#!/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();