So I'm trying to read a bit of data via SWD. I've tried two chips as target - LPC1110 and STM32F030F4 (the first of them I used for other schematic, but I've reset the flash to make sure the pins are not configured improperly).

I use Arduino as a host. I wire D3 to SWCLK and D4 to SWDIO (with pull-up to 3.3V line). I fail miserably with both chips - i.e. when I expect some ACK be read - it only shows HIGH state on the line all the time.

Here is my code. Could anyone have a look and tell where I went wrong:

int swdck = 3;
int swdio = 4;

void setup() {                
  pinMode(swdck, OUTPUT);
  digitalWrite(swdck, HIGH);
  pinMode(swdio, INPUT);
  digitalWrite(swdio, HIGH);
  Serial.begin(9600);
}

// write some bits from X (least significant first) to SWD
void clockOut(int x, int bits) {
  pinMode(swdio, OUTPUT);
  while (bits > 0) {
    digitalWrite(swdck, LOW);
    digitalWrite(swdio, (x & 1) ? HIGH : LOW);
    delay(1);
    digitalWrite(swdck, HIGH);
    delay(1);
    bits--;
    x >>= 1;
  }
  pinMode(swdio, INPUT);
  digitalWrite(swdio, HIGH);
}

// read some bits from SWD, least significant first
int clockIn(int bits) {
  pinMode(swdio, INPUT);
  digitalWrite(swdio, HIGH);
  int i, res;
  res = 0;
  for (i = 0; i < bits; i++) {
    digitalWrite(swdck, LOW);
    delay(1);
    if (digitalRead(swdio) == HIGH) {
      res += (1 << i);
    }
    digitalWrite(swdck, HIGH);
    delay(1);
  }
  return res;
}

void loop() {
  int x;
  // unlock sequence though it probably is not needed
  clockIn(26); clockIn(26); // more than 50 clocks
  clockOut(0xE79E, 16); // command to switch to SWD
  clockIn(26); clockIn(26);

  clockOut(0x25, 7); // 0b0100101 - request to read Debug-port-0, i.e. ID
  x = clockIn(5); // there should be ACK bits somewhere... but I get 0x1111
  clockIn(26); clockIn(26); // perform more readings for case anything is returned
  Serial.println(x);
  delay(1000);
}