cm-5 mode5 revision 5 (newer one in older gists)

mode5.c

/* http://www.housedillon.com/?p=1272
 * Written by iskunk (Daniel Richard G.)
 * THIS FILE IS IN THE PUBLIC DOMAIN
 *
 * Program to emulate the CM-5's "random and pleasing" LED panel mode
 * (revision 5, "House Dillon video exclusive" edition)
 */

#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <unistd.h>
#include <assert.h>

#define NUM_ROWS 32		/* unique rows */
#define NUM_ROWS_DISPLAYED 106	/* rows in front panel display */

/* Dillon's video shows a single 16x32 panel */
#undef NUM_ROWS_DISPLAYED
#define NUM_ROWS_DISPLAYED 32

#ifndef NDEBUG
# define COMPARE_8741
#endif

#define RNUM_SEED 0xBAD

static uint16_t rnum = RNUM_SEED;
static uint16_t rnum_8741 = RNUM_SEED;

/* Note: rows[0] is the top row; most significant bit is at left;
 * a zero bit corresponds to a lit LED
 */
static uint16_t rows[NUM_ROWS];

/* The source of this pattern is not [yet] known. Note that all these rows
 * will be shifted by one bit before being displayed.
 */
static const uint16_t rows_mystery[NUM_ROWS] = {
	0x8F10, 0x9112, 0x9314, 0x9516, 0x18E9, 0x5899, 0x38D9, 0x78B9,
	0x9F20, 0xA122, 0xA324, 0xA526, 0x14E5, 0x5495, 0x34D5, 0x74B5,
	0xAF30, 0xB132, 0xB334, 0xB536, 0x1CED, 0x5C9D, 0x3CDD, 0x7CBD,
	0xBF40, 0xC142, 0xC344, 0xC546, 0x12E3, 0x5293, 0x32D3, 0x72B3
};

static uint16_t get_random_bit(void)
{
#define X rnum

	/* https://en.wikipedia.org/wiki/Linear_feedback_shift_register
	 * Primitive polynomial: x^16 + x^15 + x^13 + x^4 + 1
	 */
	uint16_t lfsr_bit = ((X >> 0) ^ (X >> 1) ^ (X >> 3) ^ (X >> 12)) & 1;

	uint16_t rand_bit = (X | (X >> 2)) & 1;

#undef X

	rnum = (lfsr_bit << 15) | (rnum >> 1);

	return rand_bit;
}

/* This is a rough translation of Jim's Intel 8741 assembler code into C
 */
static uint16_t get_random_bit_8741(void)
{
	uint8_t RNUM   = rnum_8741 & 0xFF;	/* low-order byte */
	uint8_t RNUMp1 = rnum_8741 >> 8;	/* high-order byte */
	uint8_t A, C, tmp;

#define b(var, n) ((var >> n) & 1)	/* gets Nth bit */
#define cpl(flag) flag = flag ^ 1
#define jnb(val, label) if (!val) goto label
#define orl(flag, val) flag |= val
#define rrc(reg) tmp = reg & 1; reg = (C << 7) | (reg >> 1); C = tmp

	/* ;This subroutine implements a 16 bit random number generator based
	 * ;on the primitive polynomial:
	 * ;
	 * ;	1 + X + X^3 + X^12 + X^16
	 * ;
	 * ;The value is stored in memory as RNUM.  This subroutine returns
	 * ;with the low order byte of the RNUM in the accumulator and a random
	 * ;bit value in the Carry (C) bit.
	 * ;
	 */
	C = b(RNUM,0);		/* mov C, RNUM.0	;get the units value of the PP		*/
	jnb(b(RNUM,1), rand1);	/* jnb RNUM.1, rand1	;jmp if X = 0				*/
	cpl(C);			/* cpl C		;else compliment C (xor)		*/
rand1:	jnb(b(RNUM,3), rand2);	/* jnb RNUM.3, rand2	;jmp if X^3 = 0				*/
	cpl(C);			/* cpl C		;else compliment C (xor)		*/
rand2:	jnb(b(RNUMp1,4), rand3);  /* jnb (RNUM+1).4, rand3  ;jmp if X^12 = 0			*/
	cpl(C);			/* cpl C		;else compliment C (xor)		*/
rand3:	A = RNUMp1;		/* mov A, RNUM+1	;get high byte of RNUM			*/
	rrc(A);			/* rrc A		;and rotate down (thru accumulator)	*/
	RNUMp1 = A;		/* mov RNUM+1, A	;save it back to memory			*/
	A = RNUM;		/* mov A, RNUM		;get low byte of RNUM			*/
	rrc(A);			/* rrc A		;and rotate down (thru accumulator)	*/
	RNUM = A;		/* mov RNUM, A		;save it back to memory			*/
	orl(C, b(RNUM,1));	/* orl C, RNUM.1	;light LED only 25 percent of the time	*/
				/* ret			;return					*/

#undef b
#undef cpl
#undef jnb
#undef orl
#undef rrc

	rnum_8741 = RNUM | (RNUMp1 << 8);

	return C;
}

static void print_row(uint16_t x)
{
	uint16_t m;
	int pos;
	char v[17];

	/* 0 -> LED on, 1 -> LED off */
	for (m = 1 << 15, pos = 0; m != 0; m >>= 1, pos++)
		v[pos] = (x & m) ? '-' : 'O';

	v[16] = '\0';

	puts(v);
}

static void print_panel(void)
{
	int i;

	/* ANSI sequence to clear terminal */
	fputs("\033[2J\033[1;1H", stdout);

	for (i = 0; i < NUM_ROWS_DISPLAYED; i++)
		print_row(rows[i & 31]);
}

int main(void)
{
	int i;
	int t = 2;

	/* Initial state: all but 3 LEDs lit */
	memset(rows, 0, sizeof(rows));
	rows[0] = 0x9400;
	print_panel();
	fflush(stdout);
	usleep(600000); /* 600 ms */

	/* Initialize rows with mystery pattern */
	memcpy(rows, rows_mystery, sizeof(rows));

	for (;;)
	{
		for (i = NUM_ROWS - 1; i >= 0; i--)
		{
			uint16_t bit = get_random_bit();

#ifdef COMPARE_8741
			uint16_t bit_8741 = get_random_bit_8741();
			assert(bit == bit_8741);
			assert(rnum == rnum_8741);
#endif

			if (i & 4)
				rows[i] = (bit << 15) | (rows[i] >> 1);
			else
				rows[i] = (rows[i] << 1) | bit;
		}

		print_panel();

		/* Print timestamp for matching to Dillon's video */
		if (++t < 300)
			printf("\n00:00:%02d:%02d\n", t / 5, 6 * (t % 5));

		fflush(stdout);
		usleep(200000); /* 200 ms */
	}

	return 0;
}

/* EOF */