diff --git a/V203F6P6/gsm/GsmDecoder.cpp b/V203F6P6/gsm/GsmDecoder.cpp
new file mode 100644
index 0000000..aca6a94
--- /dev/null
+++ b/V203F6P6/gsm/GsmDecoder.cpp
@@ -0,0 +1,38 @@
+#include "pwmclass.h"
+#include "GsmDecoder.h"
+
+static const unsigned int  DataLenght = 2529384u;
+extern "C" void * memcpy(void * dest, const void * src, size_t n);
+
+GsmDecoder::GsmDecoder(GpioClass & io) noexcept : OneWay<uint16_t>(),
+  led(io), flash(), gsm(), count(0u), pass(false) {
+}
+static constexpr int      INPUT_BIT_RANGE = 16;
+static constexpr unsigned SIGMA_MASK      = (1u << (INPUT_BIT_RANGE  + 0)) - 1u;
+static constexpr unsigned SIGNED_OFFEST   = (1u << (INPUT_BIT_RANGE  - 1));
+ // Předpokládá se na vstupu signed int o šířce INPUT_BIT_RANGE
+ // přičemž 0 na vstupu odpovídá MAXPWM / 2 na výstupu. Vypadá to divně, ale funguje.
+static unsigned pwm_sd (const int input) {
+  static unsigned sigma  = 0;   // podstatné je, že proměnná je statická
+  const  unsigned sample = (input + SIGNED_OFFEST) * MAXPWM;
+  sigma &= SIGMA_MASK;          // v podstatě se odečte hodnota PWM
+  sigma += sample;              // integrace prostým součtem
+  return sigma  >> INPUT_BIT_RANGE;
+}
+unsigned GsmDecoder::Send(uint16_t * dptr, const unsigned len) {
+  led << pass;
+  pass = ! pass;
+  const unsigned step = sizeof(gsm_frame);
+  static gsm_frame e;
+  flash.ReadBlock(count, e, step);
+  count += step;
+  gsm.decode (e, tmp_buf);
+  if (count >= DataLenght) count = 0u;
+  for (unsigned n=0u, k=0u; k<len; n++) {
+    const int16_t s = tmp_buf[n];
+    dptr [k++] = pwm_sd (s);    // vyzkoušená metoda jak vylepšit PWM
+    dptr [k++] = pwm_sd (s);    // pokud máme frekvenci PWM větší
+    dptr [k++] = pwm_sd (s);    // než vzorkovací frekvence signálu ft = n * fs, n = 3
+  }
+  return 0;
+}
diff --git a/V203F6P6/gsm/GsmDecoder.h b/V203F6P6/gsm/GsmDecoder.h
new file mode 100644
index 0000000..3e901f7
--- /dev/null
+++ b/V203F6P6/gsm/GsmDecoder.h
@@ -0,0 +1,22 @@
+#ifndef GSMDECODER_H
+#define GSMDECODER_H
+#include "gpio.h"
+#include "oneway.h"
+#include "gsm.h"
+#include "norflash.h"
+
+static constexpr int GSMLEN = 160;
+
+class GsmDecoder : public OneWay<uint16_t> {
+  GpioClass        & led;
+  NorFlash           flash;
+  GsmStatic          gsm;
+  unsigned           count;
+  bool               pass;
+  gsm_signal         tmp_buf [GSMLEN];
+  public:
+    explicit GsmDecoder(GpioClass & io) noexcept;
+    unsigned Send (uint16_t * ptr, const unsigned len) override;
+};
+
+#endif // GSMDECODER_H
diff --git a/V203F6P6/gsm/Makefile b/V203F6P6/gsm/Makefile
new file mode 100644
index 0000000..d711291
--- /dev/null
+++ b/V203F6P6/gsm/Makefile
@@ -0,0 +1,60 @@
+TARGET?= ch32v203
+
+TOOL  ?= gcc
+#TOOL  ?= clang
+
+PRJ    = example
+
+VPATH  = . ./$(TARGET)
+BLD    = ./build/
+DFLAGS = -d
+LFLAGS = -g
+LDLIBS =
+BFLAGS = --strip-unneeded
+
+CFLAGS = -MMD -Wall -Wno-parentheses -ggdb -fno-exceptions -ffunction-sections -fdata-sections
+CFLAGS+= -I. -I./$(TARGET) -I./common -I./lib/gsm/inc
+DEL    = rm -f
+
+# zdrojaky
+OBJS  = main.o pwmclass.o
+OBJS += GsmDecoder.o wrap.o
+OBJS += spiblocked.o norflash.o
+
+include $(TARGET)/$(TOOL).mk
+BOBJS = $(addprefix $(BLD),$(OBJS))
+
+all: $(BLD) $(PRJ).elf
+# ... atd.
+-include $(BLD)*.d
+LDLIBS += -L./lib -lgsm
+# linker
+$(PRJ).elf: $(BOBJS) ./lib/libgsm.a
+	-@echo [LD $(TOOL),$(TARGET)] $@
+	@$(LD) $(LFLAGS) -o $(PRJ).elf $(BOBJS) $(LDLIBS)
+	-@echo "size:"
+	@$(SIZE) $(PRJ).elf
+	-@echo "listing:"
+	$(DUMP) $(DFLAGS) $(PRJ).elf > $(PRJ).lst
+	-@echo "OK."
+	$(COPY) $(BFLAGS) -O binary $(PRJ).elf $(PRJ).bin
+# preloz co je potreba
+$(BLD)%.o: %.c
+	-@echo [CC $(TOOL),$(TARGET)] $@
+	@$(CC) -std=gnu99 -c $(CFLAGS) $< -o $@
+$(BLD)%.o: %.cpp
+	-@echo [CX $(TOOL),$(TARGET)] $@
+	@$(CXX) -std=c++17 -fno-rtti -c $(CFLAGS) $< -o $@
+$(BLD)%.o: %.s
+	-@echo [AS $(TOOL),$(TARGET)] $@
+	@$(AS) $(CCPU) $< -o $@
+$(BLD):
+	mkdir $(BLD)
+./lib/libgsm.a:
+	cd ./lib/gsm/src && $(MAKE) TARGET=$(TARGET) all
+flash: $(PRJ).elf
+	minichlink -w $(PRJ).bin flash -b
+# vycisti
+clean:
+	$(DEL) $(BLD)* *.lst *.bin *.elf *.map *~
+.PHONY: all clean flash run
diff --git a/V203F6P6/gsm/ch32v203 b/V203F6P6/gsm/ch32v203
new file mode 120000
index 0000000..7650c85
--- /dev/null
+++ b/V203F6P6/gsm/ch32v203
@@ -0,0 +1 @@
+../ch32v203/
\ No newline at end of file
diff --git a/V203F6P6/gsm/common b/V203F6P6/gsm/common
new file mode 120000
index 0000000..8332399
--- /dev/null
+++ b/V203F6P6/gsm/common
@@ -0,0 +1 @@
+../common/
\ No newline at end of file
diff --git a/V203F6P6/gsm/lib b/V203F6P6/gsm/lib
new file mode 120000
index 0000000..0ca1730
--- /dev/null
+++ b/V203F6P6/gsm/lib
@@ -0,0 +1 @@
+../../V203/gsm/lib/
\ No newline at end of file
diff --git a/V203F6P6/gsm/main.cpp b/V203F6P6/gsm/main.cpp
new file mode 100644
index 0000000..fd0560f
--- /dev/null
+++ b/V203F6P6/gsm/main.cpp
@@ -0,0 +1,22 @@
+#include "pwmclass.h"
+#include "GsmDecoder.h"
+#include "norflash.h"
+#include "oneway.h"
+#include "gpio.h"
+///////////////////////////////////////////////////////////
+/* GSM kecátko funguje i na tomto menším procesoru.
+ * Jen pak nusí být data v externí flash (připojené) přes
+ * SPI. Číst je je možné i v přerušení DMA, trvá to krátce.
+ * */
+///////////////////////////////////////////////////////////
+static PwmClass             pwm;
+static GpioClass            pwr (GPIOB, 8);
+static GsmDecoder           decoder (pwr);
+
+int main () {
+  pwr << true;
+  pwm.attach (decoder);
+  for (;;) {
+  }
+  return 0;
+}
diff --git a/V203F6P6/gsm/norflash.cpp b/V203F6P6/gsm/norflash.cpp
new file mode 100644
index 0000000..5f002b6
--- /dev/null
+++ b/V203F6P6/gsm/norflash.cpp
@@ -0,0 +1,45 @@
+#include "string.h"
+#include "norflash.h"
+
+/// Enumerace povelů pro SPI FLASH.
+enum FLASH_COMMANDS : uint8_t {
+  /* single byte commands */
+  FLASH_WRDI = 0x04,    // nepoužito
+  FLASH_WREN = 0x06,
+  FLASH_RDID = 0x9F,
+  FLASHRSTEN = 0x66,    // nepoužito
+  FLASH__RST = 0x99,    // nepoužito
+  FLASH__RES = 0xAB,    // release from power down, nepoužito
+  FLASH__DPD = 0xB9,    // power down, nepoužito
+  // multi - byte
+  FLASH_RDSR1 = 0x05,
+  // dále se mohou povely lišit
+  FLASH_RDSR2 = 0x35,   // nepoužito
+  FLASH_4READ = 0x03,
+  FLASH_4PP   = 0x02,
+  FLASH_4SE   = 0x20,
+};
+union FlashCommandHeader {
+  struct {
+    FLASH_COMMANDS cmd : 8;
+    uint32_t       adr : 24;       // adresa je BIG ENDIEN - vyšší byte vystupuje po SPI dříve (MSB FIRST).
+  }__attribute__((packed));
+  uint8_t bytes [4];
+}__attribute__((packed));
+static inline uint32_t be_set_24 (const uint32_t p) {
+  return  ((p & 0x000000ff) << 16)
+        | ((p & 0x0000ff00) <<  0)
+        | ((p & 0x00ff0000) >> 16);
+}
+/* Nic jiného zatím není potřeba, ale šlo by dodělat i zápis včetně mazání bloku.
+*/
+unsigned int NorFlash::ReadBlock(const unsigned int addr, uint8_t * data, const unsigned int len) {
+  FlashCommandHeader header;
+  header.cmd = FLASH_4READ;
+  header.adr = be_set_24(addr);
+  spi.ChipSelect(true);
+  for (unsigned n=0u; n<sizeof(header); n++) spi.ReadWriteByte(header.bytes[n]);
+  for (unsigned n=0u; n<len; n++) data [n] = spi.ReadWriteByte(0xff);
+  spi.ChipSelect(false);
+  return len;
+}
diff --git a/V203F6P6/gsm/norflash.h b/V203F6P6/gsm/norflash.h
new file mode 100644
index 0000000..098aaf7
--- /dev/null
+++ b/V203F6P6/gsm/norflash.h
@@ -0,0 +1,13 @@
+#ifndef NORFLASH_H
+#define NORFLASH_H
+#include <stdint.h>
+#include "spiblocked.h"
+
+class NorFlash {
+  SpiBlocked spi;
+  public:
+    explicit NorFlash () noexcept : spi() {}
+    unsigned ReadBlock (const unsigned addr, uint8_t * data, const unsigned len);
+};
+
+#endif // NORFLASH_H
diff --git a/V203F6P6/gsm/pwmclass.cpp b/V203F6P6/gsm/pwmclass.cpp
new file mode 100644
index 0000000..a932938
--- /dev/null
+++ b/V203F6P6/gsm/pwmclass.cpp
@@ -0,0 +1,107 @@
+#include "pwmclass.h"
+#include "gpio.h"
+typedef __SIZE_TYPE__ size_t;
+extern "C" {
+  [[gnu::interrupt]] extern void DMA1_Channel2_IRQHandler( void );
+};
+static PwmClass * pPwmInstance = nullptr;
+void DMA1_Channel2_IRQHandler( void ) {
+  DMA1_Type::INTFR_DEF state (DMA1.INTFR);
+  if (state.B.GIF2 != RESET) {
+    DMA1.INTFCR.B.CGIF2 = SET;
+  } else return;
+  if (state.B.HTIF2 != RESET) {
+    DMA1.INTFCR.B.CHTIF2 = SET;
+    if (pPwmInstance) pPwmInstance->send(false);
+  }
+  if (state.B.TCIF2 != RESET) {
+    DMA1.INTFCR.B.CTCIF2 = SET;
+    if (pPwmInstance) pPwmInstance->send(true);
+  }
+}
+/*
+ * initialize TIM2 for PWM
+ */
+inline void PwmClass::TimInit() noexcept {
+	// Enable GPIOA and TIM1
+  RCC.APB2PCENR.modify([] (RCC_Type::APB2PCENR_DEF & r) -> auto {
+    r.B.IOPAEN = SET;
+    r.B.IOPBEN = SET;
+  //r.B.AFIOEN = SET;
+    return r.R;
+  });
+  RCC.APB1PCENR.B.TIM2EN = SET;
+    // PA2 is TIM2_CH3, 10MHz Output alt func, push-pull
+  GPIOA.CFGLR.modify([](GPIOA_Type::CFGLR_DEF & r) -> auto {
+    r.B.CNF2  = 2u;
+    r.B.MODE2 = 1u;
+    return r.R;
+  });
+    // PB1 is DEN, active H Output 10 MHz, push-pull
+  GPIOB.CFGLR.modify([](GPIOA_Type::CFGLR_DEF & r) -> auto {
+    r.B.CNF1  = 0u;
+    r.B.MODE1 = 1u;
+    return r.R;
+  });
+  GPIOB.BSHR.B.BS1 = SET; // set to H
+	// Reset TIM2 to init all regs
+  RCC.APB1PRSTR.B.TIM2RST = SET;
+  RCC.APB1PRSTR.B.TIM2RST = RESET;
+	// CTLR1: default is up, events generated, edge align
+	// SMCFGR: default clk input is CK_INT
+	// Prescaler 
+  TIM2.PSC.R = 0u;                // 144 MHz
+	// Auto Reload - sets period
+  TIM2.ATRLR.R = MAXPWM - 1;      // 24 kHz
+  
+	// CH3 Mode is output, PWM1 (CC3S = 00, OC3M = 110)
+  TIM2.CHCTLR2_Output.modify([](TIM2_Type::CHCTLR2_Output_DEF & r) -> auto {
+    r.B.OC3M  = 0x6u;
+    return r.R;
+  });
+	// Enable TIM1 outputs
+  TIM2.CCER.modify([](TIM2_Type::CCER_DEF & r) -> auto {
+	// Enable CH3, CH3 output, positive pol
+    r.B.CC3E  = SET;
+  //r.B.CC3P  = SET;  // negative
+    return r.R;
+  });
+	// Reload immediately + Trigger DMA
+  TIM2.SWEVGR.B.UG     = SET;
+  TIM2.DMAINTENR.B.UDE = SET;
+}
+inline void PwmClass::DmaInit() noexcept {
+	// Enable DMA
+  RCC.AHBPCENR.modify([](RCC_Type::AHBPCENR_DEF & r) -> auto {
+    r.B.SRAMEN = SET;
+    r.B.DMA1EN = SET;
+    return r.R;
+  });
+	// DMA can be configured to attach to T2UP
+	// The system can only DMA out at ~2.2MSPS.  2MHz is stable.
+  DMA1.CNTR2 .R = FULL_LEN;
+  DMA1.MADDR2.R = reinterpret_cast<size_t>(buffer);
+  DMA1.PADDR2.R = reinterpret_cast<size_t>(& TIM2.CH3CVR);
+  NVIC.EnableIRQ (DMA1_Channel2_IRQn);
+  DMA1.CFGR2.modify([](DMA1_Type::CFGR2_DEF & r) -> auto {
+    r.B.DIR   = SET;                    // MEM2PERIPHERAL
+    r.B.PL    = 2u;                     // High priority.
+    r.B.PSIZE = 1u;                     // 16-bit peripheral
+    r.B.MSIZE = 1u;                     // 16-bit memory
+    r.B.MINC  = SET;                    // Increase memory.
+    r.B.CIRC  = SET;                    // Circular mode.
+    r.B.HTIE  = SET;                    // Half-trigger
+    r.B.TCIE  = SET;                    // Whole-trigger
+    // Enable DMA1 CH2
+    r.B.EN    = SET;
+    return r.R;
+  });
+}
+
+PwmClass::PwmClass() noexcept : count(0u), pL(buffer), pH(buffer + HALF_LEN), src(nullptr) {
+  pPwmInstance = this;
+  TimInit ();
+  DmaInit ();
+	// Enable TIM2
+  TIM2.CTLR1.B.CEN = SET;
+}
diff --git a/V203F6P6/gsm/pwmclass.h b/V203F6P6/gsm/pwmclass.h
new file mode 100644
index 0000000..3572de2
--- /dev/null
+++ b/V203F6P6/gsm/pwmclass.h
@@ -0,0 +1,35 @@
+#ifndef PWMCLASS_H
+#define PWMCLASS_H
+#include "system.h"
+#include "oneway.h"
+  static constexpr unsigned MAXPWM   = 6000u;
+/* Používá TIM2, PWM kanál 3, DMA1 kanál 2, přerušení DMA1_Channel2_IRQHandler */
+class PwmClass {
+  static constexpr unsigned HALF_LEN = 3u * 160u;
+  static constexpr unsigned FULL_LEN = 2u * HALF_LEN;
+  volatile unsigned  count;
+  uint16_t * const   pL;
+  uint16_t * const   pH;
+  uint16_t           buffer [FULL_LEN];
+  OneWay<uint16_t> * src;
+  public:
+    explicit PwmClass () noexcept;
+    void attach (OneWay<uint16_t> & s) { src = & s; }
+    void send (const bool b) {
+      if (!src) return;
+      if (b) src->Send (pH, HALF_LEN);
+      else   src->Send (pL, HALF_LEN);
+      if (count) count -= 1u;
+    }
+    void delay (const unsigned frames = 50u) {
+      count = frames;
+      while (count) {
+        asm volatile ("nop");
+      }
+    }
+  protected:
+    void DmaInit () noexcept;
+    void TimInit () noexcept;
+};
+
+#endif // PWMCLASS_H
diff --git a/V203F6P6/gsm/spiblocked.cpp b/V203F6P6/gsm/spiblocked.cpp
new file mode 100644
index 0000000..77576ab
--- /dev/null
+++ b/V203F6P6/gsm/spiblocked.cpp
@@ -0,0 +1,66 @@
+#include "system.h"
+#include "spiblocked.h"
+enum SPICLK : uint32_t {
+  FPCLK_2 = 0u, // 72 MHz
+  FPCLK_4,      // 36 MHz
+  FPCLK_8,      // 18 MHz
+  FPCLK_16,     // 9  MHz
+  FPCLK_32,     // 4.5    MHz
+  FPCLK_64,     // 2.25   MHz
+  FPCLK_128,    // 1.125  MHz
+  FPCLK_256,    // 0.5625 MHz
+};
+static constexpr unsigned FM = 3u; // 50 MHz
+static void InitPins () noexcept {
+  // PA4 - NSS, PA5 - SCK, PA6 - MISO, PA7 - MOSI
+  GPIOA.CFGLR.modify([](GPIOA_Type::CFGLR_DEF & r) -> uint32_t {
+    r.B.MODE4 = FM;
+    r.B.CNF4  = 0u; // gen push - pull
+    r.B.MODE5 = FM;
+    r.B.CNF5  = 2u; // alt push - pull
+    r.B.MODE6 = 0u; // input mode
+    r.B.CNF6  = 1u; // floating
+    r.B.MODE7 = FM;
+    r.B.CNF7  = 2u; // alt push - pull
+    return r.R;
+  });
+  // AFIO - default
+  GPIOA.BSHR.B.BS4 = SET;
+}
+
+SpiBlocked::SpiBlocked() noexcept {
+  RCC.APB2PCENR.modify([](RCC_Type::APB2PCENR_DEF & r) -> uint32_t {
+    r.B.SPI1EN = SET;
+    r.B.IOPAEN = SET;
+  //r.B.AFIOEN = SET;
+    return r.R;
+  });
+  InitPins();
+  RCC.APB2PRSTR.B.SPI1RST = SET;
+  RCC.APB2PRSTR.B.SPI1RST = RESET;
+  SPI1.CTLR1.modify([](SPI1_Type::CTLR1_DEF & r) -> uint32_t {
+    r.B.CPHA     = RESET;
+    r.B.CPOL     = RESET;
+    r.B.MSTR     = SET;       // master
+    r.B.DFF      = RESET;     // 8 bit
+    r.B.SSM      = SET;       // software
+    r.B.SSI      = SET;       // !!! netuším proč, ale jinak se nenastaví MSTR a SPE
+    r.B.LSBFIRST = RESET;
+    r.B.BR       = FPCLK_64;
+    return r.R;
+  });
+  SPI1.CRCR.R      = 7u;
+  SPI1.CTLR1.B.SPE = SET;
+}
+uint8_t SpiBlocked::ReadWriteByte(const uint8_t data) {
+  while (SPI1.STATR.B.TXE  == RESET);
+  SPI1.DATAR.B.DATAR = data;
+  while (SPI1.STATR.B.RXNE == RESET);
+  return SPI1.DATAR.B.DATAR;
+}
+void SpiBlocked::ChipSelect(const bool on) {
+  if (on) GPIOA.BSHR.B.BR4 = SET;
+  else    GPIOA.BSHR.B.BS4 = SET;
+}
+
+
diff --git a/V203F6P6/gsm/spiblocked.h b/V203F6P6/gsm/spiblocked.h
new file mode 100644
index 0000000..4ca59c9
--- /dev/null
+++ b/V203F6P6/gsm/spiblocked.h
@@ -0,0 +1,12 @@
+#ifndef SPIBLOCKED_H
+#define SPIBLOCKED_H
+#include <stdint.h>
+
+class SpiBlocked {
+public:
+  explicit SpiBlocked () noexcept;
+  uint8_t ReadWriteByte (const uint8_t data);
+  void    ChipSelect    (const bool on);
+};
+
+#endif // SPIBLOCKED_H
diff --git a/V203F6P6/gsm/wrap.c b/V203F6P6/gsm/wrap.c
new file mode 100644
index 0000000..bb42b02
--- /dev/null
+++ b/V203F6P6/gsm/wrap.c
@@ -0,0 +1,22 @@
+/* Funkce z newlib, použité ve zdrojácích.
+ * Velmi zjednodušeno.
+ */
+typedef struct {
+  int quot, rem;
+} div_t;
+typedef __SIZE_TYPE__ size_t;
+div_t div (int numerator, int denominator) {
+  const div_t result = { numerator / denominator, numerator % denominator };
+  return result;
+}
+void * memset(void * s, int c, size_t n) {
+  char * p = (char*) s;
+  for (unsigned i=0u; i<n; i++) p [i] = c;
+  return s;
+}
+void * memcpy(void * dest, const void * src, size_t n) {
+  char * d = (char*) dest;
+  const char * s = (const char*) src;
+  for (unsigned i=0u; i<n; i++) d [i] = s [i];
+  return dest;
+}