It's a TI TSC2046 controller, hooked up to the ARM7 SPI port. News at 9.

Command Format:

Power down mode:

/PENIRQ is wired to bit 6 of R2_CR

The DS has wired an external VREF of 3.3 V to the TSC, instead of using the internal 2.5 VREF. This impacts the temperature calculations below, and converting any reading into an actual voltage.

Useful commands:

A 12-bit measurment cycle consists of 3 SPI byte transfers:

• The first transfer sends the command and returns no meaningful data.
• The second transfer returns 0 measurement(11)..measurment(5)
• The third transfer returns measurment(4..0) 000

Thus, pseudocode for measuring a TSC input is:

 
BlockingWriteSPI(command);
data = BlockingWriteSPI(0);
data = (data << 5) | (BlockingWriteSPI(0) >> 3);

Temperature calculation:

Temperature diode two has a 91 times larger current, and the absolute temperature can be calculated based on the measurements of the two sensors. I'll present a fixed point algorithm for computing the temperature in degrees C (see the TSC 2046 datasheet for the original equation).

Reading from the touchscreen controller (SPI)

 
uint16 touchRead(uint32 command) {
  uint16 result;
  while (SERIAL_CR & SERIAL_BUSY) swiDelay(1);

  // Write the command and wait for it to complete
  SERIAL_CR = SERIAL_ENABLE | 0x800 | 0x201;
  SERIAL_DATA = command;
  while (SERIAL_CR & SERIAL_BUSY) swiDelay(1);

  // Write the second command and clock in part of the data
  SERIAL_DATA = 0;
  while (SERIAL_CR & SERIAL_BUSY) swiDelay(1);
  result = SERIAL_DATA;

  // Clock in the rest of the data (last transfer)
  SERIAL_CR = SERIAL_ENABLE | 0x201;
  SERIAL_DATA = 0;
  while (SERIAL_CR & SERIAL_BUSY) swiDelay(1);

  // Return the result
  return ((result & 0x7F) << 5) | (SERIAL_DATA >> 3);
}

Todo: figure out what bit 11, bit 9, and bit 0 are doing (bit 0 is probably the CR select, since the firmware reads have this bit cleared)

Position calculation

 
#define SCREEN_WIDTH   256
#define SCREEN_HEIGHT   192

// those are pixel positions of the two points you click when calibrating
#define TOUCH_CNTRL_X1   (*(vu8*)0x027FFCDC)
#define TOUCH_CNTRL_Y1   (*(vu8*)0x027FFCDD)
#define TOUCH_CNTRL_X2   (*(vu8*)0x027FFCE2)
#define TOUCH_CNTRL_Y2   (*(vu8*)0x027FFCE3)

// those are the corresponding touchscreen values:
#define TOUCH_CAL_X1   (*(vu16*)0x027FFCD8)
#define TOUCH_CAL_Y1   (*(vu16*)0x027FFCDA)
#define TOUCH_CAL_X2   (*(vu16*)0x027FFCDE)
#define TOUCH_CAL_Y2   (*(vu16*)0x027FFCE0)

// linear mapping can be used to go from touchscreen position to pixel position

// precalculate some values
static int16 TOUCH_WIDTH  = TOUCH_CAL_X2 - TOUCH_CAL_X1;
static int16 TOUCH_HEIGHT = TOUCH_CAL_Y2 - TOUCH_CAL_Y1;
static int16 CNTRL_WIDTH  = TOUCH_CNTRL_X2 - TOUCH_CNTRL_X1;
static int16 CNTRL_HEIGHT = TOUCH_CNTRL_Y2 - TOUCH_CNTRL_Y1;


// reading pixel position:
int16 x = (IPC->touchX - (int16) TOUCH_CAL_X1) * CNTRL_WIDTH  / TOUCH_WIDTH  + (int16) TOUCH_CNTRL_X1;
int16 y = (IPC->touchY - (int16) TOUCH_CAL_Y1) * CNTRL_HEIGHT / TOUCH_HEIGHT + (int16) TOUCH_CNTRL_Y1;