Reported downstream at esphome/esphome#14312 — modbus commands time out on RTL8710BN since the libretiny bump from v1.10.0 to v1.12.1. TX works fine but RX never receives data. User confirmed v1.10.0 works and v1.12.1 doesnt.
The Serial library refactor split begin() into beginPrivate() + configure(). Looking at the code I think this may have reversed the initialization order relative to what the Realtek SDK documents. Havent been able to test this on hardware so this is just code analysis.
Realtek SDK documented order (from rtl8711b_uart.h):
4. UART_Init() — frame format
5. UART_SetBaud() — baud rate
6. UART_INTConfig() — enable IRQ
7. UART_RxCmd() — enable RX path
Old code (v1.10.0) — followed SDK order:
configure() → UART_Init() + UART_SetBaud()
VECTOR_IrqRegister/IrqEn
UART_RxCmd(ENABLE)
UART_INTConfig(RUART_IER_ERBI, ENABLE)
New code (v1.12.1) — reversed:
beginPrivate():
VECTOR_IrqRegister/IrqEn
UART_RxCmd(ENABLE) ← RX enabled first
UART_INTConfig(ERBI, ENABLE) ← IRQ enabled first
configure():
UART_Init() ← frame format AFTER
UART_SetBaud() ← baud rate AFTER
The call chain is in cores/common/arduino/libraries/api/Serial/Serial.cpp:
void SerialClass::begin(unsigned long baudrate, uint16_t config, pin_size_t rx, pin_size_t tx) {
this->end();
if (!this->setPins(rx, tx))
return;
if (!this->data) {
this->data = new SerialData();
this->rxBuf = new SerialRingBuffer();
}
this->beginPrivate(baudrate, config); // sets up IRQ + RX
this->configure(baudrate, config); // then calls UART_Init + SetBaud
}UART_Init() is a ROM function so cant inspect it directly. The theory is that if it resets the RX path or IER register as part of peripheral init, then RX would be dead after configure() runs. TX would still work because its polled, not interrupt-driven. This would match the reported symptom of modbus commands being sent but responses never arriving.
Could also be something else entirely in the refactor thats causing it — this is just the most suspicious change I found from reading the code.
Board: generic-rtl8710bx-4mb-980k (RTL8710BN)
Working: libretiny v1.10.0
Broken: libretiny v1.12.1
Reported downstream at esphome/esphome#14312 — modbus commands time out on RTL8710BN since the libretiny bump from v1.10.0 to v1.12.1. TX works fine but RX never receives data. User confirmed v1.10.0 works and v1.12.1 doesnt.
The Serial library refactor split
begin()intobeginPrivate()+configure(). Looking at the code I think this may have reversed the initialization order relative to what the Realtek SDK documents. Havent been able to test this on hardware so this is just code analysis.Realtek SDK documented order (from
rtl8711b_uart.h):Old code (v1.10.0) — followed SDK order:
New code (v1.12.1) — reversed:
The call chain is in
cores/common/arduino/libraries/api/Serial/Serial.cpp:UART_Init()is a ROM function so cant inspect it directly. The theory is that if it resets the RX path or IER register as part of peripheral init, then RX would be dead afterconfigure()runs. TX would still work because its polled, not interrupt-driven. This would match the reported symptom of modbus commands being sent but responses never arriving.Could also be something else entirely in the refactor thats causing it — this is just the most suspicious change I found from reading the code.
Board: generic-rtl8710bx-4mb-980k (RTL8710BN)
Working: libretiny v1.10.0
Broken: libretiny v1.12.1