replace msleep() by thread signalling in comms.c

[proxmark3-svn] / armsrc / util.c

//-----------------------------------------------------------------------------
// Jonathan Westhues, Sept 2005
//
// This code is licensed to you under the terms of the GNU GPL, version 2 or,
// at your option, any later version. See the LICENSE.txt file for the text of
// the license.
//-----------------------------------------------------------------------------
// Utility functions used in many places, not specific to any piece of code.
//-----------------------------------------------------------------------------

#include "proxmark3.h"
#include "util.h"
#include "string.h"
#include "apps.h"
#include "BigBuf.h"



void print_result(char *name, uint8_t *buf, size_t len) {
   uint8_t *p = buf;

   if ( len % 16 == 0 ) {
           for(; p-buf < len; p += 16)
           Dbprintf("[%s:%d/%d] %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x %02x",
                                name,
                                p-buf,
                                len,
                                p[0], p[1], p[2], p[3], p[4], p[5], p[6], p[7],p[8], p[9], p[10], p[11], p[12], p[13], p[14], p[15]
           );
   }
   else {
   for(; p-buf < len; p += 8)
           Dbprintf("[%s:%d/%d] %02x %02x %02x %02x %02x %02x %02x %02x", name, p-buf, len, p[0], p[1], p[2], p[3], p[4], p[5], p[6], p[7]);
   }
}

size_t nbytes(size_t nbits) {
        return (nbits >> 3)+((nbits % 8) > 0);
}

uint32_t SwapBits(uint32_t value, int nrbits) {
        int i;
        uint32_t newvalue = 0;
        for(i = 0; i < nrbits; i++) {
                newvalue ^= ((value >> i) & 1) << (nrbits - 1 - i);
        }
        return newvalue;
}

void num_to_bytes(uint64_t n, size_t len, uint8_t* dest)
{
        while (len--) {
                dest[len] = (uint8_t) n;
                n >>= 8;
        }
}

uint64_t bytes_to_num(uint8_t* src, size_t len)
{
        uint64_t num = 0;
        while (len--)
        {
                num = (num << 8) | (*src);
                src++;
        }
        return num;
}

// RotateLeft - Ultralight, Desfire
void rol(uint8_t *data, const size_t len){
        uint8_t first = data[0];
        for (size_t i = 0; i < len-1; i++) {
                data[i] = data[i+1];
        }
        data[len-1] = first;
}
void lsl (uint8_t *data, size_t len) {
        for (size_t n = 0; n < len - 1; n++) {
                data[n] = (data[n] << 1) | (data[n+1] >> 7);
        }
        data[len - 1] <<= 1;
}

void LEDsoff()
{
        LED_A_OFF();
        LED_B_OFF();
        LED_C_OFF();
        LED_D_OFF();
}

void LEDson()
{
        LED_A_ON();
        LED_B_ON();
        LED_C_ON();
        LED_D_ON();
}

void LEDsinvert()
{
        LED_A_INV();
        LED_B_INV();
        LED_C_INV();
        LED_D_INV();
}

// LEDs: R(C) O(A) G(B) -- R(D) [1, 2, 4 and 8]
void LED(int led, int ms)
{
        if (led & LED_RED)
                LED_C_ON();
        if (led & LED_ORANGE)
                LED_A_ON();
        if (led & LED_GREEN)
                LED_B_ON();
        if (led & LED_RED2)
                LED_D_ON();

        if (!ms)
                return;

        SpinDelay(ms);

        if (led & LED_RED)
                LED_C_OFF();
        if (led & LED_ORANGE)
                LED_A_OFF();
        if (led & LED_GREEN)
                LED_B_OFF();
        if (led & LED_RED2)
                LED_D_OFF();
}


// Determine if a button is double clicked, single clicked,
// not clicked, or held down (for ms || 1sec)
// In general, don't use this function unless you expect a
// double click, otherwise it will waste 500ms -- use BUTTON_HELD instead
int BUTTON_CLICKED(int ms)
{
        // Up to 500ms in between clicks to mean a double click
        int ticks = (48000 * (ms ? ms : 1000)) >> 10;

        // If we're not even pressed, forget about it!
        if (!BUTTON_PRESS())
                return BUTTON_NO_CLICK;

        // Borrow a PWM unit for my real-time clock
        AT91C_BASE_PWMC->PWMC_ENA = PWM_CHANNEL(0);
        // 48 MHz / 1024 gives 46.875 kHz
        AT91C_BASE_PWMC_CH0->PWMC_CMR = PWM_CH_MODE_PRESCALER(10);
        AT91C_BASE_PWMC_CH0->PWMC_CDTYR = 0;
        AT91C_BASE_PWMC_CH0->PWMC_CPRDR = 0xffff;

        uint16_t start = AT91C_BASE_PWMC_CH0->PWMC_CCNTR;

        int letoff = 0;
        for(;;)
        {
                uint16_t now = AT91C_BASE_PWMC_CH0->PWMC_CCNTR;

                // We haven't let off the button yet
                if (!letoff)
                {
                        // We just let it off!
                        if (!BUTTON_PRESS())
                        {
                                letoff = 1;

                                // reset our timer for 500ms
                                start = AT91C_BASE_PWMC_CH0->PWMC_CCNTR;
                                ticks = (48000 * (500)) >> 10;
                        }

                        // Still haven't let it off
                        else
                                // Have we held down a full second?
                                if (now == (uint16_t)(start + ticks))
                                        return BUTTON_HOLD;
                }

                // We already let off, did we click again?
                else
                        // Sweet, double click!
                        if (BUTTON_PRESS())
                                return BUTTON_DOUBLE_CLICK;

                        // Have we ran out of time to double click?
                        else
                                if (now == (uint16_t)(start + ticks))
                                        // At least we did a single click
                                        return BUTTON_SINGLE_CLICK;

                WDT_HIT();
        }

        // We should never get here
        return BUTTON_ERROR;
}

// Determine if a button is held down
int BUTTON_HELD(int ms)
{
        // If button is held for one second
        int ticks = (48000 * (ms ? ms : 1000)) >> 10;

        // If we're not even pressed, forget about it!
        if (!BUTTON_PRESS())
                return BUTTON_NO_CLICK;

        // Borrow a PWM unit for my real-time clock
        AT91C_BASE_PWMC->PWMC_ENA = PWM_CHANNEL(0);
        // 48 MHz / 1024 gives 46.875 kHz
        AT91C_BASE_PWMC_CH0->PWMC_CMR = PWM_CH_MODE_PRESCALER(10);
        AT91C_BASE_PWMC_CH0->PWMC_CDTYR = 0;
        AT91C_BASE_PWMC_CH0->PWMC_CPRDR = 0xffff;

        uint16_t start = AT91C_BASE_PWMC_CH0->PWMC_CCNTR;

        for(;;)
        {
                uint16_t now = AT91C_BASE_PWMC_CH0->PWMC_CCNTR;

                // As soon as our button let go, we didn't hold long enough
                if (!BUTTON_PRESS())
                        return BUTTON_SINGLE_CLICK;

                // Have we waited the full second?
                else
                        if (now == (uint16_t)(start + ticks))
                                return BUTTON_HOLD;

                WDT_HIT();
        }

        // We should never get here
        return BUTTON_ERROR;
}

// attempt at high resolution microsecond timer
// beware: timer counts in 21.3uS increments (1024/48Mhz)
void SpinDelayUs(int us)
{
        int ticks = (48*us) >> 10;

        // Borrow a PWM unit for my real-time clock
        AT91C_BASE_PWMC->PWMC_ENA = PWM_CHANNEL(0);
        // 48 MHz / 1024 gives 46.875 kHz
        AT91C_BASE_PWMC_CH0->PWMC_CMR = PWM_CH_MODE_PRESCALER(10);
        AT91C_BASE_PWMC_CH0->PWMC_CDTYR = 0;
        AT91C_BASE_PWMC_CH0->PWMC_CPRDR = 0xffff;

        uint16_t start = AT91C_BASE_PWMC_CH0->PWMC_CCNTR;

        for(;;) {
                uint16_t now = AT91C_BASE_PWMC_CH0->PWMC_CCNTR;
                if (now == (uint16_t)(start + ticks))
                        return;

                WDT_HIT();
        }
}

void SpinDelay(int ms)
{
  // convert to uS and call microsecond delay function
        SpinDelayUs(ms*1000);
}

/* Similar to FpgaGatherVersion this formats stored version information
 * into a string representation. It takes a pointer to the struct version_information,
 * verifies the magic properties, then stores a formatted string, prefixed by
 * prefix in dst.
 */
void FormatVersionInformation(char *dst, int len, const char *prefix, void *version_information)
{
        struct version_information *v = (struct version_information*)version_information;
        dst[0] = 0;
        strncat(dst, prefix, len-1);
        if(v->magic != VERSION_INFORMATION_MAGIC) {
                strncat(dst, "Missing/Invalid version information\n", len - strlen(dst) - 1);
                return;
        }
        if(v->versionversion != 1) {
                strncat(dst, "Version information not understood\n", len - strlen(dst) - 1);
                return;
        }
        if(!v->present) {
                strncat(dst, "Version information not available\n", len - strlen(dst) - 1);
                return;
        }

        strncat(dst, v->gitversion, len - strlen(dst) - 1);
        if(v->clean == 0) {
                strncat(dst, "-unclean", len - strlen(dst) - 1);
        } else if(v->clean == 2) {
                strncat(dst, "-suspect", len - strlen(dst) - 1);
        }

        strncat(dst, " ", len - strlen(dst) - 1);
        strncat(dst, v->buildtime, len - strlen(dst) - 1);
        strncat(dst, "\n", len - strlen(dst) - 1);
}


//  -------------------------------------------------------------------------
//  timer lib
//  -------------------------------------------------------------------------
//  test procedure:
//
//  ti = GetTickCount();
//  SpinDelay(1000);
//  ti = GetTickCount() - ti;
//  Dbprintf("timer(1s): %d t=%d", ti, GetTickCount());

void StartTickCount()
{
        // This timer is based on the slow clock. The slow clock frequency is between 22kHz and 40kHz.
        // We can determine the actual slow clock frequency by looking at the Main Clock Frequency Register.
        uint16_t mainf = AT91C_BASE_PMC->PMC_MCFR & 0xffff;     // = 16 * main clock frequency (16MHz) / slow clock frequency
        // set RealTimeCounter divider to count at 1kHz:
        AT91C_BASE_RTTC->RTTC_RTMR = AT91C_RTTC_RTTRST | ((256000 + (mainf/2)) / mainf);
        // note: worst case precision is approx 2.5%
}


/*
* Get the current count.
*/
uint32_t RAMFUNC GetTickCount(){
        return AT91C_BASE_RTTC->RTTC_RTVR;// was * 2;
}


//  -------------------------------------------------------------------------
//  microseconds timer
//  -------------------------------------------------------------------------
void StartCountUS()
{
        AT91C_BASE_PMC->PMC_PCER |= (0x1 << 12) | (0x1 << 13) | (0x1 << 14);
//  AT91C_BASE_TCB->TCB_BMR = AT91C_TCB_TC1XC1S_TIOA0;
        AT91C_BASE_TCB->TCB_BMR = AT91C_TCB_TC0XC0S_NONE | AT91C_TCB_TC1XC1S_TIOA0 | AT91C_TCB_TC2XC2S_NONE;

        // fast clock
        AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKDIS; // timer disable
        AT91C_BASE_TC0->TC_CMR = AT91C_TC_CLKS_TIMER_DIV3_CLOCK | // MCK(48MHz)/32 -- tick=1.5mks
                                                                                                                AT91C_TC_WAVE | AT91C_TC_WAVESEL_UP_AUTO | AT91C_TC_ACPA_CLEAR |
                                                                                                                AT91C_TC_ACPC_SET | AT91C_TC_ASWTRG_SET;
        AT91C_BASE_TC0->TC_RA = 1;
        AT91C_BASE_TC0->TC_RC = 0xBFFF + 1; // 0xC000

        AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS; // timer disable
        AT91C_BASE_TC1->TC_CMR = AT91C_TC_CLKS_XC1; // from timer 0

        AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKEN;
        AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKEN;
        AT91C_BASE_TCB->TCB_BCR = 1;
        }


uint32_t RAMFUNC GetCountUS(){
        return (AT91C_BASE_TC1->TC_CV * 0x8000) + ((AT91C_BASE_TC0->TC_CV * 2) / 3); //was  /15) * 10);
}


static uint32_t GlobalUsCounter = 0;

uint32_t RAMFUNC GetDeltaCountUS(){
        uint32_t g_cnt = GetCountUS();
        uint32_t g_res = g_cnt - GlobalUsCounter;
        GlobalUsCounter = g_cnt;
        return g_res;
}


//  -------------------------------------------------------------------------
//  Timer for iso14443 commands. Uses ssp_clk from FPGA
//  -------------------------------------------------------------------------
void StartCountSspClk()
{
        AT91C_BASE_PMC->PMC_PCER = (1 << AT91C_ID_TC0) | (1 << AT91C_ID_TC1) | (1 << AT91C_ID_TC2);  // Enable Clock to all timers
        AT91C_BASE_TCB->TCB_BMR = AT91C_TCB_TC0XC0S_TIOA1       // XC0 Clock = TIOA1
                                                        | AT91C_TCB_TC1XC1S_NONE        // XC1 Clock = none
                                                        | AT91C_TCB_TC2XC2S_TIOA0;      // XC2 Clock = TIOA0

        // configure TC1 to create a short pulse on TIOA1 when a rising edge on TIOB1 (= ssp_clk from FPGA) occurs:
        AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS;               // disable TC1
        AT91C_BASE_TC1->TC_CMR = AT91C_TC_CLKS_TIMER_DIV1_CLOCK // TC1 Clock = MCK(48MHz)/2 = 24MHz
                                                        | AT91C_TC_CPCSTOP              // Stop clock on RC compare
                                                        | AT91C_TC_EEVTEDG_RISING       // Trigger on rising edge of Event
                                                        | AT91C_TC_EEVT_TIOB            // Event-Source: TIOB1 (= ssp_clk from FPGA = 13,56MHz/16 ... 13,56MHz/4)
                                                        | AT91C_TC_ENETRG               // Enable external trigger event
                                                        | AT91C_TC_WAVESEL_UP           // Upmode without automatic trigger on RC compare
                                                        | AT91C_TC_WAVE                 // Waveform Mode
                                                        | AT91C_TC_AEEVT_SET            // Set TIOA1 on external event
                                                        | AT91C_TC_ACPC_CLEAR;          // Clear TIOA1 on RC Compare
        AT91C_BASE_TC1->TC_RC = 0x02;                           // RC Compare value = 0x02

        // use TC0 to count TIOA1 pulses
        AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKDIS;               // disable TC0
        AT91C_BASE_TC0->TC_CMR = AT91C_TC_CLKS_XC0              // TC0 clock = XC0 clock = TIOA1
                                                        | AT91C_TC_WAVE                 // Waveform Mode
                                                        | AT91C_TC_WAVESEL_UP           // just count
                                                        | AT91C_TC_ACPA_CLEAR           // Clear TIOA0 on RA Compare
                                                        | AT91C_TC_ACPC_SET;            // Set TIOA0 on RC Compare
        AT91C_BASE_TC0->TC_RA = 1;                              // RA Compare value = 1; pulse width to TC2
        AT91C_BASE_TC0->TC_RC = 0;                              // RC Compare value = 0; increment TC2 on overflow

        // use TC2 to count TIOA0 pulses (giving us a 32bit counter (TC0/TC2) clocked by ssp_clk)
        AT91C_BASE_TC2->TC_CCR = AT91C_TC_CLKDIS;               // disable TC2
        AT91C_BASE_TC2->TC_CMR = AT91C_TC_CLKS_XC2              // TC2 clock = XC2 clock = TIOA0
                                                        | AT91C_TC_WAVE                 // Waveform Mode
                                                        | AT91C_TC_WAVESEL_UP;          // just count

        AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKEN;                // enable TC0
        AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKEN;                // enable TC1
        AT91C_BASE_TC2->TC_CCR = AT91C_TC_CLKEN;                // enable TC2

        //
        // synchronize the counter with the ssp_frame signal. Note: FPGA must be in a FPGA mode with SSC transfer, otherwise SSC_FRAME and SSC_CLK signals would not be present
        //
        while(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_FRAME);      // wait for ssp_frame to be low
        while(!(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_FRAME));   // wait for ssp_frame to go high (start of frame)
        while(!(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK));     // wait for ssp_clk to go high; 1st ssp_clk after start of frame
        while(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK);        // wait for ssp_clk to go low;
        while(!(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK));     // wait for ssp_clk to go high; 2nd ssp_clk after start of frame
        if ((AT91C_BASE_SSC->SSC_RFMR & SSC_FRAME_MODE_BITS_IN_WORD(32)) == SSC_FRAME_MODE_BITS_IN_WORD(16)) {
                while(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK);    // wait for ssp_clk to go low;
                while(!(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK)); // wait for ssp_clk to go high; 3rd ssp_clk after start of frame
                while(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK);    // wait for ssp_clk to go low;
                while(!(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK)); // wait for ssp_clk to go high; 4th ssp_clk after start of frame
                while(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK);    // wait for ssp_clk to go low;
                while(!(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK)); // wait for ssp_clk to go high; 5th ssp_clk after start of frame
                while(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK);    // wait for ssp_clk to go low;
                while(!(AT91C_BASE_PIOA->PIO_PDSR & GPIO_SSC_CLK)); // wait for ssp_clk to go high; 6th ssp_clk after start of frame
        }
        // it is now safe to assert a sync signal. This sets all timers to 0 on next active clock edge
        AT91C_BASE_TCB->TCB_BCR = 1;                            // assert Sync (set all timers to 0 on next active clock edge)
        // at the next (3rd/7th) ssp_clk rising edge, TC1 will be reset (and not generate a clock signal to TC0)
        // at the next (4th/8th) ssp_clk rising edge, TC0 (the low word of our counter) will be reset. From now on,
        // whenever the last three bits of our counter go 0, we can be sure to be in the middle of a frame transfer.
        // (just started with the transfer of the 3rd Bit).
        // The high word of the counter (TC2) will not reset until the low word (TC0) overflows. Therefore need to wait quite some time before
        // we can use the counter.
        while (AT91C_BASE_TC0->TC_CV < 0xFFFF);
        // Note: needs one more SSP_CLK cycle (1.18 us) until TC2 resets. Don't call GetCountSspClk() that soon.
}


void ResetSspClk(void) {
        //enable clock of timer and software trigger
        AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
        AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
        AT91C_BASE_TC2->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
        while (AT91C_BASE_TC2->TC_CV > 0);
}

uint32_t GetCountSspClk(){
        uint32_t hi, lo;

        do { 
                hi = AT91C_BASE_TC2->TC_CV;
                lo = AT91C_BASE_TC0->TC_CV;
        } while (hi != AT91C_BASE_TC2->TC_CV);
        
        return (hi << 16) | lo;
}

//  -------------------------------------------------------------------------
//  Timer for bitbanging, or LF stuff when you need a very precis timer
//  1us = 1.5ticks
//  -------------------------------------------------------------------------
void StartTicks(void){
        // initialization of the timer
        AT91C_BASE_PMC->PMC_PCER |= (1 << AT91C_ID_TC0) | (1 << AT91C_ID_TC1);
        AT91C_BASE_TCB->TCB_BMR = AT91C_TCB_TC0XC0S_NONE | AT91C_TCB_TC1XC1S_TIOA0 | AT91C_TCB_TC2XC2S_NONE;

        // disable TC0 and TC1 for re-configuration
        AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKDIS;
        AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS;

        // first configure TC1 (higher, 0xFFFF0000) 16 bit counter
        AT91C_BASE_TC1->TC_CMR = AT91C_TC_CLKS_XC1; // just connect to TIOA0 from TC0
        AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG; // re-enable timer and wait for TC0

        // second configure TC0 (lower, 0x0000FFFF) 16 bit counter
        AT91C_BASE_TC0->TC_CMR = AT91C_TC_CLKS_TIMER_DIV3_CLOCK | // MCK(48MHz) / 32
                                                         AT91C_TC_WAVE | AT91C_TC_WAVESEL_UP_AUTO |
                                                         AT91C_TC_ACPA_CLEAR | // RA comperator clears TIOA (carry bit)
                                                         AT91C_TC_ACPC_SET |   // RC comperator sets TIOA (carry bit)
                                                         AT91C_TC_ASWTRG_SET;  // SWTriger sets TIOA (carry bit)
        AT91C_BASE_TC0->TC_RC  = 0; // set TIOA (carry bit) on overflow, return to zero
        AT91C_BASE_TC0->TC_RA  = 1; // clear carry bit on next clock cycle
        AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG; // reset and re-enable timer

        // synchronized startup procedure
        while (AT91C_BASE_TC0->TC_CV > 0); // wait until TC0 returned to zero
        while (AT91C_BASE_TC0->TC_CV < 2); // and has started (TC_CV > TC_RA, now TC1 is cleared)

        // return to zero
        AT91C_BASE_TC1->TC_CCR = AT91C_TC_SWTRG;
        AT91C_BASE_TC0->TC_CCR = AT91C_TC_SWTRG;
        while (AT91C_BASE_TC0->TC_CV > 0);
}


uint32_t GetTicks(void) {
        uint32_t hi, lo;

        do {
                hi = AT91C_BASE_TC1->TC_CV;
                lo = AT91C_BASE_TC0->TC_CV;
        } while(hi != AT91C_BASE_TC1->TC_CV);

        return (hi << 16) | lo;
}


// Wait - Spindelay in ticks.
// if called with a high number, this will trigger the WDT...
void WaitTicks(uint32_t ticks){
        if ( ticks == 0 ) return;
        ticks += GetTicks();
        while (GetTicks() < ticks);
}


// Wait / Spindelay in us (microseconds)
// 1us = 1.5ticks.
void WaitUS(uint16_t us){
        WaitTicks( (uint32_t)us * 3 / 2 ) ;
}


void WaitMS(uint16_t ms){
        WaitTicks( (uint32_t)ms * 1500 );
}


// Starts Clock and waits until its reset
void ResetTicks(void){
        AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
        AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
        while (AT91C_BASE_TC0->TC_CV > 0);
}


void ResetTimer(AT91PS_TC timer){
        timer->TC_CCR = AT91C_TC_CLKEN | AT91C_TC_SWTRG;
        while(timer->TC_CV > 0) ;
}


// stop clock
void StopTicks(void){
        AT91C_BASE_TC0->TC_CCR = AT91C_TC_CLKDIS;
        AT91C_BASE_TC1->TC_CCR = AT91C_TC_CLKDIS;
}


static uint64_t next_random = 1;

/* Generates a (non-cryptographically secure) 32-bit random number.
 *
 * We don't have an implementation of the "rand" function or a clock to seed it
 * with, so we just call GetTickCount the first time to seed ourselves.
 */
uint32_t prand() {
        if (next_random == 1) {
                next_random = GetTickCount();
        }

        next_random = next_random * 6364136223846793005 + 1;
        return (uint32_t)(next_random >> 32) % 0xffffffff;
}