Custom_FIFO is the structure defined in user_define.h. This is also shown in Figure 2-5.

typedef struct {
    uint16_t fifo_in;
    uint16_t fifo_out;
    uint16_t fifo_count;
    Custom_Element *fifo_pointer;
} Custom_FIFO;

gCan2Uart_FIFO and gUart2Can_FIFO are defined in main.c. Please note the usage of SRAM, which is related to C2U_FIFO_SIZE, U2C_FIFO_SIZE and the size for Custom_Element.

/* Variables for C2U_FIFO
 * C2U_FIFO is used to temporarily store message from CAN to UART */
Custom_Element gC2U_FIFO[C2U_FIFO_SIZE];
Custom_FIFO gCan2Uart_FIFO = {0, 0, 0, gC2U_FIFO};

/* Variables for U2C_FIFO
 * U2C_FIFO is used to temporarily store message from UART to CAN */
Custom_Element gU2C_FIFO[U2C_FIFO_SIZE];
Custom_FIFO gUart2Can_FIFO = {0, 0, 0, gU2C_FIFO};