AN2113 Freescale Semiconductor / Motorola, AN2113 Datasheet - Page 20

• Manufacturer Part Number: AN2113
• Description: AN2113 Multichannel Voice Coding System on the RTXC Operating System
• Manufacturer: Freescale Semiconductor / Motorola

Software Description
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7.5 RTXC
Using the mechanism shown in Figure 14, the hardware-specific ISR is isolated from the
application-specific sci_drv task. This makes it easier to reuse or migrate the application C code across
processors or applications. A similar mechanism transmits characters from the DSP56307 SCI to the host
as shown in Figure 15. As with the receive path, the SCI peripheral signals an event when a character is
ready to be transmitted, causing the SCI transmit ISR to execute. The SCI transmit ISR signals a
semaphore that enables the SCI output driver task sci_odrv. When the SCI output task executes, it
reads the output character from the RTXC output queue, which is then written to the SCI transmitter.
RTXC is a multitasking prioritizable, preemptive operating system. RTXC is treated as a software library,
so the application tasks and ISRs access the RTXC services by making calls to the RTXC API. Knowledge
of which inputs produce which outputs is all that is needed. The general form of the RTXC API call is
The character string
being mistakenly identified by the linker with some similarly named function in the run-time library of the
compiler. For example, the API call:
2. Signal Semaphore
KS_name ([arg1],[arg2], ... , [argN])
KS_wait(SSI_RISR)
3. Write Character
5. Read Character
KS_
1. SCI Rx Event
1. SCI Tx Event
identifies name as an RTXC kernel service. This prefix prevents name from
Freescale Semiconductor, Inc.
buffer
For More Information On This Product,
Multichannel Voice Coding System
Figure 15. SCI Transmitter
Figure 14. SCI Receiver
Go to: www.freescale.com
6. Enqueue Character
sci_idrv
SCI Rx
sci_odrv
3. Dequeue Character
ISR
Task
SCI
SCI Tx
Task
ISR
SCI
2. Read SCI receive register
Queue
4. Signal Semaphore
Input
4. Write SCI transmit register
Output
Queue