diff --git a/litex/soc/cores/cpu/eos_s3/boot-helper.c b/litex/soc/cores/cpu/eos_s3/boot-helper.c
new file mode 100644
index 000000000..9a2695e2f
--- /dev/null
+++ b/litex/soc/cores/cpu/eos_s3/boot-helper.c
@@ -0,0 +1,5 @@
+void boot_helper(unsigned long r1, unsigned long r2, unsigned long r3, unsigned long addr);
+
+void boot_helper(unsigned long r1, unsigned long r2, unsigned long r3, unsigned long addr) {
+    goto *addr;
+}
\ No newline at end of file
diff --git a/litex/soc/cores/cpu/eos_s3/core.py b/litex/soc/cores/cpu/eos_s3/core.py
index 8552939d4..b78d9c8e1 100644
--- a/litex/soc/cores/cpu/eos_s3/core.py
+++ b/litex/soc/cores/cpu/eos_s3/core.py
@@ -24,18 +24,24 @@ class EOS_S3(CPU):
     human_name           = "EOS S3"
     data_width           = 32
     endianness           = "little"
-    reset_address        = 0x00000000
-    gcc_triple           = "gcc-arm-none-eabi"
+    reset_address        = 0x0000_0000
+    gcc_triple           = "arm-none-eabi"
+    gcc_flags            = "-mcpu=cortex-m4 -mthumb -mfloat-abi=hard -mfpu=fpv4-sp-d16"
     linker_output_format = "elf32-littlearm"
     nop                  = "nop"
-    io_regions           = {0x00000000: 0x100000000} # Origin, Length.
+    io_regions           = {0x4000_0000: 0xc000_0000}  # Origin, Length.
 
     # Memory Mapping.
     @property
     def mem_map(self):
-        return {"csr": 0x00000000}
+        return {
+            "rom":  0x0000_0000,
+            "sram": 0x2000_0000,
+            "csr":  0x4002_0000
+        }
 
-    def __init__(self, platform, variant):
+    def __init__(self, platform, variant, *args, **kwargs):
+        super().__init__(*args, **kwargs)
         self.platform       = platform
         self.reset          = Signal()
         self.interrupt      = Signal(4)
diff --git a/litex/soc/cores/cpu/eos_s3/crt0.c b/litex/soc/cores/cpu/eos_s3/crt0.c
new file mode 100644
index 000000000..44134ee07
--- /dev/null
+++ b/litex/soc/cores/cpu/eos_s3/crt0.c
@@ -0,0 +1,35 @@
+#include <stdint.h>
+
+extern uint32_t _fdata_rom, _fdata, _edata, _fbss, _ebss;
+
+void SystemInit(void);
+void Reset_Handler(void);
+void _start(void);
+
+void _start(void) {
+  Reset_Handler();
+}
+
+void Reset_Handler(void) {
+  uint32_t *y = &_fdata_rom;
+  for (uint32_t *x = &_fdata; x < &_edata; x ++)
+    *x = *y ++;
+
+  for (uint32_t *x = &_fbss; x < &_ebss; x ++)
+    *x = 0;
+
+#ifndef __NO_SYSTEM_INIT
+  SystemInit();
+#endif
+
+  // just in case - for now EOS CPU support relies on QORC SDK
+  // and main() is launched inside SystemInit() as FreeRTOS task
+  // so this call is not reached
+  __asm__("bl main");
+}
+
+__attribute__((weak)) uint32_t __semihost_call(uint32_t r0, uint32_t r1);
+
+__attribute__((weak)) uint32_t __semihost_call(uint32_t r0, uint32_t r1) {
+  return 0;
+}
diff --git a/litex/soc/cores/cpu/eos_s3/irq.h b/litex/soc/cores/cpu/eos_s3/irq.h
new file mode 100644
index 000000000..4c87950ef
--- /dev/null
+++ b/litex/soc/cores/cpu/eos_s3/irq.h
@@ -0,0 +1,37 @@
+#ifndef __IRQ_H
+#define __IRQ_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+static inline unsigned int irq_getie(void)
+{
+	return 0; /* FIXME */
+}
+
+static inline void irq_setie(unsigned int ie)
+{
+	/* FIXME */
+}
+
+static inline unsigned int irq_getmask(void)
+{
+	return 0; /* FIXME */
+}
+
+static inline void irq_setmask(unsigned int mask)
+{
+	/* FIXME */
+}
+
+static inline unsigned int irq_pending(void)
+{
+	return 0; /* FIXME */
+}
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __IRQ_H */
diff --git a/litex/soc/cores/cpu/eos_s3/system.h b/litex/soc/cores/cpu/eos_s3/system.h
new file mode 100644
index 000000000..a0d777a85
--- /dev/null
+++ b/litex/soc/cores/cpu/eos_s3/system.h
@@ -0,0 +1,56 @@
+#ifndef __SYSTEM_H
+#define __SYSTEM_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+#include <stdint.h>
+
+__attribute__((unused)) static void flush_cpu_icache(void){};
+__attribute__((unused)) static void flush_cpu_dcache(void){};
+void flush_l2_cache(void);
+
+void busy_wait(unsigned int ms);
+void busy_wait_us(unsigned int us);
+
+#define CSR_UART_BASE
+#define UART_POLLING
+#define UART_ID_HW 1 // hard UART on the S3
+#define UART_ID UART_ID_HW
+
+void uart_tx(int uartid, int c);
+int uart_rx(int uartid);
+int uart_rx_available(int uartid);
+int uart_tx_is_fifo_full(int uart_id);
+
+static inline void uart_rxtx_write(char c) {
+    uart_tx(UART_ID, c);
+}
+
+static inline uint8_t uart_rxtx_read(void) {
+    return uart_rx(UART_ID);
+}
+
+static inline uint8_t uart_txfull_read(void) {
+    return uart_tx_is_fifo_full(UART_ID);
+}
+
+static inline uint8_t uart_rxempty_read(void) {
+    return uart_rx_available(UART_ID);
+}
+
+static inline void uart_ev_pending_write(uint8_t x) {}
+
+static inline uint8_t uart_ev_pending_read(void) {
+    return 0;
+}
+
+static inline void uart_ev_enable_write(uint8_t x) {}
+
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __SYSTEM_H */
diff --git a/litex/soc/integration/builder.py b/litex/soc/integration/builder.py
index 653f85f0a..50e08dbed 100644
--- a/litex/soc/integration/builder.py
+++ b/litex/soc/integration/builder.py
@@ -281,7 +281,7 @@ class Builder:
         self.soc.platform.output_dir = self.output_dir
 
         # Check if BIOS is used and add software package if so.
-        with_bios = self.soc.cpu_type not in [None, "eos-s3", 'gowin_emcu']
+        with_bios = self.soc.cpu_type not in [None, 'gowin_emcu']
         if with_bios:
             self.add_software_package("bios")
 
diff --git a/litex/soc/integration/soc.py b/litex/soc/integration/soc.py
index f5f2540a5..72630b284 100644
--- a/litex/soc/integration/soc.py
+++ b/litex/soc/integration/soc.py
@@ -1094,7 +1094,7 @@ class SoC(Module):
             self.add_constant(name + "_" + constant.name, constant.value.value)
 
         # SoC CPU Check ----------------------------------------------------------------------------
-        if not isinstance(self.cpu, (cpu.CPUNone, cpu.EOS_S3)):
+        if not isinstance(self.cpu, cpu.CPUNone):
             cpu_reset_address_valid = False
             for name, container in self.bus.regions.items():
                 if self.bus.check_region_is_in(