Hear-it! Solution Kit
R12UZ0012EG0110 Rev. 1.10
Page 25 of 34
Apr 03, 2017
The SSITX empty interrupt triggers DMAC0 channel to transfer data from the active tx buffer to the CODEC.
The DMAC0 transfer end interrupt handler updates the active sub-blocks for the g_pcm_buffer_tx and
g_pcm_buffer_rx buffers. It also requests more data to be read from the USB device to be stored at the current
receive buffer and triggers to transfer of data from the rx buffer to the tx buffer. The process is illustrated in
Figure 6-2.
Figure 6-2 : Data Transfer Scheme in USB Playback Mode
6.1.3
Volume Control
The volume of the audio signal is controlled by default by an attenuation function in software. This is called when
the audio block is transferred to the transmit buffer prior to transmission to the CODEC for output. Optionally,
the volume can be controlled directly by the CODEC, based on configuration in the source code. See section
5.3.2.2 for further details.
SSITX empty
interrupt
Transfer
End
Interrupt
DMAC0
isr_dmac_wr ()
Main routine: main()
Transmit buffer:
g_pcm_buffer_tx
Receive buffer:
g_pcm_buffer_rx
SSI
Module
N
ex
t
pc
m
_buf
fer
_r
x
infor
m
ati
on
N
ex
t
pc
m
_buf
fer
_tx
infor
m
ati
on
WM8983
CODEC
Data
Operation
Interrupt
us
b_data_fetc
h
fl
ag
Data fetc
h fr
om
US
B
Software
Attenuation
Function for
Volume Control
Summary of Contents for RX231
Page 34: ...RX231 Group R12UZ0012EG0110 ...
