strix/arduino/strix_capture/strix_capture.ino

// STRIX raw capture tool: boots the STRIX FPGA image and gives the host (tools/jitter.py)
// register access and raw captures over USB serial.
//
// Commands (one per line, numbers in decimal):
//   id                    print the FPGA identification
//   r <register>          read a register, prints its value
//   w <register> <value>  write a register, prints "OK"
//   cap                   start a capture with the current settings and send it as
//                         "DATA <n>\n" followed by n raw bytes

#include <SPI.h>
#include <VidorBoot.h>
#include "wiring_private.h"

// STRIX SPI link: SERCOM0 on its alternate pins A3 MOSI (PAD0), A4 SCK (PAD1), A6 MISO (PAD3).
SPIClassSAMD strixSpi(&sercom0, A6, A4, A3, SPI_PAD_0_SCK_1, SERCOM_RX_PAD_3);
const int STRIX_SS = A5;
const SPISettings STRIX_SPI_SETTINGS(8000000, MSBFIRST, SPI_MODE0);

enum : uint8_t {
  REG_ID0 = 0x00,
  REG_VERSION = 0x04,
  REG_CONTROL = 0x0B,
  REG_STATUS = 0x0C,
  REG_DATA = 0x10,
};

const uint8_t READ = 0x80;
const uint8_t CONTROL_START_CAPTURE = 0x01;
const uint8_t STATUS_CAPTURE_DONE = 0x02;
const size_t CAPTURE_BYTES = 32768;
const size_t CHUNK_BYTES = 512;

VidorUtils fpga;

void beginTransaction(uint8_t command) {
  strixSpi.beginTransaction(STRIX_SPI_SETTINGS);
  digitalWrite(STRIX_SS, LOW);
  strixSpi.transfer(command);
}

void endTransaction() {
  digitalWrite(STRIX_SS, HIGH);
  strixSpi.endTransaction();
}

void writeRegister(uint8_t reg, uint8_t value) {
  beginTransaction(reg);
  strixSpi.transfer(value);
  endTransaction();
}

uint8_t readRegister(uint8_t reg) {
  beginTransaction(READ | reg);
  uint8_t value = strixSpi.transfer(0);
  endTransaction();
  return value;
}

void printId() {
  char id[5] = {0};
  for (uint8_t i = 0; i < 4; i++) id[i] = readRegister(REG_ID0 + i);
  Serial.print(id);
  Serial.print(" v");
  Serial.println(readRegister(REG_VERSION));
}

void capture() {
  writeRegister(REG_CONTROL, CONTROL_START_CAPTURE);

  // 262,144 samples at 120 MHz take up to 143 s at the maximum decimation of 65535.
  unsigned long start = millis();
  while (!(readRegister(REG_STATUS) & STATUS_CAPTURE_DONE)) {
    if (millis() - start > 180000) {
      Serial.println("ERR timeout");
      return;
    }
  }

  Serial.print("DATA ");
  Serial.println(CAPTURE_BYTES);

  static uint8_t chunk[CHUNK_BYTES];
  for (size_t sent = 0; sent < CAPTURE_BYTES; sent += CHUNK_BYTES) {
    beginTransaction(READ | REG_DATA);
    for (size_t i = 0; i < CHUNK_BYTES; i++) chunk[i] = strixSpi.transfer(0);
    endTransaction();
    Serial.write(chunk, CHUNK_BYTES);
  }
}

// Parses "<a>" or "<a> <b>" after the command word; returns the number of values found.
int parseArgs(const String &args, long &a, long &b) {
  int space = args.indexOf(' ');
  if (args.length() == 0) return 0;
  a = args.substring(0, space < 0 ? args.length() : space).toInt();
  if (space < 0) return 1;
  b = args.substring(space + 1).toInt();
  return 2;
}

void handleCommand(String line) {
  line.trim();
  int space = line.indexOf(' ');
  String command = space < 0 ? line : line.substring(0, space);
  String args = space < 0 ? "" : line.substring(space + 1);
  long reg = 0, value = 0;
  int count = parseArgs(args, reg, value);

  if (command == "id") {
    printId();
  } else if (command == "r" && count == 1 && reg >= 0 && reg < 0x80) {
    Serial.println(readRegister(reg));
  } else if (command == "w" && count == 2 && reg >= 0 && reg < 0x80 && value >= 0 && value < 256) {
    writeRegister(reg, value);
    Serial.println("OK");
  } else if (command == "cap") {
    capture();
  } else if (line.length() > 0) {
    Serial.println("ERR unknown or malformed command");
  }
}

void setup() {
  Serial.begin(115200);
  while (!Serial);

  // Starts the 48 MHz FPGA clock and switches the FPGA from Arduino's loader to our image.
  if (!fpga.begin(true)) {
    Serial.println("ERR FPGA boot failed");
  }
  delay(100);  // configuration and PLL lock

  pinMode(STRIX_SS, OUTPUT);
  digitalWrite(STRIX_SS, HIGH);
  strixSpi.begin();
  // SPIClassSAMD::begin() applies the pins' default mux; A3-A6 need SERCOM0's alternate mux.
  pinPeripheral(A3, PIO_SERCOM_ALT);
  pinPeripheral(A4, PIO_SERCOM_ALT);
  pinPeripheral(A6, PIO_SERCOM_ALT);

  printId();
}

void loop() {
  if (Serial.available()) handleCommand(Serial.readStringUntil('\n'));
}