High quality Raspberry Pi I2S HAT - part 4

High quality Raspberry Pi I2S HAT - part 4 - OpenOCD programming

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 run the following command:

openocd -f /usr/local/share/openocd/scripts/interface/raspberrypi4.cfg -c “init; svf rpi2s3.svf” -c shutdown

After about 45s you should see something like this:

C ongrats, you have now programmed your Xilinx :)

Comments

High quality Raspberry Pi I2S HAT - part 1 - overview

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.

High quality Raspberry Pi I2S HAT - part 2 - hardware

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 12...

High quality Raspberry Pi I2S HAT - part 6 - conclusion

Now you have clean I2S signals, without using USB, SPDIF etc. :) This HAT was tested with different DAC's, oscillators and worked perfectly. On this picture with PCM5102 board (new post is coming):) P.S. I’ve made a small batch of this PCB and for those who wish to buy one, please do not hesitate to contact me via email.

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