How to use sigprocmask to synchronize processes ?

Why is the necessity for watchdog timers in so many embedded systems?

LAB4 – Using the 8051 Timers in polling mode   Overview   The purpose of this lab is to control and program the MC8051 Timers of the micro-controller in a given sequence. The program reads port 0 (P0) and outputs its value on port 1 (P1). P0 input is incremented at a controlled rate and displayed on P2. Display update takes place once at the end of a sequence including Timer0 overflow followed by Timer1 overflow. Timer0 and Timer1 are programmed using the polling mode, no interrupts. The status of TF0 and TF1 are displayed on Port 3 bit 0 (P3.0) and bit 1 (P3.1) respectively.   Steps   First, configure and initialize the required parallel ports; Timer 0 to mode 1, and Timer1 to mode 1. The Main program starts at code memory address 40H, the main program only function is reading P0, updating P1 and P2, and displaying the two overflow flags on port 3 two bits. Second, in the main program configure the two timers, Timer0 and Timer1, for Mode 1 with maximum delay time. Start Timer0, read…

What does it mean to refer to a PLD process technology as being "volatile," and which PLDs fall within this category of volatile PLDs?