diff --git a/README.md b/README.md
index bba57f6..e62f176 100644
--- a/README.md
+++ b/README.md
@@ -8,7 +8,7 @@ This program generates an FM modulation, with RDS (Radio Data System) data gener
 
 It is based on the FM transmitter created by [Oliver Mattos and Oskar Weigl](http://www.icrobotics.co.uk/wiki/index.php/Turning_the_Raspberry_Pi_Into_an_FM_Transmitter), and later adapted to using DMA by [Richard Hirst](https://github.com/richardghirst). Christophe Jacquet adapted it and added the RDS data generator and modulator. The transmitter uses the Raspberry Pi's PWM generator to produce VHF signals.
 
-It is compatible with both the Raspberry Pi 1 (the original one) and the Raspberry Pi 2, 3 and 3+.
+It is compatible with both the Raspberry Pi 1 (the original one) and the Raspberry Pi 2, 3 and 4.
 
 ![](doc/vfd_display.jpg)
 
diff --git a/src/Makefile b/src/Makefile
index 6cebd28..7e35ed7 100644
--- a/src/Makefile
+++ b/src/Makefile
@@ -1,24 +1,32 @@
 CC = gcc
-STD_CFLAGS = -Wall -std=gnu99 -c -g -O3
+STD_CFLAGS = -Wall -std=gnu99 -c -g
 
 # Enable ARM-specific options only on ARM, and compilation of the app only on ARM
 UNAME := $(shell uname -m)
 
-# Determine the hardware platform. Below, pi1 stands for the RaspberryPi 1 (the original one),
-# and pi2 stands for both the RaspberryPi 2 and 3.
+# Determine Raspberry Pi version (if 2 or greater)
+RPI_VERSION := $(shell cat /proc/device-tree/model | grep -a -o "Raspberry\sPi\s[0-9]" | grep -o "[0-9]")
+
+# Determine the hardware platform and set proper compilation flags
 ifeq ($(UNAME), armv6l)
-	CFLAGS = $(STD_CFLAGS) -march=armv6 -mtune=arm1176jzf-s -mfloat-abi=hard -mfpu=vfp -ffast-math -DRASPI=1
-	TARGET = pi1
-else ifeq ($(UNAME), armv7l)
-	CFLAGS = $(STD_CFLAGS) -march=armv7-a -mtune=arm1176jzf-s -mfloat-abi=hard -mfpu=vfp -ffast-math -DRASPI=2
-	TARGET = pi2
-else ifeq ($(UNAME), aarch64)
-	CFLAGS = $(STD_CFLAGS) -march=armv8-a -O2 -pipe -fstack-protector-strong -fno-plt -ffast-math -DRASPI=2
-	TARGET = pi2
+	ARCH_CFLAGS = -march=armv6 -O3 -mtune=arm1176jzf-s -mfloat-abi=hard -mfpu=vfp -ffast-math
+	TARGET = 1
+else ifeq ($(shell expr $(RPI_VERSION) \> 1), 1)
+	ifeq ($(UNAME), armv7l)
+		ARCH_CFLAGS = -march=armv7-a -O3 -mtune=arm1176jzf-s -mfloat-abi=hard -mfpu=vfp -ffast-math
+	else ifeq ($(UNAME), aarch64)
+		ARCH_CFLAGS = -march=armv8-a -O2 -pipe -fstack-protector-strong -fno-plt -ffast-math
+	endif
+	ifeq ($(shell expr $(RPI_VERSION) \>= 4), 1)
+		TARGET = 4
+	else
+		TARGET = 2
+	endif
 else
-	CFLAGS = $(STD_CFLAGS)
+	ARCH_CFLAGS = -O3
 	TARGET = other
 endif
+CFLAGS = $(STD_CFLAGS) $(ARCH_CFLAGS) -DRASPI=$(TARGET)
 
 ifneq ($(TARGET), other)
 
diff --git a/src/pi_fm_rds.c b/src/pi_fm_rds.c
index b8e91b8..7423869 100644
--- a/src/pi_fm_rds.c
+++ b/src/pi_fm_rds.c
@@ -116,11 +116,19 @@
 #define PERIPH_PHYS_BASE 0x7e000000
 #define DRAM_PHYS_BASE 0x40000000
 #define MEM_FLAG 0x0c
+#define PLLFREQ 500000000.
 #elif (RASPI)==2
 #define PERIPH_VIRT_BASE 0x3f000000
 #define PERIPH_PHYS_BASE 0x7e000000
 #define DRAM_PHYS_BASE 0xc0000000
 #define MEM_FLAG 0x04
+#define PLLFREQ 500000000.
+#elif (RASPI)==4
+#define PERIPH_VIRT_BASE 0xfe000000
+#define PERIPH_PHYS_BASE 0x7e000000
+#define DRAM_PHYS_BASE 0xc0000000
+#define MEM_FLAG 0x04
+#define PLLFREQ 750000000.
 #else
 #error Unknown Raspberry Pi version (variable RASPI)
 #endif
@@ -185,8 +193,6 @@
 
 #define GPFSEL0            (0x00/4)
 
-#define PLLFREQ            500000000.    // PLLD is running at 500MHz
-
 // The deviation specifies how wide the signal is. Use 25.0 for WBFM
 // (broadcast radio) and about 3.5 for NBFM (walkie-talkie style radio)
 #define DEVIATION        25.0
@@ -392,7 +398,7 @@ int tx(uint32_t carrier_freq, char *audio_file, uint16_t pi, char *ps, char *rt,
     // register.
     //
     // Set the range to 2 bits. PLLD is at 500 MHz, therefore to get 228 kHz
-    // we need a divisor of 500000 / 2 / 228 = 1096.491228
+    // we need a divisor of 500000000 / 2000 / 228 = 1096.491228
     //
     // This is 1096 + 2012*2^-12 theoretically
     //
@@ -403,7 +409,7 @@ int tx(uint32_t carrier_freq, char *audio_file, uint16_t pi, char *ps, char *rt,
     //
     // So we use the 'ppm' parameter to compensate for the oscillator error
 
-    float divider = (500000./(2*228*(1.+ppm/1.e6)));
+    float divider = (PLLFREQ/(2000*228*(1.+ppm/1.e6)));
     uint32_t idivider = (uint32_t) divider;
     uint32_t fdivider = (uint32_t) ((divider - idivider)*pow(2, 12));