CS 452/652 Spring 2022 - Lecture 2

May 5, 2022 prev next

Chapter 18 in EP93xx User Guide
memory-mapped device registers
- configuration
- load start/reset value
- read current value
timer counter width: 16 bit vs 32 bit
timer mode: free-running vs. periodic
- periodic can be used for configurable interrupt generation
timer speed: 2 kHz vs. 508 kHz → 508 kHz is recommended
- time horizon = timer counter width / timer speed
debug/watchdog timers: usage optional
here: no time of day needed, no remote synchronization (very hard problem)

Chapter 14 in EP93xx User Guide
- in particular, read "UART Register Descriptions" in Section 14.1
- ignore "Modem Register Descriptions" starting on Page 14-25
character device: 1 byte at a time, asynchronous transmission
memory-mapped device registers
- configuration: speed, byte representation, fifo
  - UART1 = COM1, train control, 2400 baud, 8N2, flow control
  - UART2 = COM2, terminal, 115200 baud, 8N1, no flow control
- RX/TX status
- receive status (discard byte, reset after error)
- data in/out
timing: 2400 baud with 8N2 → 240 bytes/sec
- character in UART vs. character transmitted
- flow control: character transmission vs. reception & processing (details later)
  - A0: where necessary, add short pauses
fifo: throughput vs. latency trade-off - review with interrupts

train speed: 0-14; 15 for reverse (add 16 to turn on lights)
- model trains simulate real-world stopping by gradually slowing down
- we want to preserve this important characteristic
  ⇒ do not directly reverse rolling train!
turnout commands: straight, curved
NOTE: the middle turnouts should always be set to S/C or C/S → avoid C/C, S/S
special command: turn off (last) solenoid
- IMPORTANT: After sending a turnout command, you must wait at least 100ms and at most 500ms. Then, either switch another turnout (which automatically turns off the previous solenoid) or explicitly turn off the last solenoid!
sensors: query some/all
tracks have 5x16 sensors
- set reset mode (single command byte 0xC0)
- read reports after query
- IMPORTANT: track communication is half-duplex, i.e., no control while receiving sensor data

for (;;) {
  while (!c1);
  a1();
  while (!c2);
  a2();
  ...
}