qemu-arm: Rework to run bare-metal on boards with Cortex-M CPUs.

Adds support for 3 Cortex-M boards, selectable via "BOARD" in the Makefile:
- microbit, Cortex-M0 via nRF51822
- netduino2, Cortex-M3 via STM32F205
- mps2-an385, Cortex-M3 via FPGA

netduino2 is the default board because it's supported by older qemu
versions (down to at least 2.5.0).

1 files changed, 78 insertions, 0 deletions

diff --git a/ports/qemu-arm/uart.c b/ports/qemu-arm/uart.c
new file mode 100644
index 000000000..a0ce737c0
--- /dev/null
+++ b/ports/qemu-arm/uart.c
@@ -0,0 +1,78 @@
+#include <stdint.h>
+#include <stddef.h>
+
+#include "uart.h"
+
+#if defined(QEMU_SOC_STM32)
+
+typedef struct _UART_t {
+    volatile uint32_t SR;
+    volatile uint32_t DR;
+} UART_t;
+
+#define UART0 ((UART_t*)(0x40011000))
+
+void uart_init(void) {
+}
+
+void uart_tx_strn(const char *buf, size_t len) {
+    for (size_t i = 0; i < len; ++i) {
+        UART0->DR = buf[i];
+    }
+}
+
+#elif defined(QEMU_SOC_NRF51)
+
+typedef struct _UART_t {
+    volatile uint32_t r0[2];
+    volatile uint32_t STARTTX;  // 0x008
+    volatile uint32_t r1[(0x500 - 0x008) / 4 - 1];
+    volatile uint32_t ENABLE;   // 0x500
+    volatile uint32_t r2[(0x51c - 0x500) / 4 - 1];
+    volatile uint32_t TXD;      // 0x51c
+} UART_t;
+
+#define UART0 ((UART_t*)(0x40002000))
+
+void uart_init(void) {
+    UART0->ENABLE = 4;
+    UART0->STARTTX = 1;
+}
+
+void uart_tx_strn(const char *buf, size_t len) {
+    for (size_t i = 0; i < len; ++i) {
+        UART0->TXD = buf[i];
+    }
+}
+
+#elif defined(QEMU_SOC_MPS2)
+
+#define UART_STATE_TXFULL (1 << 0)
+
+#define UART_CTRL_TX_EN (1 << 0)
+#define UART_CTRL_RX_EN (1 << 1)
+
+typedef struct _UART_t {
+    volatile uint32_t DATA;
+    volatile uint32_t STATE;
+    volatile uint32_t CTRL;
+    volatile uint32_t INTSTATUS;
+    volatile uint32_t BAUDDIV;
+} UART_t;
+
+#define UART0 ((UART_t*)(0x40004000))
+
+void uart_init(void) {
+    UART0->BAUDDIV = 16;
+    UART0->CTRL = UART_CTRL_TX_EN;
+}
+
+void uart_tx_strn(const char *buf, size_t len) {
+    for (size_t i = 0; i < len; ++i) {
+        while (UART0->STATE & UART_STATE_TXFULL) {
+        }
+        UART0->DATA = buf[i];
+    }
+}
+
+#endif