/*-------------------------------------------

receive.c
contains code that will receive data from a board
that contains the send.c code

data flow is as follows:
send port			receive port
data (0..3)	<-->	data (0..3)
ack_img(4)	-->		ack_img(4)
ack_ram(5)	-->		ack_ram(5)
req_img(6)	<--		req_img(6)
req_ram(7)	<--		req_ram(7)


--------------------------------------------*/

#include <90s8515.h>
#include <delay.h> 

#define RECEIVE_PORT	PORTA  
#define RECEIVE_PIN		PINA
#define RECEIVE_DIR		DDRA

#define ACK_IMG			RECEIVE_PIN.4
#define ACK_RAM			RECEIVE_PIN.5

#define REQ_IMG			RECEIVE_PORT.6
#define REQ_RAM			RECEIVE_PORT.7

#define AND_MASK		0x0f

#define TRUE			1
#define FALSE			0

// receive_init() MUST be called before receive is ever called              
void receive_init(){
	RECEIVE_PORT = 0x00;			// clear the receive port, no pull-ups
	RECEIVE_DIR = 0xc0;				// control pins are output

	delay_ms(100);					// delay for other board to turn on
}

unsigned char receive_nibble(){
	unsigned char ret;

	REQ_IMG = TRUE;
	while(ACK_IMG == FALSE){}		// wait for data to become ready
	
	ret = RECEIVE_PIN & AND_MASK;	// get the data
	REQ_IMG = FALSE;				// signal that transfer is complete
	
	while(ACK_IMG == TRUE){}		// wait for other board to reset
	
	return ret;
}

// receive() is a blocking call
unsigned char receive(){
	unsigned char ret;

	ret = receive_nibble();
	return ((ret << 4) & 0xf0) | receive_nibble();
}



unsigned char retrieve_nibble(){
	unsigned char ret;

	REQ_RAM = TRUE;
	while(ACK_RAM == FALSE){}		// wait for data to become ready
	
	ret = RECEIVE_PIN & AND_MASK;	// get the data
	REQ_RAM = FALSE;				// signal that transfer is complete
	
	while(ACK_RAM == TRUE){}		// wait for other board to reset
	
	return ret;
}

// retrieve() is a blocking call
unsigned char retrieve(){
	unsigned char ret;

	ret = retrieve_nibble();
	return ((ret << 4) & 0xf0) | retrieve_nibble();
}



void store_nibble(unsigned char data){
	RECEIVE_PORT = data & AND_MASK;

	REQ_RAM = TRUE;					// request data storage
	while(ACK_RAM == FALSE){}		// wait for ack

	REQ_RAM = FALSE;				// drop the request
	while(ACK_RAM == TRUE){}		// wait for ack to drop
}

void store(unsigned char data){
	RECEIVE_DIR = 0xcf;
	store_nibble(data >> 4);
	store_nibble(data);
	RECEIVE_DIR = 0xc0;
}