casting pointers

[Stanislav Silnitskiy]

Hello!

I've bumped into the issue with casting...

main.c:
static ble_gap_addr_t addr0;
static uint16_t *p_host0;

int main(void) {
    p_host0 = (void*)&addr0.addr[0];

works fine, but...

beacon.c:
static ble_gap_addr_t addr1;
static uint16_t *p_host1;

void init_beacon(void) {
   p_host1 = (void*)&addr1.addr[0];

hungs in assignment when I call init_beacon() from main()

Where is rake?

[Stanislav Silnitskiy]

It must be memory alignment issue.

[Stanislav Silnitskiy]

definitely it is:

**Cortex-M0 Devices Generic User Guide

Home > The Cortex-M0 Instruction Set > About the instruction descriptions > Address alignment

3.3.4. Address alignment

An aligned access is an operation where a word-aligned address is used for a word, or multiple word access, or where a halfword-aligned address is used for a halfword access. Byte accesses are always aligned. There is no support for unaligned accesses on the Cortex-M0 processor. Any attempt to perform an unaligned memory access operation results in a HardFault exception.**

[Stanislav Silnitskiy]

I tried to avoid editing SDK, but the only plausible solution I see, is to switch places of struct. members and add alignment (not sure, either it is really required):

ble_gap.h:

/**@brief Bluetooth Low Energy address. */
typedef struct
{
  uint8_t addr[BLE_GAP_ADDR_LEN];       /**< 48-bit address, LSB format. */
  uint8_t addr_type;                    /**< See @ref BLE_GAP_ADDR_TYPES. */
} ble_gap_addr_t __attribute__((aligned(16)));

[monpetit]

I have tested in another way.

#pragma anon_unions
typedef struct {
    uint8_t addr_type;                    /**< See @ref BLE_GAP_ADDR_TYPES. */
    union {
        uint8_t addr[BLE_GAP_ADDR_LEN];   /**< 48-bit address, LSB format. */
        __packed struct {
            uint16_t host;
            uint32_t net;
        };
    };
} my_gap_addr_t;


static ble_gap_addr_t addr1 = { 0x00, { 0x01, 0x02, 0x03, 0x04, 0x05, 0x06 } };
static ble_gap_addr_t *p_addr;
static my_gap_addr_t  *p_mddr;

#define show(P) \
    printf("(0x%02x, 0x%02x, 0x%02x, 0x%02x, 0x%02x, 0x%02x)\r\n", \
        P->addr[0], P->addr[1], P->addr[2], P->addr[3], P->addr[4], P->addr[5])

[monpetit]

...

void test_something(void)
{
    p_addr = &addr1;
    p_mddr = (my_gap_addr_t*)&addr1;

    show(p_addr);
    show(p_mddr);
    printf("0x%04x\r\n", p_mddr->host);
    puts("---");
    
    addr1.addr[0] = 0xab;
    addr1.addr[1] = 0xcd;
    show(p_addr);
    show(p_mddr);
    printf("0x%04x\r\n", p_mddr->host);
    puts("---");
    
    const uint8_t buffer[] = { 0xfe, 0xdc, 0xba, 0x98, 0x76, 0x54 };
    memcpy((void*)addr1.addr, (const void*)buffer, sizeof(buffer));
    show(p_addr);
    show(p_mddr);
    printf("0x%04x\r\n", p_mddr->host);
    puts("---");
}

[Stanislav Silnitskiy]

Awesome. although gcc doesn't want this pragma, it just works!