I'm using a SoM with a STM32MP157C. I've connected a LTE modem to uart7, its connected with a 4-wire uart, going trough a level shifter. The device tree contains the following:
uart7_pins_mx: uart7_mx-0 {
pins1 {
pinmux = <STM32_PINMUX('E', 7, AF7)>, /* UART7_RX */
<STM32_PINMUX('E', 10, AF7)>; /* UART7_CTS */
bias-disable;
};
pins2 {
pinmux = <STM32_PINMUX('E', 8, AF7)>, /* UART7_TX */
<STM32_PINMUX('E', 9, AF7)>; /* UART7_RTS */
bias-disable;
drive-push-pull;
slew-rate = <0>;
};
};
uart7_sleep_pins_mx: uart7_sleep_mx-0 {
pins {
pinmux = <STM32_PINMUX('E', 7, ANALOG)>, /* UART7_RX */
<STM32_PINMUX('E', 8, ANALOG)>, /* UART7_TX */
<STM32_PINMUX('E', 9, ANALOG)>, /* UART7_RTS */
<STM32_PINMUX('E', 10, ANALOG)>; /* UART7_CTS */
};
};
and
&uart7{
pinctrl-names = "default", "sleep";
pinctrl-0 = <&uart7_pins_mx>;
pinctrl-1 = <&uart7_sleep_pins_mx>;
status = "okay";
/* USER CODE BEGIN uart7 */
uart-has-rtscts;
/* USER CODE END uart7 */
};
When I boot the device the RTS pin is high and it stays high. Reading the device buffer with "cat /dev/ttySTM1" does not cause the pin to go low. When i send a message with "echo "AT" > /dev/ttySTM1" the message "transmission complete is not set" is shown. The CTS pin coming from the modem is low, as expected. Running "cat /proc/tty/driver/stm32-usart" gives the following:
1: uart:stm32-usart mmio:0x40018000 irq:41 tx:12 rx:0 CTS|DSR|CD
I expect the RTS pin to be low, and only to go high when the device buffer is full, any ideas what is going wrong?
