Hey all,
I have a source unit that uses an AK7738 IC and I would like to get the I2S signal straight from it using an 'I2S to SPDIF" converter board. I noticed the converter has the following inputs:
3 pin -----> MCLK master clock input
4 pin ----->LRCK clock input
5 pin -----> BCLK bit clock input
6 pin -----> SDATA data input
Im trying to fully understand the datasheet of the AK7738, and noticed it has several SDATA, BCLK, LRCK pins (SDATA1, 2, 3.. BLCK1, 2, 3..etc) and one MCLK pin so figure Ill stick to the #1 set first.
But now i noticed pins 20/21 are dual function and i dont know exactly to set them to output according to the tables below:
Im guessing at power-down (unit turned off?) both LRCK1 & BICK1 are set to input but when the unit's on is set to output? And SDOUT1 is output when unit's off but input when the unit's on?
* How can I make them all output when the unit's powered on? (guessing somehow set LRCK1 & BICK1 to H and maintain SDOUT1 to L)
Goal?
Its an Android head unit and would like to bypass the operating system and thus bypass Android's limitations
I have a source unit that uses an AK7738 IC and I would like to get the I2S signal straight from it using an 'I2S to SPDIF" converter board. I noticed the converter has the following inputs:
3 pin -----> MCLK master clock input
4 pin ----->LRCK clock input
5 pin -----> BCLK bit clock input
6 pin -----> SDATA data input
Im trying to fully understand the datasheet of the AK7738, and noticed it has several SDATA, BCLK, LRCK pins (SDATA1, 2, 3.. BLCK1, 2, 3..etc) and one MCLK pin so figure Ill stick to the #1 set first.
But now i noticed pins 20/21 are dual function and i dont know exactly to set them to output according to the tables below:
Im guessing at power-down (unit turned off?) both LRCK1 & BICK1 are set to input but when the unit's on is set to output? And SDOUT1 is output when unit's off but input when the unit's on?
* How can I make them all output when the unit's powered on? (guessing somehow set LRCK1 & BICK1 to H and maintain SDOUT1 to L)
Goal?
Its an Android head unit and would like to bypass the operating system and thus bypass Android's limitations
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IIUC that DSP chip has 5 independent I2S interfaces. It must have lots of config registers. I could not find any publicly available programming docs, the public datasheet is incomplete in this regard. The regs are configurable via the uP interface (SPI, I2C, ...), from the ARM SoC at android linux boot.
Google shows many android linux boot logs with ak7738, example of device tree config e.g. https://blog.csdn.net/wwttlili/article/details/103148895
If all you need is tapping the I2S output lines (from the ADCs), an oscilloscope should help you find which I2S block is active at output. But I am not sure it's really what you want as that would not bypass the android DSP only, but the whole SoC -> AK7738 -> analog amps path.
Google shows many android linux boot logs with ak7738, example of device tree config e.g. https://blog.csdn.net/wwttlili/article/details/103148895
If all you need is tapping the I2S output lines (from the ADCs), an oscilloscope should help you find which I2S block is active at output. But I am not sure it's really what you want as that would not bypass the android DSP only, but the whole SoC -> AK7738 -> analog amps path.
Hello @phofman, apologies for the late reply due to local holidays here.
But yes this DSP chip is very capable as it can be found on other high-end mobile audio devices like JL Audio VXi DSP/Amplifier. Thank you for confirming the configuration protocol it uses. Before even trying to figure that out I decided to tap into the i2s output from the ADCs on it.
Before I used oscilloscope, I looked at the entire board and noticed there were x2 TI PCM1754 DAC and x1 AKM 4387 ICs near it. I figured out that the 1754's are for front-LR & rear-LR and the 4387 is for the subwoofer. They all had the needed inputs ( SDATA, BCLK, LRCK, MCLK) and I traced each to the ak7738.
So I think I can just tap from the SDATA, BCLK, LRCK, MCLK inputs from one of the PCM1754's for my signal. Only concern is that there is a 11ohm resistor between the ak7738 & pcm1754, so I don't know if should put my tap before the resistor or bypass it and tap straight from the pcm1754 IC legs.
But yes this DSP chip is very capable as it can be found on other high-end mobile audio devices like JL Audio VXi DSP/Amplifier. Thank you for confirming the configuration protocol it uses. Before even trying to figure that out I decided to tap into the i2s output from the ADCs on it.
Before I used oscilloscope, I looked at the entire board and noticed there were x2 TI PCM1754 DAC and x1 AKM 4387 ICs near it. I figured out that the 1754's are for front-LR & rear-LR and the 4387 is for the subwoofer. They all had the needed inputs ( SDATA, BCLK, LRCK, MCLK) and I traced each to the ak7738.
So I think I can just tap from the SDATA, BCLK, LRCK, MCLK inputs from one of the PCM1754's for my signal. Only concern is that there is a 11ohm resistor between the ak7738 & pcm1754, so I don't know if should put my tap before the resistor or bypass it and tap straight from the pcm1754 IC legs.