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tac5

This repo describes PCBs and rp2040/rp2350 CircuitPython support for TI's TAC5xxx audio codecs. This code depends on extensions to CircuitPython's rp2pio library found in adafruit/circuitpython#9659.

  • pcm.py uses the rp2 PIO to implement a PCM interface to the TAC5 which supports arbitrary numbers of channels, word sizes, and sample rates.

  • tac5.py implements a TAC5 class which knows how to initialize the TAC5xxx over I2C, write to its DACs, and read from its ADCs.

  • If multiple TAC5xxx parts with different I2C addresses are present, they are assumed to be wired in parallel for multichannel operation and configured appropriately. In this mode, each chip uses one time slot in the DOUT signal and makes its DOUT Hi-Z at other times.

  • Chips are mounted on breakout boards. KiCad files for these boards are here. Schematic and layout look like this:

Playing multichannel audio files

If you have speakers attached to the codecs, multi-track audio files stored on an SD card accessible to the rp2040 can be played on the codecs as follows:

Adafruit CircuitPython 9.1.0-beta.3-252-g10dfea4284-dirty on 2024-11-07; Adafruit Feather RP2040 with rp2040
>>> import tac5
>>> t=tac5.TAC5()
>>> t.play('/count_8ch_32bit_16000Hz.raw')
playing...
opening /count_8ch_32bit_16000Hz.raw ...
repeating...
repeating...
repeating...
...

Codec test, analog loopback

In this example, 4 TAC5212's are connected with BCLK, FSYNC, DOUT, DIN, SCL, and SDA in parallel, and on each chip, the differential DAC outputs are connected to the differential ADC inputs to provide test signals for the ADCs, i.e. OUT1P -> IN1P, OUT1M -> IN1M, OUT2P -> IN2P, OUT2M -> IN2M.

Adafruit CircuitPython 9.1.0-beta.3-76-g2f62612186-dirty on 2024-07-18; Adafruit Feather RP2040 with rp2040
>>> 
>>> import tac5
>>> t = tac5.TAC5()
>>> t.play()
playing...
>>> t.record()
sample,record0,record1,record2,record3,record4,record5,record6,record7,
0,-1,-1,-1,-1,-21642,13829,-311,-14878,
1,22355,-20880,-14861,22749,-19762,8760,6829,-20253,
2,21608,-13819,-15930,23037,-17183,3144,13306,-22783,
3,18190,-3347,-16936,22962,-13994,-2666,18482,-22111,
4,10858,7951,-17876,22524,-10311,-8313,21849,-18332,
5,602,17291,-18745,21730,-6263,-13440,23074,-11979,
6,-8849,22352,-19541,20593,-1995,-17725,22040,-3945,
7,-17070,21881,-20257,19131,2341,-20896,18845,4634,
8,-21748,15993,-20896,17368,6597,-22754,13806,12577,
9,-22490,6149,-21452,15331,10620,-23182,7417,18743,
...(115 more lines)

When called without arguments, play() creates test output (right now sine waves of various frequencies separated by gaps) for each DAC channel and sets up the interface to repeatedly send the data to the DACs in the background. When record() is called without arguments, it creates a buffer the same size as the playing buffer, fills it with ADC samples, and prints out the returned data in CSV format. The table below compares the DAC outputs as seen on a scope with the ADC outputs plotted on a spreadsheet:

DAC output                                    ADC output

Digital loopback test, no codec, single buffered

  • This example shows how a loopback test can be used to test streaming data transfer when if a codec is not present. Connect DOUT to DIN.
Adafruit CircuitPython 9.1.0-beta.3-179-g1db7f36b79-dirty on 2024-10-24; Adafruit Feather RP2040 with rp2040
>>> import tac5
>>> t = tac5.TAC5(channels=2, width=8, sample_rate=12000, address=None)
>>> t.rec(length=10)
recording...
>>> t.play(length=10, test='count')
playing...
>>> t.show(t.record_loop_buffer)
'sample'; 'ch0'; 'ch1'
0; -10; -9
1; -8; -7
2; -6; -5
3; -4; -3
4; -2; -1
5; 0; 1
6; 2; 3
7; 4; 5
8; 6; 7
9; 8; 9
>>> t.show(t.play_loop_buffer, shift=False)
'sample'; 'ch0'; 'ch1'
0; -10; -9
1; -8; -7
2; -6; -5
3; -4; -3
4; -2; -1
5; 0; 1
6; 2; 3
7; 4; 5
8; 6; 7
9; 8; 9

Digital loopback test, no codec, double buffered

Note that the count test data generated by tac5 is offset by 1 in play_loop2_buffer to distinguish it from the other buffer's data.

Adafruit CircuitPython 9.1.0-beta.3-179-g1db7f36b79-dirty on 2024-10-24; Adafruit Feather RP2040 with rp2040
>>> import tac5
>>> t = tac5.TAC5(channels=2, width=8, sample_rate=12000, address=None)
>>> t.rec(length=10, double_buffer=True)
recording...
>>> t.play(length=10, test='count', double_buffer=True)
playing...
>>> t.show(t.record_loop_buffer)
'sample'; 'ch0'; 'ch1'
0; -9; -8
1; -7; -6
2; -5; -4
3; -3; -2
4; -1; 0
5; 1; 2
6; 3; 4
7; 5; 6
8; 7; 8
9; 9; 10
>>> t.show(t.record_loop2_buffer)
'sample'; 'ch0'; 'ch1'
0; -10; -9
1; -8; -7
2; -6; -5
3; -4; -3
4; -2; -1
5; 0; 1
6; 2; 3
7; 4; 5
8; 6; 7
9; 8; 9
>>> t.show(t.play_loop_buffer, shift=False)
'sample'; 'ch0'; 'ch1'
0; -10; -9
1; -8; -7
2; -6; -5
3; -4; -3
4; -2; -1
5; 0; 1
6; 2; 3
7; 4; 5
8; 6; 7
9; 8; 9
>>> t.show(t.play_loop2_buffer, shift=False)
'sample'; 'ch0'; 'ch1'
0; -9; -8
1; -7; -6
2; -5; -4
3; -3; -2
4; -1; 0
5; 1; 2
6; 3; 4
7; 5; 6
8; 7; 8
9; 9; 10

Digital loopback test, no codec, double buffered, recording to "tape"

Adafruit CircuitPython 9.1.0-beta.3-180-geda524f85c-dirty on 2024-10-24; Adafruit Feather RP2040 with rp2040
>>> import tac5
>>> t = tac5.TAC5(channels=2, width=8, sample_rate=12000, address=None)
>>> t.rec(length=10, double_buffer=True)
recording...
>>> t.play(length=10, test='count', double_buffer=True)
playing...
>>> t.show(t.record_loop_buffer)
'sample'; 'ch0'; 'ch1'
0; -9; -8
1; -7; -6
2; -5; -4
3; -3; -2
4; -1; 0
5; 1; 2
6; 3; 4
7; 5; 6
8; 7; 8
9; 9; 10
>>> t.tape('/foo.txt')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "tac5.py", line 347, in tape
KeyboardInterrupt: 
>>> import os
>>> os.stat('/foo.txt')
(32768, 0, 0, 0, 0, 0, 767760, 946685390, 946685390, 946685390)