chore: rewrite to modbus rtu

rs485.c

@@ -0,0 +1,43 @@
+#include "rs485.h"
+
+#include "ch32v003fun.h"
+
+#define RS485_DIR (1 << 0)
+
+void rs485_init(int uartBRR) {
+  RCC->APB2PCENR |= RCC_APB2Periph_GPIOD | RCC_APB2Periph_GPIOC |
+                    RCC_APB2Periph_USART1 | RCC_APB2Periph_AFIO;
+
+  // RS485_DIR as output, initial recv mode
+  GPIOC->CFGLR &= ~(0xf << (4 * 0));
+  GPIOC->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_PP) << (4 * 0);
+  GPIOC->BCR = RS485_DIR;
+
+  // UART pins (PD5=TX, PD6=RX)
+  GPIOD->CFGLR &= ~(0xf << (4 * 5) | 0xf << (4 * 6));
+  GPIOD->CFGLR |= (GPIO_Speed_10MHz | GPIO_CNF_OUT_PP_AF) << (4 * 5);
+  GPIOD->CFGLR |= GPIO_CNF_IN_FLOATING << (4 * 6);
+
+  USART1->CTLR1 =
+      USART_WordLength_8b | USART_Parity_No | USART_Mode_Tx | USART_Mode_Rx;
+  USART1->CTLR2 = USART_StopBits_1;
+  USART1->CTLR3 = USART_HardwareFlowControl_None;
+  USART1->BRR = uartBRR;
+  USART1->CTLR1 |= CTLR1_UE_Set;
+}
+
+void rs485_send(uint8_t *buf, uint16_t len) {
+  GPIOC->BSHR = RS485_DIR;  // TX mode
+
+  for (uint16_t i = 0; i < len; i++) {
+    while (!(USART1->STATR & USART_FLAG_TXE));
+    USART1->DATAR = buf[i];
+  }
+
+  while (!(USART1->STATR & USART_FLAG_TC));
+  GPIOC->BCR = RS485_DIR;  // RX mode
+}
+
+uint8_t rs485_available(void) { return (USART1->STATR & USART_FLAG_RXNE) != 0; }
+
+uint8_t rs485_read(void) { return USART1->DATAR & 0xFF; }