Symphony DSP56724/DSP56725 Multi-Core Audio Processors, Rev. 0
10-6
Freescale Semiconductor
Serial Host Interface (SHI, SHI_1)
Figure 10-5. SHI I/O Shift Register (IOSR)
10.3.3
SHI Host Transmit Data Register (HTX)—DSP Side
The host transmit data register (HTX) is used for DSP-to-Host data transfers, and is 24 bits wide. Writing
to the HTX register using DSP core instructions or by DMA transfers clears the HTDE flag. The DSP may
program the HTIE bit to cause a host transmit data interrupt when the HTDE bit is set. (See
10.3.8.10, HCSR Transmit-Interrupt Enable (HTIE)—Bit 11.”
) To prevent overwriting the previous data,
data should not be written to the HTX register until the HTDE bit is set. The HTX register is reset to the
empty state when in stop mode, and also during hardware, software, and individual resets. In the different
data transfer modes, the following occurs:
•
In 8-bit data transfer mode, the most significant byte of the HTX register is transmitted.
•
In 16-bit data transfer mode, the two most significant bytes of the HTX register are transmitted.
•
In 24-bit data transfer mode, all the contents of HTX register are transferred.
10.3.4
SHI Host Receive Data FIFO (HRX)—DSP Side
The 24-bit host receive data FIFO (HRX) is a 10-word deep, First-In-First-Out (FIFO) register used for
Host-to-DSP data transfers. The serial data is received via the shift register and then loaded into the HRX
FIFO. In the different data transfer modes, the following actions occur:
•
In 8-bit data transfer mode, the most significant byte of the shift register is transferred to the HRX
FIFO (the other bits are cleared).
•
In 16-bit data transfer mode, the two most significant bytes are transferred (the least significant
byte is cleared) to the HTX FIFO.
•
In 24-bit data transfer mode, all 24 bits are transferred to the HRX FIFO.
The HRX FIFO may be read by the DSP while the HRX FIFO is being loaded from the shift register.
Reading all data from the HRX FIFO clears the HRNE flag. The HRX FIFO may be read using DSP core
instructions or by DMA transfers. The HRX FIFO is reset to the empty state when the chip is in stop mode,
and also during hardware reset, software, and individual resets.
16
23
8
15
0
7
Stops Data
When Data
Mode is Selected
24-Bit
Data Mode
Passes Data
When Data
Mode is Selected
16-Bit
Data Mode
8-Bit
Data Mode
Operating Mode
IOSR Register
Содержание Symphony DSP56724
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Страница 52: ...Symphony DSP56724 DSP56725 Multi Core Audio Processors Rev 0 2 30 Freescale Semiconductor Signal Descriptions ...
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