add SPI, not working yet (also need to set SPOL/SPHA etc)

F0:F030,F042,F072/usbcan_gpio/spi.c

@@ -0,0 +1,76 @@
+/*
+ * This file is part of the usbcangpio project.
+ * Copyright 2026 Edward V. Emelianov <edward.emelianoff@gmail.com>.
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+#include  <stm32f0.h>
+
+#include "hardware.h"
+#include "spi.h"
+
+// get best prescaler to fit given frequency
+static uint16_t get_baudrate_prescaler(uint32_t speed_hz){
+    uint32_t freq = peripherial_clock;
+    uint32_t best_i = 7;
+    uint32_t best_err = 0xFFFFFFFF;
+    for(int i = 0; i < 8; i++){
+        freq >>= 1;
+        uint32_t err = (freq > speed_hz) ? (freq - speed_hz) : (speed_hz - freq);
+        if(err < best_err){
+            best_err = err;
+            best_i = i;
+        }else if(err > best_err) break;
+    }
+    return best_i;
+}
+
+
+// Master, 8bit, CPOL=0, CPHA=0, MSB first
+void spi_setup(uint32_t speed){ // speed in Hz
+    RCC->APB2RSTR |= RCC_APB2RSTR_SPI1RST;
+    RCC->APB2RSTR = 0;
+    SPI1->CR1 = 0;
+    uint16_t br = get_baudrate_prescaler(speed);
+    SPI1->CR1 = SPI_CR1_MSTR | (br << 3) | SPI_CR1_SSM | SPI_CR1_SSI;
+    SPI1->CR2 = SPI_CR2_SSOE;
+    SPI1->CR1 |= SPI_CR1_SPE;
+}
+
+void spi_stop(){
+    SPI1->CR1 &= ~SPI_CR1_SPE;
+}
+
+// return -1 if SPI isn't run or got error
+int spi_transfer(const uint8_t *tx, uint8_t *rx, int len){
+    if(len < 1 || !(SPI1->CR1 & SPI_CR1_SPE)) return -1;
+    int i;
+    for(i = 0; i < len; ++i){
+        uint32_t timeout = 1000000;
+        while(!(SPI1->SR & SPI_SR_TXE)){
+            if (--timeout == 0) return -1; // error by timeout: TX isn't ready
+        }
+        uint8_t out = (tx) ? tx[i] : 0;
+        *(uint8_t*)&SPI1->DR = out; // ÚÁÐÉÓØ × DR
+        timeout = 1000000;
+        while(!(SPI1->SR & SPI_SR_RXNE)){
+            if(--timeout == 0) return 0;
+        }
+        uint8_t in = *(uint8_t*)&SPI1->DR; // ÞÔÅÎÉÅ ÉÚ DR
+        if(rx) rx[i] = in;
+    }
+    //while(SPI1->SR & SPI_SR_BSY){ }
+    return i;
+}