From 6d0a60881c08b7bf76f7c0cb11af4ef0ebe6b7f8 Mon Sep 17 00:00:00 2001
From: Matte23 <matteo.schiff23@gmail.com>
Date: Sun, 3 Nov 2024 12:04:40 +0100
Subject: [PATCH] Add example USART driver

---
 Makefile          |  4 ++--
 libc/library.c    |  8 ++-----
 os/delay.c        | 18 +++++++++++++++
 os/delay.h        |  2 ++
 os/driver/usart.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++
 os/driver/usart.h | 12 ++++++++++
 6 files changed, 93 insertions(+), 8 deletions(-)
 create mode 100644 os/delay.c
 create mode 100644 os/delay.h
 create mode 100644 os/driver/usart.c
 create mode 100644 os/driver/usart.h

diff --git a/Makefile b/Makefile
index c5e0352..4a9ef52 100644
--- a/Makefile
+++ b/Makefile
@@ -5,7 +5,7 @@ CPU = -mcpu=cortex-m4
 THUMB = -mthumb
 
 LDFLAGS = -T linker.ld
-CFLAGS = $(CPU) $(THUMB) -I libc/
+CFLAGS = $(CPU) $(THUMB) -I libc/ -I ./
 
 QEMU = qemu-system-arm
 BOARD = netduino2
@@ -13,7 +13,7 @@ BOARD = netduino2
 # Output file
 TARGET = main.elf
 # Source files
-SRCS = os/main.c os/process.c os/scheduler.c os/alloc.c libc/library.c tasks/tasks.c
+SRCS = os/main.c os/process.c os/scheduler.c os/alloc.c os/delay.c os/driver/usart.c libc/library.c tasks/tasks.c
 # Object files
 OBJS = $(SRCS:.c=.o)
 
diff --git a/libc/library.c b/libc/library.c
index c37f1ee..650534a 100644
--- a/libc/library.c
+++ b/libc/library.c
@@ -1,10 +1,6 @@
 #include "library.h"
-
-volatile unsigned int *const USART1_PTR = (unsigned int *)0x40011004;
+#include "os/driver/usart.h"
 
 void puts(const char *s) {
-    while(*s != '\0') { /* Loop until end of string */
-        *USART1_PTR= (unsigned int)(*s); /* Transmit char */
-        s++; /* Next char */
-    }
+    usart_tx_write_string(s);
 }
diff --git a/os/delay.c b/os/delay.c
new file mode 100644
index 0000000..b0a86a3
--- /dev/null
+++ b/os/delay.c
@@ -0,0 +1,18 @@
+#define CLOCK_FREQUENCY 120000
+
+unsigned int ms_to_ticks(unsigned int ms) {
+    return ms * (CLOCK_FREQUENCY/3);
+}
+
+void delay_routine(unsigned int delay_counter) {
+    asm("mov r1, %[input]\n"
+    "loop_2:\n"
+    "subs r1, #1\n"
+    "cmp r1, #0\n"
+    "bne loop_2\n"
+    : [input] "=r" (delay_counter));
+}
+
+void delay_ms(unsigned int seconds) {
+    delay_routine(ms_to_ticks(seconds));
+}
diff --git a/os/delay.h b/os/delay.h
new file mode 100644
index 0000000..f7d0b87
--- /dev/null
+++ b/os/delay.h
@@ -0,0 +1,2 @@
+void delay_routine(unsigned int delay_counter);
+void delay_ms(unsigned int ms);
diff --git a/os/driver/usart.c b/os/driver/usart.c
new file mode 100644
index 0000000..4b6e662
--- /dev/null
+++ b/os/driver/usart.c
@@ -0,0 +1,57 @@
+#include "usart.h"
+#include "os/delay.h"
+#include <stddef.h>
+#include <stdint.h>
+#define USART_SR_TXE (1 << 7)
+
+typedef struct uart_s {
+    uint32_t USART_SR;
+    uint32_t USART_DR;
+    uint32_t USART_BRR;
+    uint32_t USART_CR1;
+    uint32_t USART_CR2;
+    uint32_t USART_CR3;
+    uint32_t USART_GTPR;
+} uart_c;
+
+volatile uart_c *const USART1 = (uart_c *)0x40011000;
+
+static uint32_t usart_tx_ready(void) {
+    return (USART1->USART_SR & USART_SR_TXE) >> 7;
+}
+
+uint32_t usart_tx_write(const uint8_t *data_bytes, uint32_t n_bytes) {
+    if (data_bytes == NULL) return USART_TX_ERROR;
+
+    for (int i = 0; i < n_bytes; i++) {
+        unsigned int timeout = TIMEOUT;
+        while (!usart_tx_ready()) {
+            delay_ms(1);
+            timeout--;
+            if (timeout == 0) return USART_TX_BUSY;
+        }
+
+        USART1->USART_DR = *data_bytes;
+
+        data_bytes++;
+    }
+    return USART_TX_COMPLETE;
+}
+
+uint32_t usart_tx_write_string(const uint8_t *data_bytes) {
+    if (data_bytes == NULL) return USART_TX_ERROR;
+
+    while (*data_bytes != '\0') {
+        unsigned int timeout = TIMEOUT;
+        while (!usart_tx_ready()) {
+            delay_ms(1);
+            timeout--;
+            if (timeout == 0) return USART_TX_BUSY;
+        }
+
+        USART1->USART_DR = *data_bytes;
+
+        data_bytes++;
+    }
+    return USART_TX_COMPLETE;
+}
diff --git a/os/driver/usart.h b/os/driver/usart.h
new file mode 100644
index 0000000..99cfbd5
--- /dev/null
+++ b/os/driver/usart.h
@@ -0,0 +1,12 @@
+#include <stdint.h>
+#define TIMEOUT 1000
+
+enum UartErrorCode {
+    USART_TX_ERROR,
+    USART_TX_BUSY,
+    USART_TX_COMPLETE
+};
+
+static uint32_t usart_tx_ready(void);
+uint32_t usart_tx_write(const uint8_t *data_bytes, uint32_t n_bytes);
+uint32_t usart_tx_write_string(const uint8_t *data_bytes);
\ No newline at end of file