1. Are all pins set to Alternate Function Mode 0 when the board powers-up?
2. If question 1 is true, then what function is set on header P1, pin 12? BCM2835 ARM Peripherals.pdf Table 6-31 indicates pin 12 in alt-0 mode would have a PW-M0 function assignment. While, the Raspberry Pi Revision 2 Schematics show GPIO18 coming out of chip IO1 is labeled GPIO_GEN1 (sheet 2 of 5) and it is wired directly to header P1 Pin 12 and that pad is also labeled GPIO_GEN1 (also sheet 2 of 5). So I am confused as to which is correct.
3. The other possibility is that all pins default to GPIO mode when the board powers-up and to attain the special functions like, UART, I2C and SPI then each respective pin must be set to its respective alternate function mode.