diff --git a/F3:F303/InterfaceBoard/Makefile b/F3:F303/InterfaceBoard/Makefile
index 6659b99..c98577d 100644
--- a/F3:F303/InterfaceBoard/Makefile
+++ b/F3:F303/InterfaceBoard/Makefile
@@ -3,6 +3,7 @@ BINARY		:= multiiface
 MCU			:= F303xc
 # change this linking script depending on particular MCU model,
 LDSCRIPT	:= stm32f303xB.ld
+# add define "-DSPIDMA" to use DMA for SSI encoder, in that case IF1 (USART3) would be interrupt-driven!
 DEFINES := -DUSB1_16
 
 include ../makefile.f3
diff --git a/F3:F303/InterfaceBoard/Readme.md b/F3:F303/InterfaceBoard/Readme.md
index 1a43a71..0d747be 100644
--- a/F3:F303/InterfaceBoard/Readme.md
+++ b/F3:F303/InterfaceBoard/Readme.md
@@ -104,7 +104,7 @@ Interfaces:
 
 DMA1 channels:
 
-- Ch2: USART3_Tx
+- Ch2: USART3_Tx or SPI1_Rx
 - Ch3: USART3_Rx
 - Ch4: USART1_Tx
 - Ch5: USART1_Rx
diff --git a/F3:F303/InterfaceBoard/hardware.c b/F3:F303/InterfaceBoard/hardware.c
index e6c2623..b00ad51 100644
--- a/F3:F303/InterfaceBoard/hardware.c
+++ b/F3:F303/InterfaceBoard/hardware.c
@@ -22,7 +22,7 @@ uint8_t Config_mode = 0;
 
 static inline void gpio_setup(){
     RCC->AHBENR |= RCC_AHBENR_GPIOAEN | RCC_AHBENR_GPIOBEN | RCC_AHBENR_GPIOCEN | RCC_AHBENR_GPIODEN
-                   | RCC_AHBENR_DMA1EN | RCC_AHBENR_DMA2EN;
+                   | RCC_AHBENR_DMA1EN | RCC_AHBENR_DMA2EN | RCC_APB2ENR_SPI1EN;
     RCC->APB1ENR |= RCC_APB1ENR_CANEN | RCC_APB1ENR_USART2EN | RCC_APB1ENR_USART3EN
                     | RCC_APB1ENR_UART4EN | RCC_APB1ENR_UART5EN;
     RCC->APB2ENR |= RCC_APB2ENR_USART1EN;
diff --git a/F3:F303/InterfaceBoard/main.c b/F3:F303/InterfaceBoard/main.c
index 89447ad..a102909 100644
--- a/F3:F303/InterfaceBoard/main.c
+++ b/F3:F303/InterfaceBoard/main.c
@@ -22,6 +22,7 @@
 #include "flash.h"
 #include "hardware.h"
 #include "proto.h"
+#include "spi.h"
 #include "strfunc.h"
 #include "usart.h"
 #include "usb_dev.h"
@@ -48,6 +49,7 @@ int main(void){
     USBPU_OFF();
     USB_setup();
     CAN_setup(the_conf.CANspeed);
+    spi_setup();
     //uint32_t ctr = Tms;
     //usb_LineCoding lc = {9600, 0, 0, 8};
     //for(int i = 0; i < 5; ++i) usart_config(i, &lc); // configure all U[S]ARTs for default data
@@ -63,13 +65,21 @@ int main(void){
             int l = USB_receive(i, (uint8_t*)inbuff, MAXSTRLEN);
             if(l) USB_send(i, (uint8_t*)inbuff, l);
         }*/
-        if(CDCready[ICAN]){
+        if(CDCready[ICAN]){ // process CAN bus
             int l = USB_receivestr(ICAN, inbuff, MAXSTRLEN);
             if(l < 0) USB_sendstr(ICAN, "ERROR: USB buffer overflow or string was too long\n");
             else if(l) CANcmd_parser(inbuff);
             canproto_process();
         }
-
+        if(CDCready[ISPI]){ // process encoder
+            if(USB_rcvlen(ISPI)){ // new data in USB - ask for new encoder data
+                if(spi_start_enc()) USB_receive(ISPI, (uint8_t*)inbuff, MAXSTRLEN); // clear incoming data
+            }
+            uint32_t val;
+            if(spi_read_enc(&val)){
+                USB_sendstr(ISPI, u2str(val));
+            }
+        }
         if(Config_mode && CDCready[ICFG]){
             /*if(Tms - ctr > 4999){
                 ctr = Tms;
diff --git a/F3:F303/InterfaceBoard/multiiface.bin b/F3:F303/InterfaceBoard/multiiface.bin
index 3ac4516..a55eb4c 100755
Binary files a/F3:F303/InterfaceBoard/multiiface.bin and b/F3:F303/InterfaceBoard/multiiface.bin differ
diff --git a/F3:F303/InterfaceBoard/multiiface.creator.user b/F3:F303/InterfaceBoard/multiiface.creator.user
index 0edb3ce..d728581 100644
--- a/F3:F303/InterfaceBoard/multiiface.creator.user
+++ b/F3:F303/InterfaceBoard/multiiface.creator.user
@@ -1,6 +1,6 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <!DOCTYPE QtCreatorProject>
-<!-- Written by QtCreator 18.0.2, 2026-02-19T23:09:57. -->
+<!-- Written by QtCreator 18.0.2, 2026-02-20T23:37:53. -->
 <qtcreator>
  <data>
   <variable>EnvironmentId</variable>
diff --git a/F3:F303/InterfaceBoard/multiiface.files b/F3:F303/InterfaceBoard/multiiface.files
index 66efa66..9b0bdaf 100644
--- a/F3:F303/InterfaceBoard/multiiface.files
+++ b/F3:F303/InterfaceBoard/multiiface.files
@@ -13,6 +13,8 @@ proto.c
 proto.h
 ringbuffer.c
 ringbuffer.h
+spi.c
+spi.h
 strfunc.c
 strfunc.h
 usart.c
diff --git a/F3:F303/InterfaceBoard/spi.c b/F3:F303/InterfaceBoard/spi.c
new file mode 100644
index 0000000..23609d1
--- /dev/null
+++ b/F3:F303/InterfaceBoard/spi.c
@@ -0,0 +1,108 @@
+/*
+ * This file is part of the multiiface 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 "Debug.h"
+#include "hardware.h"
+#include "spi.h"
+
+typedef enum{
+    SPI_NOTREADY,
+    SPI_IDLE,
+    SPI_READY,
+#ifdef SPIDMA
+    SPI_BUSY
+#endif
+} spiStatus;
+
+static spiStatus spi_status = SPI_NOTREADY;
+static uint32_t spidata = 0;
+
+#define WAITX(x)  do{volatile uint32_t  wctr = 0; while((x) && (++wctr < 360000)) IWDG->KR = IWDG_REFRESH; if(wctr==360000){ DBG("timeout"); return 0;}}while(0)
+
+// init SPI to work with and without DMA
+// DMA1Channel2 - SPI1 Rx
+void spi_setup(){
+    SPI1->CR1 = 0; // clear EN
+    SPI1->CR2 = 0;
+    // SPI for SSI: PA5/PA6, without MOSI; suppose that clocking and GPIO OK (hardware.c)
+    RCC->APB2RSTR = RCC_APB2RSTR_SPI1RST; // reset SPI before start
+    RCC->APB2RSTR = 0; // clear reset
+    SPI1->CR1 = SPI_CR1_SSM | SPI_CR1_SSI | SPI_CR1_RXONLY; // software slave management (without hardware NSS pin); RX only
+#ifdef SPIDMA
+    // setup SPI DMA
+    SPI11->CR2 = SPI_CR2_RXDMAEN;
+    // Rx
+    DMA1_Channel2->CPAR = (uint32_t)&(SPI1->DR);
+    DMA1_Channel2->CCR = DMA_CCR_MINC | DMA_CCR_TCIE | DMA_CCR_TEIE; // mem inc, hw->mem, Rx complete and error interrupt
+    NVIC_EnableIRQ(DMA1_Channel2_IRQn); // enable Rx interrupt
+#endif
+    // Master, baudrate = 0b110 - fpclk/128 (562.5 kHz)
+    SPI1->CR1 |= SPI_CR1_MSTR | SPI_CR1_BR_2 | SPI_CR1_BR_1;
+    // DS=8bit; RXNE generates after 8bit of data in FIFO;
+    SPI1->CR2 |= SPI_CR2_FRXTH | SPI_CR2_DS_2|SPI_CR2_DS_1|SPI_CR2_DS_0;
+    spi_status = SPI_IDLE;
+    DBG("SPI setup OK");
+}
+
+// return TRUE if data ready and change `encval`
+int spi_read_enc(uint32_t *encval){
+    if(spi_status != SPI_READY) return FALSE;
+    spi_status = SPI_IDLE;
+#ifndef SPIDMA
+    // clear SPI Rx FIFO
+    for(int i = 0; i < 4; ++i) (void) SPI1->DR;
+    SPI1->CR1 |= SPI_CR1_SPE;
+    uint8_t *data = (uint8_t*) &spidata;
+    for(uint32_t x = 0; x < ENCODERBYTES; ++x){
+        if(x == ENCODERBYTES - 1) SPI1->CR1 &= ~SPI_CR1_RXONLY; // clear RXonly bit to stop CLK generation after next byte
+        WAITX(!(SPI1->SR & SPI_SR_RXNE));
+        data[x] = *((volatile uint8_t*)&SPI1->DR);
+    }
+    SPI1->CR1 &= ~SPI_CR1_SPE;
+    SPI1->CR1 |= SPI_CR1_RXONLY; // and return RXonly bit
+#endif
+    if(encval) *encval = spidata;
+    return TRUE;
+}
+
+#ifdef SPIDMA
+// start encoder reading over DMA
+// @return FALSE if SPI is busy
+int spi_start_enc(){
+    if(spi_status == SPI_BUSY || spi_status == SPI_NOTREADY) return FALSE;
+    if(SPI1->SR & SPI_SR_BSY) return FALSE;
+    DMA1_Channel2->CMAR = (uint32_t) &spidata;
+    DMA1_Channel2->CNDTR = 4;
+    DMA1_Channel2->CCR |= DMA_CCR_EN;
+    SPI1->CR1 |= SPI_CR1_SPE;
+    spi_status = SPI_BUSY;
+    return TRUE;
+}
+
+// SSI got fresh data
+void dma1_channel2_isr(){
+    SPI1->CR1 &= ~SPI_CR1_SPE;
+    spi_status = SPI_READY; // ready independent on errors or Rx ready
+}
+#else
+int spi_start_enc(){ // simple stub
+    if(spi_status == SPI_NOTREADY) return FALSE;
+    spi_status = SPI_READY; // user asks to read data
+    return TRUE;
+}
+#endif
diff --git a/F3:F303/InterfaceBoard/spi.h b/F3:F303/InterfaceBoard/spi.h
new file mode 100644
index 0000000..72d78a7
--- /dev/null
+++ b/F3:F303/InterfaceBoard/spi.h
@@ -0,0 +1,27 @@
+/*
+ * This file is part of the multiiface 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/>.
+ */
+
+#pragma once
+#include <stm32f3.h>
+
+// amount of bytes to read from encoder
+#define ENCODERBYTES    4
+
+void spi_setup();
+int spi_start_enc();
+int spi_read_enc(uint32_t *encval);
diff --git a/F3:F303/InterfaceBoard/usart.c b/F3:F303/InterfaceBoard/usart.c
index c1a247a..6226a8b 100644
--- a/F3:F303/InterfaceBoard/usart.c
+++ b/F3:F303/InterfaceBoard/usart.c
@@ -52,7 +52,11 @@ typedef struct {
 // IF6[5]: (CAN)
 // IF7[6]: (SPI)
 static const USART_Config UC[USARTSNO] = {
+#ifdef SPIDMA
+    [0] = {.instance = USART3, .pclk_freq = 36000000, .UIRQn = USART3_IRQn, .dma_controller = NULL, .DEport = GPIOB, .DEpin = 1<<14 },
+#else
     [0] = {.instance = USART3, .pclk_freq = 36000000, .UIRQn = USART3_IRQn, .DIRQn = DMA1_Channel2_IRQn, .dma_controller = DMA1, .dma_rx_channel = DMA1_Channel3, .dma_tx_channel = DMA1_Channel2, .TTCflag = DMA_ISR_TCIF2, .DEport = GPIOB, .DEpin = 1<<14 },
+#endif
     [1] = {.instance = USART1, .pclk_freq = 72000000, .UIRQn = USART1_IRQn, .DIRQn = DMA1_Channel4_IRQn, .dma_controller = DMA1, .dma_rx_channel = DMA1_Channel5, .dma_tx_channel = DMA1_Channel4, .TTCflag = DMA_ISR_TCIF4, .DEport = GPIOB, .DEpin = 1<<0  },
     [2] = {.instance = USART2, .pclk_freq = 36000000, .UIRQn = USART2_IRQn, .DIRQn = DMA1_Channel7_IRQn, .dma_controller = DMA1, .dma_rx_channel = DMA1_Channel6, .dma_tx_channel = DMA1_Channel7, .TTCflag = DMA_ISR_TCIF7, .DEport = GPIOA, .DEpin = 1<<1  },
     [3] = {.instance = UART4,  .pclk_freq = 36000000, .UIRQn = UART4_IRQn,  .DIRQn = DMA2_Channel5_IRQn, .dma_controller = DMA2, .dma_rx_channel = DMA2_Channel3, .dma_tx_channel = DMA2_Channel5, .TTCflag = DMA_ISR_TCIF5 },
@@ -410,7 +414,9 @@ void uart4_exti34_isr(){  usart_isr(3); }
 void uart5_exti35_isr(){  usart_isr(4); }
 
 // DMA Tx interrupts (to arm ready flag)
+#ifndef SPIDMA
 void dma1_channel2_isr(){ TXrdy[0] = 1; DMA1->IFCR = DMA_IFCR_CTCIF2; }
+#endif
 void dma1_channel4_isr(){ TXrdy[1] = 1; DMA1->IFCR = DMA_IFCR_CTCIF4; }
 void dma1_channel7_isr(){ TXrdy[2] = 1; DMA1->IFCR = DMA_IFCR_CTCIF7; }
 void dma2_channel5_isr(){ TXrdy[3] = 1; DMA2->IFCR = DMA_IFCR_CTCIF5; }
diff --git a/F3:F303/InterfaceBoard/usb_dev.c b/F3:F303/InterfaceBoard/usb_dev.c
index 0bc3cd5..3fa8ab8 100644
--- a/F3:F303/InterfaceBoard/usb_dev.c
+++ b/F3:F303/InterfaceBoard/usb_dev.c
@@ -303,6 +303,10 @@ int USB_sendstr(uint8_t ifno, const char *string){
     return USB_send(ifno, (const uint8_t*)string, len);
 }
 
+int USB_rcvlen(uint8_t ifno){
+    return RB_datalen((ringbuffer*)&rbin[ifno]);
+}
+
 /**
  * @brief USB_receive - get binary data from receiving ring-buffer
  * @param buf (i) - buffer for received data
@@ -336,7 +340,7 @@ int USB_receivestr(uint8_t ifno, char *buf, int len){
     }
     int l = RB_readto((ringbuffer*)&rbin[ifno], '\n', (uint8_t*)buf, len);
     if(l < 1){
-        if(rbin[ifno].length == RB_datalen((ringbuffer*)&rbin[ifno])){ // buffer is full but no '\n' found
+        if(rbin[ifno].length >= RB_datalen((ringbuffer*)&rbin[ifno]) - 1){ // buffer is full but no '\n' found
             while(1 != RB_clearbuf((ringbuffer*)&rbin[ifno]));
             return -1;
         }
diff --git a/F3:F303/InterfaceBoard/usb_dev.h b/F3:F303/InterfaceBoard/usb_dev.h
index 303d30e..1b50818 100644
--- a/F3:F303/InterfaceBoard/usb_dev.h
+++ b/F3:F303/InterfaceBoard/usb_dev.h
@@ -61,6 +61,7 @@ int USB_send(uint8_t ifno, const uint8_t *buf, int len);
 //int USB_adddata(uint8_t ifno, const uint8_t *buf, int len);
 int USB_putbyte(uint8_t ifno, uint8_t byte);
 int USB_sendstr(uint8_t ifno, const char *string);
+int USB_rcvlen(uint8_t ifno);
 int USB_receive(uint8_t ifno, uint8_t *buf, int len);
 int USB_receivestr(uint8_t ifno, char *buf, int len);
 uint8_t IFconfig(uint8_t ifno, usb_LineCoding *l);
diff --git a/F3:F303/InterfaceBoard/version.inc b/F3:F303/InterfaceBoard/version.inc
index 30fb985..9542a9b 100644
--- a/F3:F303/InterfaceBoard/version.inc
+++ b/F3:F303/InterfaceBoard/version.inc
@@ -1,2 +1,2 @@
-#define BUILD_NUMBER "151"
-#define BUILD_DATE "2026-02-19"
+#define BUILD_NUMBER "154"
+#define BUILD_DATE "2026-02-20"