samd21: Initial support for SAMD21 micro-controllers

Add initial support for the Atmel SAMD21 micro-controllers.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

1 files changed, 61 insertions, 0 deletions

diff --git a/src/samd21/serial.c b/src/samd21/serial.c
new file mode 100644
index 00000000..3c321e47
--- /dev/null
+++ b/src/samd21/serial.c
@@ -0,0 +1,61 @@
+// samd21 serial port
+//
+// Copyright (C) 2018  Kevin O'Connor <kevin@koconnor.net>
+//
+// This file may be distributed under the terms of the GNU GPLv3 license.
+
+#include "autoconf.h" // CONFIG_SERIAL_BAUD
+#include "board/serial_irq.h" // serial_rx_data
+#include "internal.h" // enable_pclock
+#include "samd21.h" // SERCOM0
+#include "sched.h" // DECL_INIT
+
+void
+serial_init(void)
+{
+    // Enable serial clock
+    enable_pclock(SERCOM0_GCLK_ID_CORE, PM_APBCMASK_SERCOM0);
+    // Enable pins
+    gpio_peripheral('A', 10, 'C', 0);
+    gpio_peripheral('A', 11, 'C', 0);
+    // Configure serial
+    SercomUsart *su = &SERCOM0->USART;
+    su->CTRLA.reg = 0;
+    uint32_t areg = (SERCOM_USART_CTRLA_MODE_USART_INT_CLK
+                     | SERCOM_USART_CTRLA_DORD
+                     | SERCOM_USART_CTRLA_SAMPR(1)
+                     | SERCOM_USART_CTRLA_TXPO(1)
+                     | SERCOM_USART_CTRLA_RXPO(3));
+    su->CTRLA.reg = areg;
+    su->CTRLB.reg = SERCOM_USART_CTRLB_TXEN | SERCOM_USART_CTRLB_RXEN;
+    uint32_t baud8 = CONFIG_CLOCK_FREQ / (2 * CONFIG_SERIAL_BAUD);
+    su->BAUD.reg = (SERCOM_USART_BAUD_FRAC_BAUD(baud8 / 8)
+                    | SERCOM_USART_BAUD_FRAC_FP(baud8 % 8));
+    NVIC_SetPriority(SERCOM0_IRQn, 0);
+    NVIC_EnableIRQ(SERCOM0_IRQn);
+    su->INTENSET.reg = SERCOM_USART_INTENSET_RXC;
+    su->CTRLA.reg = areg | SERCOM_USART_CTRLA_ENABLE;
+}
+DECL_INIT(serial_init);
+
+void __visible
+SERCOM0_Handler(void)
+{
+    uint32_t status = SERCOM0->USART.INTFLAG.reg;
+    if (status & SERCOM_USART_INTFLAG_RXC)
+        serial_rx_byte(SERCOM0->USART.DATA.reg);
+    if (status & SERCOM_USART_INTFLAG_DRE) {
+        uint8_t data;
+        int ret = serial_get_tx_byte(&data);
+        if (ret)
+            SERCOM0->USART.INTENCLR.reg = SERCOM_USART_INTENSET_DRE;
+        else
+            SERCOM0->USART.DATA.reg = data;
+    }
+}
+
+void
+serial_enable_tx_irq(void)
+{
+    SERCOM0->USART.INTENSET.reg = SERCOM_USART_INTENSET_DRE;
+}