the three switches is to be enabled.

Example: Run in interrupt driven mode:

POLLING_DRV .set 00000h

INT0_DRIVEN .set 00001h

NO_INT0_SIG .set 00000h

8.4.1.5Setting the Right Switches

As the software offers the choice of three conversion-end recognition strategies, it allows selection of other ADC-related features, such as the clock source, power save mode, or the resolution. Depending on the custom requirements of data throughput, the program header also defines whether the samples will be stored into memory, sent serially out to the TLC5618A DAC, or sent in parallel to the TLV5651 CommsDAC.

Interfacing the TLV1562 Parallel ADC to the TMS320C54x DSP 25