The Arduino wasn't fast enough for the Amstrad CPC Printer port. Crazy, isn't it?
There's a couple of reasons for it. While the CPC may not be sending characters particularly fast, there's only a very small window after Strobe is pulsed that the data is still valid. And entering an interrupt has a minimum delay, which is roughly 1ms. If the CPC changes the value too quickly then you can't capture it in a naive manner and would need some extra hardware support such as an external 8-way latch.
Also, GPIO's are arranged into groups of 8, and each is read as a whole byte. But since you're manually reading each bit individually you're really reading each pin many times but discarding the results, which makes the whole process take much longer in the critical period.
You currently have the data lines split across ports B and D, so instead you can just read each port once and then do the bit manipulation to extract the actual data byte afterwards, which will make it much easier to keep up with the CPC (partly because you eliminate 6 unnecessary port reads entirely, and partly because you move all the calculations out of the critical section.)
I rewrote the arduino side quickly, code is below. It adds software debouncing in the main loop (rather than using interrupts) and changed the serial writes to send the raw bytes instead of unnecessarily converting to hex ascii, although that also requires updating the python code. Also the select/deselect codes are 17 and 19 decimal, not hex!
(edit: fixed minor bug in debounce, it's not like I tested this or anything...)
#define PRN_STRB 5 // /Strobe
#define ONOFF_BTN 6 // Online/Offline signal (through push-buttons + 555 Timer IC)
#define PRN_D0 0 // Data 0
#define PRN_D1 1 // Data 1
#define PRN_D2 2 // Data 2
#define PRN_D3 3 // Data 3
#define PRN_D4 4 // Data 4
#define PRN_D5 7 // Data 5
#define PRN_D6 8 // Data 6
#define PRN_BUSY 9 // Busy = HIGH / Ready = LOW
#define ONOFF_LED 10 // Indicator of "printer" Online/Offline
#define COM_SPEED 115200 // Speed of the COM port between Arduino and PC
#define DEBOUNCE_LIMIT 10 // button input must be stable for this many reads to register
/////////////////////////////////////////////////////////////////////////
byte data = 0; // Variable for converting parallel data from D0..D6 as a single byte
bool wasOnline = false; // Variable for storing Online/Offline push-button state
byte debounce_count = 0;
/////////////////////////////////////////////////////////////////////////
void setup() {
pinMode(PRN_BUSY, OUTPUT);
digitalWrite(PRN_BUSY, 1); // Tell CPC that we're busy setting up everything
pinMode(ONOFF_LED, OUTPUT);
digitalWrite(ONOFF_LED, LOW);
pinMode(PRN_D0, INPUT);
pinMode(PRN_D1, INPUT);
pinMode(PRN_D2, INPUT);
pinMode(PRN_D3, INPUT);
pinMode(PRN_D4, INPUT);
pinMode(PRN_D5, INPUT);
pinMode(PRN_D6, INPUT);
pinMode(PRN_STRB, INPUT_PULLUP);
attachInterrupt(digitalPinToInterrupt(PRN_STRB), readCPCbyte, LOW);
digitalWrite(11, HIGH); // turn the Teensy's internal LED on
Serial.begin(COM_SPEED);
Serial.write(19); // 19 = Deselect printer
}
void readCPCbyte(){
// This function is called when /Strobe is Low (detected by Arduino interrupt)
// read the ports as fast as possible
// PINx returns the current input of port x
byte port_b = PINB;
byte port_d = PIND;
// below just needs to happen before the next Strobe
// reassemble data byte
// (0) D3 D2 B7 B3 B2 B1 B0
data = ((port_d & 0b00001100) << 3) | ((port_b & 0b1000000) >> 3) | (port_b & 0b00001111);
// print byte to the Serial port
Serial.write(buf);
}
void loop()
{
// debounce the online button and toggle busy status when pressed
if (!digitalRead(ONOFF_BTN))
{
if (debounce_count < DEBOUNCE_LIMIT)
{
debounce_count++;
}
else
{
if (wasOnline)
{
wasOnline = false;
Serial.write(19); // 19 = Deselect printer
digitalWrite(PRN_BUSY, HIGH); // Printer is Offline
}
else
{
wasOnline = true;
Serial.write(17); // 17 = Select printer
digitalWrite(PRN_BUSY, LOW); // Printer is Online, tell the CPC that we're ready for data
}
digitalWrite(ONOFF_LED, wasOnline);
}
}
else
{
debounce_count = 0;
}
}
Topic: ACPCPE - Amstrad CPC Printer Emulator (DIY) (Read 430 times)