Electronic – Dump Flash Memory through a single GPIO pin

I'm working with Infineon's XMC4500 Relax Kit and I'm trying to extract the firmware through a single GPIO pin.

My very naive idea is to dump one bit at a time through the GPIO pin and somehow "sniff" the data with a logic analyzer.

Pseudocode:

while(word by word memory copy hasn't finished)
  ...
  register = value;
  temp_value = value AND 0x1;
  pin = temp_value;
  value = value >> 1;
  ...

Am I on the right track? Does anybody have a better/nicer idea how to archive this?

### EDIT ###

Actually a requirement of my (shell)code would be that it needs to be really tiny. I found this nifty trick on how to
dump firmware by blinking the LEDs.

However I'm struggling to receive correct values with Saleae Logic Analyzer.

Basically what I'm doing is:

1. Setup the GPIO pin directions to output
2. Blink LED1 (pin 1.1) with a clock (SPI serial clock)
3. Blink LED2 (pin 1.0) with data bits (SPI MOSI)
4. Sniff pins with a logic analyzer

Here's my C code:

#include "XMC4500.h"

#define DEL 1260

void init() 
{
  // P1.0 output, push pull
  PORT1->IOCR0 = 0x80UL << 0;
  // P1.1 output, push pull
  PORT1->IOCR0 |= 0x80UL << 8;
}

void delay(int i) { 
  while(--i) { 
    asm("nop\n"); 
    asm("nop\n"); 
  } 
}

// Sets a pin to high
// P1.0 = SPI MOSI
// P1.1 = SPI CLOCK
void output_high(int i) {
  // P1.0 high
  if(i == 0) {
    PORT1->OUT |= 0x1UL;  
  }

  // P1.1 high
  if(i == 1) {
    PORT1->OUT |= 0x2UL;
  } 
}

// Sets a pin to low
// P1.0 = SPI MOSI
// P1.1 = SPI CLOCK
void output_low(int i) {
  // P1.0 low
  if(i == 0) {
    PORT1->OUT &= (~0x1UL);
  }

  // P1.1 low
  if(i == 1) {
    PORT1->OUT &= (~0x2UL);
  }
}

// SPI bit banging
void spi_send_byte(unsigned char data)
{
  int i;

  // Send bits 7..0
  for (i = 0; i < 8; i++)
  {
    // Sets P1.1 to low (serial clock)
    output_low(1);

    // Consider leftmost bit
    // Set line high if bit is 1, low if bit is 0
    if (data & 0x80)
      // Sets P1.0 to high (MOSI)
      output_high(0);
    else
      // Sets P1.0 to low (MOSI)
      output_low(0);

    delay(DEL);

    // Sets P1.1 to high (Serial Clock)
    output_high(1);

    // Shift byte left so next bit will be leftmost
    data <<= 1;
  }
}

int main() {
  init();

  while(1) {
    spi_send_byte('t');
    spi_send_byte('e');
    spi_send_byte('s');
    spi_send_byte('t');
  }

  return 0;
}

### 2nd EDIT ###

Finally sorted it out. Dumping flash memory is working fine with the following code:

#include "XMC4500.h"

// SPI bit banging
void spi_send_word(uint32_t data)
{
  int i;

  // LSB first, 32 bits per transfer
  for (i = 0; i < 32; i++)
  {
    // set pin 1.1 to low (SPI clock)
    PORT1->OUT &= (~0x2UL);

    // set line high if bit is 1, low if bit is 0
    if (data & 0x1) {
      // set pin 1.0 to high (SPI MOSI)
      PORT1->OUT |= 0x1UL;
    }
    else {
      // set pin 1.0 to low (SPI MOSI)
      PORT1->OUT &= (~0x1UL);   
    }

    // set pin 1.1 to high (SPI clock)
    PORT1->OUT |= 0x2UL;

    data >>= 1;
  }
}

int main() {
  // start dumping at memory address 0x08000000
  unsigned int *p;
  p = (uint32_t *)(0x08000000u);

  // configure pin 1.0 and pin 1.1 as output (push-pull)
  PORT1->IOCR0 = 0x8080UL;

  while(1) {
    spi_send_word(*p);
    p++;
  }
}