samd/machine_spi: Register SerCom objects as root pointers.

Protect SerCom (UART, SPI, I2C) objects from getting freed by the GC when
they go out of scope without being deinitialized.  Otherwise the ISR of a
Sercom may access an invalid data structure.

ports/samd/machine_i2c.c

@@ -69,7 +69,6 @@ typedef struct _machine_i2c_obj_t {
 } machine_i2c_obj_t;
 
 extern Sercom *sercom_instance[];
-extern void *sercom_table[SERCOM_INST_NUM];
 
 STATIC void i2c_send_command(Sercom *i2c, uint8_t command) {
     i2c->I2CM.CTRLB.bit.CMD = command;
@@ -79,7 +78,7 @@ STATIC void i2c_send_command(Sercom *i2c, uint8_t command) {
 
 void common_i2c_irq_handler(int i2c_id) {
     // handle Sercom I2C IRQ
-    machine_i2c_obj_t *self = sercom_table[i2c_id];
+    machine_i2c_obj_t *self = MP_STATE_PORT(sercom_table[i2c_id]);
     // Handle IRQ
     if (self != NULL) {
         Sercom *i2c = self->instance;
@@ -159,7 +158,7 @@ mp_obj_t machine_i2c_make_new(const mp_obj_type_t *type, size_t n_args, size_t n
     if (sda_pad_config.pad_nr != 0 || scl_pad_config.pad_nr != 1) {
         mp_raise_ValueError(MP_ERROR_TEXT("invalid pin for sda or scl"));
     }
-    sercom_table[self->id] = self;
+    MP_STATE_PORT(sercom_table[self->id]) = self;
     self->freq = args[ARG_freq].u_int;
 
     // Configure the Pin mux.

ports/samd/machine_spi.c

@@ -57,11 +57,11 @@ typedef struct _machine_spi_obj_t {
 } machine_spi_obj_t;
 
 extern Sercom *sercom_instance[];
-void *sercom_table[SERCOM_INST_NUM] = {};
+MP_REGISTER_ROOT_POINTER(void *sercom_table[SERCOM_INST_NUM]);
 
 void common_spi_irq_handler(int spi_id) {
     // handle Sercom IRQ RXC
-    machine_spi_obj_t *self = sercom_table[spi_id];
+    machine_spi_obj_t *self = MP_STATE_PORT(sercom_table[spi_id]);
     // Handle IRQ
     if (self != NULL) {
         Sercom *spi = sercom_instance[self->id];
@@ -246,7 +246,7 @@ STATIC mp_obj_t machine_spi_make_new(const mp_obj_type_t *type, size_t n_args, s
     self->sck = 0xff;
 
     self->new = true;
-    sercom_table[spi_id] = self;
+    MP_STATE_PORT(sercom_table[spi_id]) = self;
 
     mp_map_t kw_args;
     mp_map_init_fixed_table(&kw_args, n_kw, args + n_args);
@@ -261,7 +261,7 @@ STATIC void machine_sercom_deinit(mp_obj_base_t *self_in) {
     spi->SPI.INTENCLR.reg = 0xff;
     sercom_enable(spi, 0);
     // clear table entry of spi
-    sercom_table[self->id] = NULL;
+    MP_STATE_PORT(sercom_table[self->id]) = NULL;
 }
 
 void sercom_deinit_all(void) {
@@ -270,7 +270,7 @@ void sercom_deinit_all(void) {
         spi->SPI.INTENCLR.reg = 0xff;
         sercom_register_irq(i, NULL);
         sercom_enable(spi, 0);
-        sercom_table[i] = NULL;
+        MP_STATE_PORT(sercom_table[i]) = NULL;
     }
 }
 

ports/samd/machine_uart.c

@@ -59,7 +59,6 @@ typedef struct _machine_uart_obj_t {
 } machine_uart_obj_t;
 
 Sercom *sercom_instance[] = SERCOM_INSTS;
-extern void *sercom_table[SERCOM_INST_NUM];
 
 STATIC const char *_parity_name[] = {"None", "", "0", "1"};  // Is defined as 0, 2, 3
 
@@ -82,7 +81,7 @@ STATIC void uart_drain_rx_fifo(machine_uart_obj_t *self, Sercom *uart) {
 }
 
 void common_uart_irq_handler(int uart_id) {
-    machine_uart_obj_t *self = sercom_table[uart_id];
+    machine_uart_obj_t *self = MP_STATE_PORT(sercom_table[uart_id]);
     // Handle IRQ
     if (self != NULL) {
         Sercom *uart = sercom_instance[self->id];
@@ -333,7 +332,7 @@ STATIC mp_obj_t machine_uart_make_new(const mp_obj_type_t *type, size_t n_args,
     self->tx = 0xff;
     self->rx = 0xff;
     self->new = true;
-    sercom_table[uart_id] = self;
+    MP_STATE_PORT(sercom_table[uart_id]) = self;
 
     mp_map_t kw_args;
     mp_map_init_fixed_table(&kw_args, n_kw, args + n_args);
@@ -352,7 +351,7 @@ STATIC mp_obj_t machine_uart_deinit(mp_obj_t self_in) {
     // Disable interrupts
     uart->USART.INTENCLR.reg = 0xff;
     // clear table entry of uart
-    sercom_table[self->id] = NULL;
+    MP_STATE_PORT(sercom_table[self->id]) = NULL;
     MP_STATE_PORT(samd_uart_rx_buffer[self->id]) = NULL;
     #if MICROPY_HW_UART_TXBUF
     MP_STATE_PORT(samd_uart_tx_buffer[self->id]) = NULL;