--- /dev/null
+#!/usr/bin/env nickle
+
+/*
+ * Given a main clock frequency,
+ * compute USART clock freq and a table
+ * of USART config parameters for our target baud rates
+ */
+
+real main_clock = 0;
+real usart_clock = 0;
+
+real[] baud_rates = { 4800, 9600, 19200, 57600, 115200 };
+
+void
+compute_baud_rate(real rate) {
+ int divaddval;
+ int mulval;
+
+ real dl_est = usart_clock / (16 * rate);
+
+ if (dl_est == floor(dl_est)) {
+ divaddval = 0;
+ mulval = 1;
+ } else {
+ if (false) {
+
+ /* This is how the docs suggest doing it; this
+ * generates a rate which is reasonably close
+ */
+
+ real fr_est = 1.5;
+
+ /* Compute fractional estimate */
+ do {
+ dl_est = floor(usart_clock / (16 * rate * fr_est) + 0.5);
+ fr_est = usart_clock / (16 * rate * dl_est);
+ } while (fr_est <= 1.1 || 1.9 <= fr_est);
+
+ /* Given fractional estimate, compute divaddval/mulvals that work best */
+
+ real best_dist = 1000;
+ for (int tmp_divaddval = 1; tmp_divaddval < 15; tmp_divaddval++) {
+ for (int tmp_mulval = 1; tmp_mulval < 16; tmp_mulval++) {
+ real fr = 1 + tmp_divaddval / tmp_mulval;
+ real dist = abs(fr - fr_est);
+ if (dist < best_dist) {
+ divaddval = tmp_divaddval;
+ mulval = tmp_mulval;
+ best_dist = dist;
+ }
+ }
+ }
+ } else {
+
+ /* This exhaustively searches for the best match */
+
+ real my_best_dist = 1e20;
+ int my_best_dl;
+ int my_best_divaddval;
+ int my_best_mulval;
+ for (int my_dl = 1; my_dl < 1024; my_dl++) {
+ for (int my_mulval = 1; my_mulval < 16; my_mulval++) {
+ for (int my_divaddval = 0; my_divaddval < my_mulval; my_divaddval++) {
+ real my_rate = usart_clock / ((16 * my_dl) * (1 + my_divaddval/my_mulval));
+
+ real my_dist = abs(rate - my_rate);
+
+ if (my_dist == 0 && my_divaddval == 0) {
+ my_dist = -1;
+ }
+
+ if (my_dist < my_best_dist) {
+ my_best_dl = my_dl;
+ my_best_divaddval = my_divaddval;
+ my_best_mulval = my_mulval;
+ my_best_dist = my_dist;
+ }
+ }
+ }
+ }
+
+ dl_est = my_best_dl;
+ divaddval = my_best_divaddval;
+ mulval = my_best_mulval;
+ }
+ }
+
+ int dl = floor (dl_est);
+
+ real actual = usart_clock / ((16 * dl) * (1 + divaddval/mulval));
+
+ printf("\t[AO_SERIAL_SPEED_%d] = { /* actual = %8.2f */\n", floor(rate), actual);
+ printf("\t\t.dl = %d,\n", dl);
+ printf("\t\t.divaddval = %d,\n", divaddval);
+ printf("\t\t.mulval = %d\n", mulval);
+ printf("\t},\n");
+}
+
+void
+main() {
+ if (dim(argv) < 2) {
+ printf ("usage: %s <main-clock>\n", argv[0]);
+ exit(1);
+ }
+ main_clock = string_to_real(argv[1]);
+
+ for (int div = 0; div < 4; div++) {
+ if (main_clock / (1 << div) <= 12000000) {
+ usart_clock = main_clock / (1 << div);
+ break;
+ }
+ }
+
+ if (usart_clock == 0) {
+ printf ("can't get usart clock in range\n");
+ exit(1);
+ }
+
+ printf ("#define AO_LPC_USARTCLK %d\n\n", floor(usart_clock));
+ printf("static const struct {\n");
+ printf("\tuint16_t dl;\n");
+ printf("\tuint8_t divaddval;\n");
+ printf("\tuint8_t mulval;\n");
+ printf("} ao_usart_speeds[] = {\n");
+ for (int i = 0; i < dim(baud_rates); i++) {
+ compute_baud_rate(baud_rates[i]);
+ }
+ printf ("};\n");
+}
+
+main();