- * Now that the firmware is "transformed", we will transcribe the
- * firmware blob into a sequence of toggles of the Dx wires. This
- * sequence will be fed directly into the Sigma, which must be in
- * the FPGA bitbang programming mode.
+ * Generate a sequence of bitbang samples. With two samples per
+ * FPGA configuration bit, providing the level for the DIN signal
+ * as well as two edges for CCLK. See Xilinx UG332 for details
+ * ("slave serial" mode).
+ *
+ * Note that CCLK is inverted in hardware. That's why the
+ * respective bit is first set and then cleared in the bitbang
+ * sample sets. So that the DIN level will be stable when the
+ * data gets sampled at the rising CCLK edge, and the signals'
+ * setup time constraint will be met.
+ *
+ * The caller will put the FPGA into download mode, will send
+ * the bitbang samples, and release the allocated memory.