X-Git-Url: http://git.mutantstargoat.com/user/nuclear/?p=romdev;a=blobdiff_plain;f=fw%2Fsrc%2Fmain.c;h=1d248f29e9acfc12272e0f155131f096c48ec9b7;hp=c07b34e99258d3fd7fe3ea032c32369f6bf10e96;hb=a8c29255c8b1aefb89a67ea777ad06ad5ea42676;hpb=0d51712984ed7c2f32e29e325f93dd5d97fa3ce0

diff --git a/fw/src/main.c b/fw/src/main.c
index c07b34e..1d248f2 100644
--- a/fw/src/main.c
+++ b/fw/src/main.c
@@ -34,6 +34,7 @@ static void end_prog(void);
 static void write_ram(uint16_t addr, uint8_t val);
 static uint8_t read_ram(uint16_t addr);
 static void set_data_bus(unsigned char val);
+static void release_data_bus(void);
 static void set_addr_bus(uint16_t addr);
 static void sys_reset(void);
 static inline void iodelay(void);
@@ -48,12 +49,12 @@ static unsigned char inp_cidx;
 
 int main(void)
 {
-	/* SPI (SS/MOSI/SCK) are outputs, as are the low 2 data bus bits */
-	DDRB = PB_SS | PB_MOSI | PB_SCK | 3;
+	/* SPI (SS/MOSI/SCK) are outputs */
+	DDRB = PB_SS | PB_MOSI | PB_SCK;
 	PORTB = PB_SS;	/* drive SS high when not in programming mode */
 	DDRC = 0xff;	/* control signals are all outputs */
 	PORTC = PC_CS | PC_WE | PC_OE | PC_SYSRST;
-	DDRD = 0xff;	/* always drive the (high bits of the) data bus */
+	DDRD = 0;	/* tri-state the data bus by default (high 6 bits, low 2 are in DDRB) */
 	PORTD = 0;
 
 	/* disable all pullups */
@@ -184,6 +185,7 @@ static void write_ram(uint16_t addr, uint8_t val)
 	iodelay();
 	PORTC |= PC_CS;
 	PORTC |= PC_WE;
+	release_data_bus();
 }
 
 static uint8_t read_ram(uint16_t addr)
@@ -193,15 +195,24 @@ static uint8_t read_ram(uint16_t addr)
 	PORTC |= PC_WE;
 	PORTC &= ~(PC_CS | PC_OE);
 	iodelay();
-	val = (PORTD & 0xfe) | (PORTB & 3);
+	val = (PIND & 0xfc) | (PINB & 3);
 	PORTC |= PC_CS | PC_OE;
 	return val;
 }
 
 static void set_data_bus(unsigned char val)
 {
-	PORTB = (PORTB & 0xfe) | (val & 3);
-	PORTC = val;
+	/* drive the data bus */
+	DDRD = 0xff;
+	DDRB |= 3;
+	PORTB = (PORTB & 0xfc) | (val & 3);
+	PORTD = val;
+}
+
+static void release_data_bus(void)
+{
+	DDRD = 0;
+	DDRB &= 0xfc;
 }
 
 static void set_addr_bus(uint16_t addr)