alexx DIY audio page

  Kernel patching At last, in order to make I2S Hat working properly you have to recompile the kernel. Firstly download kernel source files, suitable to your distribution. Secondly you can download the patches here . Copy and unpack in top directory kernel source. What are the patches doing? Here is the list: p1.patch - support for 384k in file ./sound/core/pcm_native.c p2.patch - support for 384 in file ./include/sound/pcm.h p3.patch - support for 384k in file ./sound/soc/codecs/pcm1794a.c p4.patch - gpio config in file ./arch/arm/boot/dts/overlays/rpi-dac-overlay.dts p5.patch - main driver file ./sound/soc/bcm/rpi-simple-soundcard.c p6.patch - support for 384k in file ./drivers/staging/vc04_services/bcm2835-audio/bcm2835-pcm.c To apply the patch you can use patch command as below: patch -p1 -i p1.patch Repeat this for all six patches. Then recompile and install new kernel and modules. Don't forget to add the line to config.txt Thats all

Ok, now is time to program XC9572XL First download and install OpenOCD: git clone git://git.code.sf.net/p/openocd/code openocd cd openocd/ ./bootstrap ./configure -–enable-sysfsgpio -–enable-bcm2835gpio make && make install The next step is to setup the configuration file. To do so, create a copy of the raspberrypi2-native config file: cp /usr/local/share/openocd/scripts/interface/ raspberrypi2-native.cfg /usr/local/share/openocd/scripts/interface/raspberrypi4.cfg Modify file raspberrypi4.cfg as follows: 1. uncomment and update “bcm2835gpio_jtag_nums 5 6 16 25” 2. comment  “bcm2835gpio_swd_nums” 3. add the line “adapter speed 100” 4. add the line "transport select jtag" 5. add the line "bcm2835gpio_peripheral_base 0xFE000000" 6. uncomment and update “bcm2835gpio_speed_coeffs 236181 60" You can download the modified file here . And now program your Xilinx directly, Navigate to the directory with svf the file in the terminal and ru

VHDL code VHDL code is very simple. It uses only one counter and few multiplexers: ---------------------------------------------------------------------------------- -- Company: -- Engineer: Alexx -- -- Create Date: 12:32:29 02/02/2020 -- Design Name: -- Module Name: top - Behavioral -- Project Name: -- Target Devices: -- Tool versions: -- Description: -- -- Dependencies: -- -- Revision: -- Revision 0.01 - File Created -- Additional Comments: -- ---------------------------------------------------------------------------------- library IEEE; use IEEE.STD_LOGIC_1164.ALL; -- Uncomment the following library declaration if using -- arithmetic functions with Signed or Unsigned values use IEEE.NUMERIC_STD.ALL; -- Uncomment the following library declaration if instantiating -- any Xilinx primitives in this code. library UNISIM; use UNISIM.VComponents.all; entity top is Port ( clock : in STD_LOGIC; data_i : in STD_LOGIC; clock44ena : out STD_LOGIC;

Schematic diagram You can download pdf version here . Schematic is very simple: Design consists of three main parts: Q1, Q2 oscillators 45/49Mhz, U4 - Xilinx CPLD - main logic and reclocker circuit build on U5, U6 and U7. Each part has its own LDO (U1, U2, U3). You can use many IC's in SOT23 package, also there is footprint on the PCB for bypass cap. In the prototype I'm using LP5907. X1 is the input of the external power supply. In case of an external supply, JP3 should be open. There is no need for a separate jtag port, as we will program Xilinx directly through Raspberry Pi gpio.   PCB           Assembled boards Here with ordinary oscillators and xc9572xl           And here with CCHD-957 from Crystek and xc9536xl             Here is the BOM: C1 47uF/10V SMB tantal. C2, C5, C18 2.2uF/25V 1206 X7R C3, C4, C19 10uF/16V 1206 X7R C6, C7, C8, C9,

As it is known the Raspberry Pi can output I2S signals but there are some big disadvantages resulting in poor sound quality. First of all, Rpi cannot output exact audio frequencies (44.1/48 and multiple) due to main oscillator - this causes lot of jitter in output I2S signals. Second of all, Rpi cannot output MCLK (master clock) and although this clock is beyond  I2S bus specification , is often needed by modern DAC chips. Basic idea is to run Rpi as SLAVE , exactly as shown here: Transmitter = Rpi Receiver = I2S HAT If we take high quality oscillators, all mentioned problems will disappear. But this idea requires kernel modification (HAT has to know the value of the actual sampling frequency). This whole project is divided into four subsections - hardware, VHDL code, OpenOCD program and GNU/Linux kernel modification.

Welcome to my DIY electronics audio page. Here you will find my DIY projects, measurements, mods, etc. I'm an electronic engineer working in R &D in a big company. Audio is my hobby ranging from designing input devices to listening to vinyl records and anything inbetween. Alexx