AM625: UART with custom baudrate 1.333 MHz

Hi Vaibhav,

Thanks for the response. I tried your suggestions but non of them work.
1.333Mbps is very critical to the project and we need an expert assistance to get it right.

I was using am625-evk and I was using UART5 for testing. So, I enabled the UART5 and below is my patch

diff --git a/arch/arm64/boot/dts/ti/k3-am62x-sk-common.dtsi b/arch/arm64/boot/dts/ti/k3-am62x-sk-common.dtsi
index b1980b85c..32b50b081 100644
--- a/arch/arm64/boot/dts/ti/k3-am62x-sk-common.dtsi
+++ b/arch/arm64/boot/dts/ti/k3-am62x-sk-common.dtsi
@@ -15,6 +15,7 @@ aliases {
serial0 = &mcu_uart0;
serial1 = &wkup_uart0;
serial2 = &main_uart0;
+ serial5 = &main_uart5;
mmc0 = &sdhci0;
mmc1 = &sdhci1;
mmc2 = &sdhci2;
@@ -186,6 +187,13 @@ AM62X_IOPAD(0x1cc, PIN_OUTPUT, 0) /* (E14/E11) UART0_TXD */
>;
};

+ main_uart5_pins_default: main-uart5-pins-default {
+ pinctrl-single,pins = <
+ AM62X_IOPAD(0x01d8, PIN_INPUT, 1) /* (H21) MCAN0_TX.UART5_RXD */
+ AM62X_IOPAD(0x01dc, PIN_OUTPUT, 1) /* (E15) MCAN0_RX.UART5_TXD */
+ >;
+ };
+
main_i2c0_pins_default: main-i2c0-pins-default {
pinctrl-single,pins = <
AM62X_IOPAD(0x1e0, PIN_INPUT_PULLUP, 0) /* (B16/E12) I2C0_SCL */
@@ -348,6 +356,12 @@ &main_uart1 {
status = "reserved";
};

+&main_uart5 {
+ pinctrl-names = "default";
+ pinctrl-0 = <&main_uart5_pins_default>;
+ status = "okay";
+};
+
&main_i2c0 {
status = "okay";
pinctrl-names = "default";

1. I saw the clocktreetool for am62x www.ti.com/.../CLOCKTREETOOL
and found out there's a way to change the clock source of the uart. Instead of using the default 48 Mhz, I can use 127.6 Mhz.

If I do 16x then the baud rate with divisor value 6 = 1329166.67 which is very ideal to what I need. But, I do not know how to change it. I need your expertise on this. Please help me how to configure the clock.

2. I found out as well the UART has a clock (clock ID 2) DEV_UART5_FCLK_CLK_PARENT_HSDIV4_16FFT_MAIN_1_HSDIVOUT1_CLK that gives a clock frequency of 160000000

So, If I do 13x then the baud rate with divisor value 9 = 1367521.37

I changed the clock id to 2 so that the uart5 will run with 160Mhz clock.

diff --git a/arch/arm64/boot/dts/ti/k3-am62-main.dtsi b/arch/arm64/boot/dts/ti/k3-am62-main.dtsi
index 93d445cd8..4470fa78d 100644
--- a/arch/arm64/boot/dts/ti/k3-am62-main.dtsi
+++ b/arch/arm64/boot/dts/ti/k3-am62-main.dtsi
@@ -396,7 +396,8 @@ main_uart5: serial@2850000 {
reg = <0x00 0x02850000 0x00 0x100>;
interrupts = <GIC_SPI 183 IRQ_TYPE_LEVEL_HIGH>;
power-domains = <&k3_pds 156 TI_SCI_PD_EXCLUSIVE>;
- clocks = <&k3_clks 156 0>;
+ //clocks = <&k3_clks 156 0>;
+ clocks = <&k3_clks 156 2>;
clock-names = "fclk";
status = "disabled";
};

After I power cycled the board, I verified the uart5 clock is 160Mhz.  I ran:
cat /sys/class/tty/ttyS5/uartclk and it show: 160000000

I used this tool: github.com/.../linux-serial-test.git for verification

Note: We only care the UART RX but for the sake of testing, I used the TX to verify if the baud rate is correct
and verified by logic analyzer.

I ran the command below - just to verify if I can send data with the
linux-serial-test -p /dev/ttyS5 -d 9 -y 0xAA -f

Below is the screenshot of the logic analyzer and it showing error in framing.

Could you tell me what am I missing?.

Regards,

John

I figured out how to change the clock.

Hi John,

Thank you for your response.

This thread has been assigned to the correct expert.

Please expect responses in few business days.

Regards,
Vaibhav

Hi John,

John Tobias said:

linux-serial-test -p /dev/ttyS5 -d 9 -y 0xAA -f

Below is the screenshot of the logic analyzer and it showing error in framing.

Can you please measure the bit width in the logic analyzer capture to see what is the uart baud rate?

Hi John,

I think I am confused.

John Tobias said:

Instead of using the 48Mhz clock, I used 192Mhz clock and I was able to get the 1.333Mbps

Do you mean the issue is resolved now by using 192MHz clock?

Greetings John, Bin,

I think as per the new post from John: https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1383021/am625-m4-custom-baud-rate

This issue is resolved, so I am marking this thread resolved.

Regards,

Vaibhav