DAPLink/core/SWD_host/SWD_host.c

/**
 * @file    SWDd_host.c
 * @brief   Host driver for accessing the DAP
 */
#include "swd_host.h"

#include "DAP_config.h"
#include "DAP.h"
#include "debug_cm.h"

uint32_t Flash_Page_Size = 4096;

extern uint32_t Flash_Page_Size;


#define NVIC_Addr    (0xe000e000)
#define DBG_Addr     (0xe000edf0)

// AP CSW register, base value
#define CSW_VALUE (CSW_RESERVED | CSW_MSTRDBG | CSW_HPROT | CSW_DBGSTAT | CSW_SADDRINC)

// SWD register access
#define SWD_REG_AP        (1)
#define SWD_REG_DP        (0)
#define SWD_REG_R         (1<<1)
#define SWD_REG_W         (0<<1)
#define SWD_REG_ADR(a)    (a & 0x0c)

#define DCRDR 0xE000EDF8
#define DCRSR 0xE000EDF4
#define DHCSR 0xE000EDF0
#define REGWnR (1 << 16)

#define MAX_SWD_RETRY 10
#define MAX_TIMEOUT   1000000  // Timeout for syscalls on target


typedef struct {
    uint32_t select;
    uint32_t csw;
} DAP_STATE;

typedef struct {
    uint32_t r[16];
    uint32_t xpsr;
} DEBUG_STATE;

static DAP_STATE dap_state;

static uint8_t swd_read_core_register(uint32_t n, uint32_t *val);
static uint8_t swd_write_core_register(uint32_t n, uint32_t val);


void delaymS(uint32_t ms)
{
	uint32_t cnt = SystemCoreClock/4/1000 * ms;
	
	for(uint32_t i = 0; i < cnt; i++)  __NOP();
}


static void int2array(uint8_t *res, uint32_t data, uint8_t len)
{
    uint8_t i = 0;

    for(i = 0; i < len; i++) {
        res[i] = (data >> 8 * i) & 0xFF;
    }
}

static uint8_t swd_transfer_retry(uint32_t req, uint32_t *data)
{
    uint8_t i, ack;

    for (i = 0; i < MAX_SWD_RETRY; i++) {
        ack = SWD_Transfer(req, data);

        if (ack != DAP_TRANSFER_WAIT) {
            return ack;
        }
    }

    return ack;
}


uint8_t swd_init(void)
{
    DAP_Setup();
    PORT_SWD_SETUP();
	
    return 1;
}

uint8_t swd_off(void)
{
    PORT_OFF();
	
    return 1;
}

// Read debug port register.
uint8_t swd_read_dp(uint8_t adr, uint32_t *val)
{
    uint32_t tmp_in;
    uint8_t tmp_out[4];
    uint8_t ack;
    uint32_t tmp;
	
    tmp_in = SWD_REG_DP | SWD_REG_R | SWD_REG_ADR(adr);
    ack = swd_transfer_retry(tmp_in, (uint32_t *)tmp_out);
	
    *val = 0;
    tmp = tmp_out[3];
    *val |= (tmp << 24);
    tmp = tmp_out[2];
    *val |= (tmp << 16);
    tmp = tmp_out[1];
    *val |= (tmp << 8);
    tmp = tmp_out[0];
    *val |= (tmp << 0);
	
    return (ack == 0x01);
}

// Write debug port register
uint8_t swd_write_dp(uint8_t adr, uint32_t val)
{
    uint32_t req;
    uint8_t data[4];
    uint8_t ack;

    switch (adr) {
        case DP_SELECT:
            if (dap_state.select == val) {
                return 1;
            }

            dap_state.select = val;
            break;

        default:
            break;
    }

    req = SWD_REG_DP | SWD_REG_W | SWD_REG_ADR(adr);
    int2array(data, val, 4);
    ack = swd_transfer_retry(req, (uint32_t *)data);
	
    return (ack == 0x01);
}

// Read access port register.
uint8_t swd_read_ap(uint32_t adr, uint32_t *val)
{
    uint8_t tmp_in, ack;
    uint8_t tmp_out[4];
    uint32_t tmp;
    uint32_t apsel = adr & 0xff000000;
    uint32_t bank_sel = adr & APBANKSEL;

    if (!swd_write_dp(DP_SELECT, apsel | bank_sel)) {
        return 0;
    }

    tmp_in = SWD_REG_AP | SWD_REG_R | SWD_REG_ADR(adr);
    // first dummy read
    swd_transfer_retry(tmp_in, (uint32_t *)tmp_out);
    ack = swd_transfer_retry(tmp_in, (uint32_t *)tmp_out);
	
    *val = 0;
    tmp = tmp_out[3];
    *val |= (tmp << 24);
    tmp = tmp_out[2];
    *val |= (tmp << 16);
    tmp = tmp_out[1];
    *val |= (tmp << 8);
    tmp = tmp_out[0];
    *val |= (tmp << 0);
	
    return (ack == 0x01);
}

// Write access port register
uint8_t swd_write_ap(uint32_t adr, uint32_t val)
{
    uint8_t data[4];
    uint8_t req, ack;
    uint32_t apsel = adr & 0xff000000;
    uint32_t bank_sel = adr & APBANKSEL;

    if (!swd_write_dp(DP_SELECT, apsel | bank_sel)) {
        return 0;
    }

    switch (adr) {
        case AP_CSW:
            if (dap_state.csw == val) {
                return 1;
            }

            dap_state.csw = val;
            break;

        default:
            break;
    }

    req = SWD_REG_AP | SWD_REG_W | SWD_REG_ADR(adr);
    int2array(data, val, 4);

    if (swd_transfer_retry(req, (uint32_t *)data) != 0x01) {
        return 0;
    }

    req = SWD_REG_DP | SWD_REG_R | SWD_REG_ADR(DP_RDBUFF);
    ack = swd_transfer_retry(req, NULL);
	
    return (ack == 0x01);
}


// Write 32-bit word aligned values to target memory using address auto-increment.
// size is in bytes.
static uint8_t swd_write_block(uint32_t address, uint8_t *data, uint32_t size)
{
    uint8_t tmp_in[4], req;
    uint32_t size_in_words;
    uint32_t i, ack;

    if (size == 0) {
        return 0;
    }

    size_in_words = size / 4;

    // CSW register
    if (!swd_write_ap(AP_CSW, CSW_VALUE | CSW_SIZE32)) {
        return 0;
    }

    // TAR write
    req = SWD_REG_AP | SWD_REG_W | (1 << 2);
    int2array(tmp_in, address, 4);

    if (swd_transfer_retry(req, (uint32_t *)tmp_in) != 0x01) {
        return 0;
    }

    // DRW write
    req = SWD_REG_AP | SWD_REG_W | (3 << 2);

    for (i = 0; i < size_in_words; i++) {
        if (swd_transfer_retry(req, (uint32_t *)data) != 0x01) {
            return 0;
        }

        data += 4;
    }

    // dummy read
    req = SWD_REG_DP | SWD_REG_R | SWD_REG_ADR(DP_RDBUFF);
    ack = swd_transfer_retry(req, NULL);
    return (ack == 0x01);
}

// Read 32-bit word aligned values from target memory using address auto-increment.
// size is in bytes.
static uint8_t swd_read_block(uint32_t address, uint8_t *data, uint32_t size)
{
    uint8_t tmp_in[4], req, ack;
    uint32_t size_in_words;
    uint32_t i;

    if (size == 0) {
        return 0;
    }

    size_in_words = size / 4;

    if (!swd_write_ap(AP_CSW, CSW_VALUE | CSW_SIZE32)) {
        return 0;
    }

    // TAR write
    req = SWD_REG_AP | SWD_REG_W | AP_TAR;
    int2array(tmp_in, address, 4);

    if (swd_transfer_retry(req, (uint32_t *)tmp_in) != DAP_TRANSFER_OK) {
        return 0;
    }

    // read data
    req = SWD_REG_AP | SWD_REG_R | AP_DRW;

    // initiate first read, data comes back in next read
    if (swd_transfer_retry(req, NULL) != 0x01) {
        return 0;
    }

    for (i = 0; i < (size_in_words - 1); i++) {
        if (swd_transfer_retry(req, (uint32_t *)data) != DAP_TRANSFER_OK) {
            return 0;
        }

        data += 4;
    }

    // read last word
    req = SWD_REG_DP | SWD_REG_R | SWD_REG_ADR(DP_RDBUFF);
    ack = swd_transfer_retry(req, (uint32_t *)data);
    return (ack == 0x01);
}

// Read target memory.
static uint8_t swd_read_data(uint32_t addr, uint32_t *val)
{
    uint8_t tmp_in[4];
    uint8_t tmp_out[4];
    uint8_t req, ack;
    uint32_t tmp;
    // put addr in TAR register
    int2array(tmp_in, addr, 4);
    req = SWD_REG_AP | SWD_REG_W | (1 << 2);

    if (swd_transfer_retry(req, (uint32_t *)tmp_in) != 0x01) {
        return 0;
    }

    // read data
    req = SWD_REG_AP | SWD_REG_R | (3 << 2);

    if (swd_transfer_retry(req, (uint32_t *)tmp_out) != 0x01) {
        return 0;
    }

    // dummy read
    req = SWD_REG_DP | SWD_REG_R | SWD_REG_ADR(DP_RDBUFF);
    ack = swd_transfer_retry(req, (uint32_t *)tmp_out);
    *val = 0;
    tmp = tmp_out[3];
    *val |= (tmp << 24);
    tmp = tmp_out[2];
    *val |= (tmp << 16);
    tmp = tmp_out[1];
    *val |= (tmp << 8);
    tmp = tmp_out[0];
    *val |= (tmp << 0);
    return (ack == 0x01);
}

// Write target memory.
static uint8_t swd_write_data(uint32_t address, uint32_t data)
{
    uint8_t tmp_in[4];
    uint8_t req, ack;
    // put addr in TAR register
    int2array(tmp_in, address, 4);
    req = SWD_REG_AP | SWD_REG_W | (1 << 2);

    if (swd_transfer_retry(req, (uint32_t *)tmp_in) != 0x01) {
        return 0;
    }

    // write data
    int2array(tmp_in, data, 4);
    req = SWD_REG_AP | SWD_REG_W | (3 << 2);

    if (swd_transfer_retry(req, (uint32_t *)tmp_in) != 0x01) {
        return 0;
    }

    // dummy read
    req = SWD_REG_DP | SWD_REG_R | SWD_REG_ADR(DP_RDBUFF);
    ack = swd_transfer_retry(req, NULL);
    return (ack == 0x01) ? 1 : 0;
}

// Read 32-bit word from target memory.
/* static */ uint8_t swd_read_word(uint32_t addr, uint32_t *val)
{
    if (!swd_write_ap(AP_CSW, CSW_VALUE | CSW_SIZE32)) {
        return 0;
    }

    if (!swd_read_data(addr, val)) {
        return 0;
    }

    return 1;
}

// Write 32-bit word to target memory.
/* static */ uint8_t swd_write_word(uint32_t addr, uint32_t val)
{
    if (!swd_write_ap(AP_CSW, CSW_VALUE | CSW_SIZE32)) {
        return 0;
    }

    if (!swd_write_data(addr, val)) {
        return 0;
    }

    return 1;
}

// Read 8-bit byte from target memory.
static uint8_t swd_read_byte(uint32_t addr, uint8_t *val)
{
    uint32_t tmp;

    if (!swd_write_ap(AP_CSW, CSW_VALUE | CSW_SIZE8)) {
        return 0;
    }

    if (!swd_read_data(addr, &tmp)) {
        return 0;
    }

    *val = (uint8_t)(tmp >> ((addr & 0x03) << 3));
    return 1;
}

// Write 8-bit byte to target memory.
static uint8_t swd_write_byte(uint32_t addr, uint8_t val)
{
    uint32_t tmp;

    if (!swd_write_ap(AP_CSW, CSW_VALUE | CSW_SIZE8)) {
        return 0;
    }

    tmp = val << ((addr & 0x03) << 3);

    if (!swd_write_data(addr, tmp)) {
        return 0;
    }

    return 1;
}

// Read unaligned data from target memory.
// size is in bytes.
uint8_t swd_read_memory(uint32_t address, uint8_t *data, uint32_t size)
{
    uint32_t n;

    // Read bytes until word aligned
    while ((size > 0) && (address & 0x3)) {
        if (!swd_read_byte(address, data)) {
            return 0;
        }

        address++;
        data++;
        size--;
    }

    // Read word aligned blocks
    while (size > 3) {
        // Limit to auto increment page size
        n = Flash_Page_Size - (address & (Flash_Page_Size - 1));

        if (size < n) {
            n = size & 0xFFFFFFFC; // Only count complete words remaining
        }

        if (!swd_read_block(address, data, n)) {
            return 0;
        }

        address += n;
        data += n;
        size -= n;
    }

    // Read remaining bytes
    while (size > 0) {
        if (!swd_read_byte(address, data)) {
            return 0;
        }

        address++;
        data++;
        size--;
    }

    return 1;
}

// Write unaligned data to target memory.
// size is in bytes.
uint8_t swd_write_memory(uint32_t address, uint8_t *data, uint32_t size)
{
    uint32_t n = 0;

    // Write bytes until word aligned
    while ((size > 0) && (address & 0x3)) {
        if (!swd_write_byte(address, *data)) {
            return 0;
        }

        address++;
        data++;
        size--;
    }

    // Write word aligned blocks
    while (size > 3) {
        // Limit to auto increment page size
        n = Flash_Page_Size - (address & (Flash_Page_Size - 1));

        if (size < n) {
            n = size & 0xFFFFFFFC; // Only count complete words remaining
        }

        if (!swd_write_block(address, data, n)) {
            return 0;
        }

        address += n;
        data += n;
        size -= n;
    }

    // Write remaining bytes
    while (size > 0) {
        if (!swd_write_byte(address, *data)) {
            return 0;
        }

        address++;
        data++;
        size--;
    }

    return 1;
}

// Execute system call.
static uint8_t swd_write_debug_state(DEBUG_STATE *state)
{
    uint32_t i, status;

    if (!swd_write_dp(DP_SELECT, 0)) {
        return 0;
    }

    // R0, R1, R2, R3
    for (i = 0; i < 4; i++) {
        if (!swd_write_core_register(i, state->r[i])) {
            return 0;
        }
    }

    // R9
    if (!swd_write_core_register(9, state->r[9])) {
        return 0;
    }

    // R13, R14, R15
    for (i = 13; i < 16; i++) {
        if (!swd_write_core_register(i, state->r[i])) {
            return 0;
        }
    }

    // xPSR
    if (!swd_write_core_register(16, state->xpsr)) {
        return 0;
    }

    if (!swd_write_word(DBG_HCSR, DBGKEY | C_DEBUGEN)) {
        return 0;
    }

    // check status
    if (!swd_read_dp(DP_CTRL_STAT, &status)) {
        return 0;
    }

    if (status & (STICKYERR | WDATAERR)) {
        return 0;
    }

    return 1;
}

static uint8_t swd_read_core_register(uint32_t n, uint32_t *val)
{
    int i = 0, timeout = 100;

    if (!swd_write_word(DCRSR, n)) {
        return 0;
    }

    // wait for S_REGRDY
    for (i = 0; i < timeout; i++) {
        if (!swd_read_word(DHCSR, val)) {
            return 0;
        }

        if (*val & S_REGRDY) {
            break;
        }
    }

    if (i == timeout) {
        return 0;
    }

    if (!swd_read_word(DCRDR, val)) {
        return 0;
    }

    return 1;
}

static uint8_t swd_write_core_register(uint32_t n, uint32_t val)
{
    int i = 0, timeout = 100;

    if (!swd_write_word(DCRDR, val)) {
        return 0;
    }

    if (!swd_write_word(DCRSR, n | REGWnR)) {
        return 0;
    }

    // wait for S_REGRDY
    for (i = 0; i < timeout; i++) {
        if (!swd_read_word(DHCSR, &val)) {
            return 0;
        }

        if (val & S_REGRDY) {
            return 1;
        }
    }

    return 0;
}

static uint8_t swd_wait_until_halted(void)
{
    // Wait for target to stop
    uint32_t val, i, timeout = MAX_TIMEOUT;

    for (i = 0; i < timeout; i++) {
        if (!swd_read_word(DBG_HCSR, &val)) {
            return 0;
        }

        if (val & S_HALT) {
            return 1;
        }
    }

    return 0;
}

uint8_t swd_flash_syscall_exec(const program_syscall_t *sysCallParam, uint32_t entry, uint32_t arg1, uint32_t arg2, uint32_t arg3, uint32_t arg4)
{
    DEBUG_STATE state = {{0}, 0};
    // Call flash algorithm function on target and wait for result.
    state.r[0]     = arg1;                   // R0: Argument 1
    state.r[1]     = arg2;                   // R1: Argument 2
    state.r[2]     = arg3;                   // R2: Argument 3
    state.r[3]     = arg4;                   // R3: Argument 4
    state.r[9]     = sysCallParam->static_base;    // SB: Static Base
    state.r[13]    = sysCallParam->stack_pointer;  // SP: Stack Pointer
    state.r[14]    = sysCallParam->breakpoint;     // LR: Exit Point
    state.r[15]    = entry;                        // PC: Entry Point
    state.xpsr     = 0x01000000;          // xPSR: T = 1, ISR = 0

    if (!swd_write_debug_state(&state)) {
        return 0;
    }

    if (!swd_wait_until_halted()) {
        return 0;
    }

    if (!swd_read_core_register(0, &state.r[0])) {
        return 0;
    }

    // Flash functions return 0 if successful.
    if (state.r[0] != 0) {
        return 0;
    }

    return 1;
}

// SWD Reset
static uint8_t swd_reset(void)
{
    uint8_t tmp_in[8];
    uint8_t i = 0;

    for (i = 0; i < 8; i++) {
        tmp_in[i] = 0xff;
    }

    SWJ_Sequence(51, tmp_in);
    return 1;
}

// SWD Switch
static uint8_t swd_switch(uint16_t val)
{
    uint8_t tmp_in[2];
    tmp_in[0] = val & 0xff;
    tmp_in[1] = (val >> 8) & 0xff;
    SWJ_Sequence(16, tmp_in);
    return 1;
}

// SWD Read ID
static uint8_t swd_read_idcode(uint32_t *id)
{
    uint8_t tmp_in[1];
    uint8_t tmp_out[4];
    tmp_in[0] = 0x00;
    SWJ_Sequence(8, tmp_in);

    if (swd_read_dp(0, (uint32_t *)tmp_out) != 0x01) {
        return 0;
    }

    *id = (tmp_out[3] << 24) | (tmp_out[2] << 16) | (tmp_out[1] << 8) | tmp_out[0];
    return 1;
}


static uint8_t JTAG2SWD()
{
    uint32_t tmp = 0;

    if (!swd_reset()) {
        return 0;
    }

    if (!swd_switch(0xE79E)) {
        return 0;
    }

    if (!swd_reset()) {
        return 0;
    }

    if (!swd_read_idcode(&tmp)) {
        return 0;
    }

    return 1;
}

uint8_t swd_init_debug(void)
{
    uint32_t tmp = 0;
    int i = 0;
    int timeout = 100;
    // init dap state with fake values
    dap_state.select = 0xffffffff;
    dap_state.csw = 0xffffffff;
    swd_init();
	
    // call a target dependant function
    // this function can do several stuff before really initing the debug
    //target_before_init_debug();

    if (!JTAG2SWD()) {
        return 0;
    }

    if (!swd_write_dp(DP_ABORT, STKCMPCLR | STKERRCLR | WDERRCLR | ORUNERRCLR)) {
        return 0;
    }

    // Ensure CTRL/STAT register selected in DPBANKSEL
    if (!swd_write_dp(DP_SELECT, 0)) {
        return 0;
    }

    // Power up
    if (!swd_write_dp(DP_CTRL_STAT, CSYSPWRUPREQ | CDBGPWRUPREQ)) {
        return 0;
    }

    for (i = 0; i < timeout; i++) {
        if (!swd_read_dp(DP_CTRL_STAT, &tmp)) {
            return 0;
        }
        if ((tmp & (CDBGPWRUPACK | CSYSPWRUPACK)) == (CDBGPWRUPACK | CSYSPWRUPACK)) {
            // Break from loop if powerup is complete
            break;
        }
    }
    if (i == timeout) {
        // Unable to powerup DP
        return 0;
    }

    if (!swd_write_dp(DP_CTRL_STAT, CSYSPWRUPREQ | CDBGPWRUPREQ | TRNNORMAL | MASKLANE)) {
        return 0;
    }

    // call a target dependant function:
    // some target can enter in a lock state, this function can unlock these targets
    //target_unlock_sequence();

    if (!swd_write_dp(DP_SELECT, 0)) {
        return 0;
    }

    return 1;
}
/*
__attribute__((weak)) void swd_set_target_reset(uint8_t asserted)
{
    (asserted) ? PIN_nRESET_OUT(0) : PIN_nRESET_OUT(1);
}
*/
void swd_set_target_reset(uint8_t asserted)
{
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    if(asserted == 0)
	{
		swd_write_word((uint32_t)&SCB->AIRCR, ((0x5FA << SCB_AIRCR_VECTKEY_Pos) |(SCB->AIRCR & SCB_AIRCR_PRIGROUP_Msk) | SCB_AIRCR_SYSRESETREQ_Msk));
	}
}

uint8_t swd_set_target_state_hw(TARGET_RESET_STATE state)
{
    uint32_t val;
    int8_t ap_retries = 2;
    /* Calling swd_init prior to entering RUN state causes operations to fail. */
    if (state != RUN) {
        swd_init();
    }

    switch (state) {
        case RESET_HOLD:
            swd_set_target_reset(1);
            break;

        case RESET_RUN:
            swd_set_target_reset(1);
            delaymS(20);
            swd_set_target_reset(0);
            delaymS(20);
            swd_off();
            break;

        case RESET_PROGRAM:
            if (!swd_init_debug()) {
                return 0;
            }

            // Enable debug
            while(swd_write_word(DBG_HCSR, DBGKEY | C_DEBUGEN) == 0) {
                if( --ap_retries <=0 )
                    return 0;
                // Target is in invalid state?
                swd_set_target_reset(1);
                delaymS(20);
                swd_set_target_reset(0);
                delaymS(20);
            }

            // Enable halt on reset
            if (!swd_write_word(DBG_EMCR, VC_CORERESET)) {
                return 0;
            }

            // Reset again
            swd_set_target_reset(1);
            delaymS(20);
            swd_set_target_reset(0);
            delaymS(20);

            do {
                if (!swd_read_word(DBG_HCSR, &val)) {
                    return 0;
                }
            } while ((val & S_HALT) == 0);

            // Disable halt on reset
            if (!swd_write_word(DBG_EMCR, 0)) {
                return 0;
            }

            break;

        case NO_DEBUG:
            if (!swd_write_word(DBG_HCSR, DBGKEY)) {
                return 0;
            }

            break;

        case DEBUG:
            if (!JTAG2SWD()) {
                return 0;
            }

            if (!swd_write_dp(DP_ABORT, STKCMPCLR | STKERRCLR | WDERRCLR | ORUNERRCLR)) {
                return 0;
            }

            // Ensure CTRL/STAT register selected in DPBANKSEL
            if (!swd_write_dp(DP_SELECT, 0)) {
                return 0;
            }

            // Power up
            if (!swd_write_dp(DP_CTRL_STAT, CSYSPWRUPREQ | CDBGPWRUPREQ)) {
                return 0;
            }

            // Enable debug
            if (!swd_write_word(DBG_HCSR, DBGKEY | C_DEBUGEN)) {
                return 0;
            }

            break;

        case HALT:
            if (!swd_init_debug()) {
                return 0;
            }

            // Enable debug and halt the core (DHCSR <- 0xA05F0003)
            if (!swd_write_word(DBG_HCSR, DBGKEY | C_DEBUGEN | C_HALT)) {
                return 0;
            }

            // Wait until core is halted
            do {
                if (!swd_read_word(DBG_HCSR, &val)) {
                    return 0;
                }
            } while ((val & S_HALT) == 0);
            break;

        case RUN:
            if (!swd_write_word(DBG_HCSR, DBGKEY)) {
                return 0;
            }
            swd_off();

        default:
            return 0;
    }

    return 1;
}

uint8_t swd_set_target_state_sw(TARGET_RESET_STATE state)
{
    uint32_t val;

    /* Calling swd_init prior to enterring RUN state causes operations to fail. */
    if (state != RUN) {
        swd_init();
    }

    switch (state) {
        case RESET_HOLD:
            swd_set_target_reset(1);
            break;

        case RESET_RUN:
            swd_set_target_reset(1);
            delaymS(20);
            swd_set_target_reset(0);
            delaymS(20);
            swd_off();
            break;

        case RESET_PROGRAM:
            if (!swd_init_debug()) {
                return 0;
            }

            // Enable debug and halt the core (DHCSR <- 0xA05F0003)
            if (!swd_write_word(DBG_HCSR, DBGKEY | C_DEBUGEN | C_HALT)) {
                return 0;
            }

            // Wait until core is halted
            do {
                if (!swd_read_word(DBG_HCSR, &val)) {
                    return 0;
                }
            } while ((val & S_HALT) == 0);

            // Enable halt on reset
            if (!swd_write_word(DBG_EMCR, VC_CORERESET)) {
                return 0;
            }

            // Perform a soft reset
            if (!swd_read_word(NVIC_AIRCR, &val)) {
                return 0;
            }

            if (!swd_write_word(NVIC_AIRCR, VECTKEY | (val & SCB_AIRCR_PRIGROUP_Msk) | SYSRESETREQ)) {
                return 0;
            }

            delaymS(20);

            do {
                if (!swd_read_word(DBG_HCSR, &val)) {
                    return 0;
                }
            } while ((val & S_HALT) == 0);

            // Disable halt on reset
            if (!swd_write_word(DBG_EMCR, 0)) {
                return 0;
            }

            break;

        case NO_DEBUG:
            if (!swd_write_word(DBG_HCSR, DBGKEY)) {
                return 0;
            }

            break;

        case DEBUG:
            if (!JTAG2SWD()) {
                return 0;
            }

            if (!swd_write_dp(DP_ABORT, STKCMPCLR | STKERRCLR | WDERRCLR | ORUNERRCLR)) {
                return 0;
            }

            // Ensure CTRL/STAT register selected in DPBANKSEL
            if (!swd_write_dp(DP_SELECT, 0)) {
                return 0;
            }

            // Power up
            if (!swd_write_dp(DP_CTRL_STAT, CSYSPWRUPREQ | CDBGPWRUPREQ)) {
                return 0;
            }

            // Enable debug
            if (!swd_write_word(DBG_HCSR, DBGKEY | C_DEBUGEN)) {
                return 0;
            }

            break;

        case HALT:
            if (!swd_init_debug()) {
                return 0;
            }

            // Enable debug and halt the core (DHCSR <- 0xA05F0003)
            if (!swd_write_word(DBG_HCSR, DBGKEY | C_DEBUGEN | C_HALT)) {
                return 0;
            }

            // Wait until core is halted
            do {
                if (!swd_read_word(DBG_HCSR, &val)) {
                    return 0;
                }
            } while ((val & S_HALT) == 0);
            break;

        case RUN:
            if (!swd_write_word(DBG_HCSR, DBGKEY)) {
                return 0;
            }
            swd_off();

        default:
            return 0;
    }

    return 1;
}