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5.4
Data Transfer Methods
Peripheral I/O on the DSP56303 can be accomplished in three ways:
n
Polling
n
Interrupts
n
DMA
5.4.1
Polling
Polling is the easiest method for data transfers. When polling is chosen, the DSP56303 core
continuously checks a specified register flag waiting for an event to happen. One example
would be setting an overflow flag in one of the Timers. Once the event occurs, the DSP56303
is free to continue with its next task. However, while it is waiting for the event to occur, the
DSP56303 core is not executing any other code. Polling is the easiest transfer method since it
does not require register initialization, but it is also the least efficient use of the DSP core.
Each peripheral has its own set of flags which can be polled to determine when data is ready
to be transferred. For example, the ESSI control registers provide bits that tell the core when
data is ready to be transferred to or from the peripheral. The core polls these bits to determine
when to interact with the peripheral. Similar flags exist for each peripheral.
Example 5-1 shows software polling programmed in an application using the HI08.
jclr
move
In this example, the core waits until the Host Status Register (HSR) Host Transmit Data
Empty (HTDE) flag is set. When the flag is set, the core moves data from Y memory to the
X1 register.
5.4.2
Interrupts
Interrupts are more efficient than polling, but interrupts also require additional register
initialization. Polling requires the core to remain busy checking a flag in a specified control
register and therefore does not allow the core to execute other code at the same time. For
interrupts, you can initialize the interrupt so it is triggered off one of the same flags that can
also be polled. Then the core does not have to continuously check a flag. Once the interrupt is
initialized and the flag is set, the core is notified to execute a data transfer. Until the flag is set,
the core can remain busy executing other sections of code.
When an interrupt occurs, the core execution flow jumps to the interrupt start address defined
in Table B-3 in Appendix B, Programming Reference. It executes code starting at the
Example 5-1. Software Polling
#1,x:M_HSR,*
y:(TBUFF_PTR)+,x1
Programming the Peripherals
; loop if HSR[1]:HTDE=0
; move data to x1
Data Transfer Methods
5-3
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