CS494002 datasheet(55/100 Pages) CIRRUS

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6.2.7 Procedures for Parallel Host Mode

Communication for DSPAB

6.2.7.1 Control Write in a Parallel Host Mode

for DSPAB

When writing control data to DSPAB, the same

protocol is used whether the host is writing a

control message or an entire executable download

image. Messages sent to DSPAB should be written

most significant byte first. Likewise, downloads of

the application code should also be performed most

significant byte first.

The example shown in this section can be

generalized to fit any control write situation. The

generic function ‘Read_Byte_*()’ is used in the

following example as a generalized reference to

either Read_Byte_MOT() (read a byte in Motorola

mode) or Read_Byte_INT() (read a byte in Intel

mode), and ‘Write_Byte_*()’ is a generic reference

to Write_Byte_MOT() (write a byte in Motorola

mode) or Write_Byte_INT() (write a byte in Intel

mode). Figure 40 shows a typical write sequence.

The protocol presented in Figure 40 will now be

described in detail.

1) When the host is communicating with DSPAB,

the host must verify that DSPAB is ready to

accept a new control byte. If DSPAB has not

read the previous byte from the control port, it

will be unable to receive another byte.

2) In order to determine whether DSPAB is ready

to accept a new control byte the host must read

the HINBSY bit of the Host Control Register

(bit 2 in FA[1:0]=01b) using the selected

communication mode (Intel or Motorola). If

HINBSY is high, then the DSP is not prepared

to accept a new control byte, and the host

should poll the Host Control Register again. If

HINBSY is low, then the host may write a

control byte into the Host Message Register.

3) Once the host knows that the DSP is ready for

a new control byte, it should write the control

byte to the Host Message Register (FA[1:0] =

00b) using the selected communication mode

(Intel or Motorola).

4) If the host would like to write any more control

bytes to DSPAB, the host should once again

poll the Host Control Register (return to step 1).

6.2.7.2 Control Read in a Parallel Host Mode

for DSPAB

When reading control data from DSPAB, the same

protocol is used whether the host is reading a single

byte, a 6 byte message, or a string of messages.

During the boot procedure, a handshaking protocol

is used by DSPAB. This handshake consists of a 3

byte write to DSPAB followed by a 1 byte response

from the DSP. The host must read the response byte

and act accordingly. The boot procedure is

discussed in Section 8 “Boot Procedure” on page

71.

During

regular operation (at run-time), the

responses from DSPAB will always be 6 bytes in

length.

MORE BYTES

TO WRITE?

READ_BYTE_*(HOST

CONTROL REGISTER)

FINISHED

WRITE_BYTE_*(HOST

MESSAGE REGISTER)

HINBSY == 1

Figure 40. Typical Parallel Host Mode Control

Write Sequence Flow Diagram for DSPAB

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