atusb/fw/: added free-running 48 bit 8 MHz counter for clock measurements

- atusb.c (main): poll the 16 bit timer for overflows
- board.h (timer_poll, timer_read), (board.c (timer_h, timer_poll,
  timer_read, board_init): added support for a free-running 48 bit timer
  (16 bits in hardware, 32 bits in software)
- include/atusb/ep0.h (ATUSB_TIMER), ep0.c (my_setup): new request
  ATUSB_TIMER to retrieve the value of the 8 MHz counter
- include/atusb/ep0.h (enum atspi_requests): describe what the groups
  of requests do

atusb/fw/atusb.c

@@ -36,6 +36,8 @@ int main(void)
 	usb_init();
 	ep0_init();
 
-	while (1)
+	while (1) {
 		usb_poll();
+		timer_poll();
+	}
 }

atusb/fw/board.c

@@ -29,6 +29,9 @@
 uint8_t board_sernum[42] = { 42, USB_DT_STRING };
 
 
+static uint32_t timer_h = 0;	/* 2^(16+32) / 8 MHz = ~1.1 years */
+
+
 static void set_clkm(void)
 {
 	/* switch CLKM to 8 MHz */
@@ -99,6 +102,36 @@ void panic(void)
 }
 
 
+void timer_poll(void)
+{
+	if (!(TIFR1 & (1 << TOV1)))
+		return;
+	TIFR1 = 1 << TOV1;
+	timer_h++;
+}
+
+
+uint64_t timer_read(void)
+{
+	uint32_t high;
+	uint8_t low, mid;
+
+	do {
+		timer_poll();
+		high = timer_h;
+		low = TCNT1L;
+		mid = TCNT1H;
+	}
+	while (TIFR1 & (1 << TOV1));
+
+	/*
+	 * We need all these casts because the intermediate results are handled
+	 * as if they were signed and thus get sign-expanded. Sounds wrong-ish.
+	 */
+	return (uint64_t) high << 16 | (uint64_t) mid << 8 | (uint64_t) low;
+}
+
+
 static char hex(uint8_t nibble)
 {
 	return nibble < 10 ? '0'+nibble : 'a'+nibble-10;
@@ -138,5 +171,10 @@ void board_init(void)
 	OUT(nRST_RF);   /* this also resets the transceiver */
 	OUT(SLP_TR);
 
+	/* configure timer 1 as a free-running CLK counter */
+
+	TCCR1A = 0;
+	TCCR1B = 1 << CS10;
+
 	get_sernum();
 }

atusb/fw/board.h

@@ -74,6 +74,9 @@ uint8_t read_irq(void);
 void led(int on);
 void panic(void);
 
+void timer_poll(void);
+uint64_t timer_read(void);
+
 void board_init(void);
 
 #endif /* !BOARD_H */

atusb/fw/ep0.c

@@ -12,6 +12,7 @@
 
 
 #include <stdint.h>
+#include <string.h>
 
 #include <avr/io.h>
 
@@ -57,6 +58,7 @@ static int my_setup(const struct setup_request *setup)
 {
 	unsigned tmp;
 	uint8_t i;
+	uint64_t tmp64;
 
 	switch (setup->bmRequestType | setup->bRequest << 8) {
 	case ATUSB_FROM_DEV(ATUSB_ID):
@@ -101,6 +103,16 @@ static int my_setup(const struct setup_request *setup)
 		usb_send(&eps[0], buf, 1, NULL, NULL);
 		return 1;
 
+	case ATUSB_FROM_DEV(ATUSB_TIMER):
+		debug("ATUSB_TIMER\n");
+		size = setup->wLength;
+		if (size > sizeof(tmp64))
+			size = sizeof(tmp64);
+		tmp64 = timer_read();
+		memcpy(buf, &tmp64, sizeof(tmp64));
+		usb_send(&eps[0], buf, size, NULL, NULL);
+		return 1;
+
 	case ATUSB_TO_DEV(ATUSB_REG_WRITE):
 		debug("ATUSB_REG_WRITE\n");
 		spi_begin();

atusb/fw/include/atusb/ep0.h

@@ -24,6 +24,7 @@
  * host->	ATUSB_RF_RESET		-		-	0
  * ->host	ATUSB_POLL_INT		-		-	1
  * host->	ATUSB_TEST		-		-	0
+ * ->host	ATUSB_TIMER		-		-	#bytes (6)
  *
  * host->	ATUSB_REG_WRITE		value		addr	0
  * ->host	ATUSB_REG_READ		-		addr	1
@@ -64,13 +65,14 @@
 
 
 enum atspi_requests {
-	ATUSB_ID			= 0x00,
+	ATUSB_ID			= 0x00,	/* system status/control grp */
 	ATUSB_BUILD,
 	ATUSB_RESET,
-	ATUSB_RF_RESET			= 0x10,
+	ATUSB_RF_RESET			= 0x10,	/* debug/test group */
 	ATUSB_POLL_INT,
-	ATUSB_TEST,
-	ATUSB_REG_WRITE			= 0x20,
+	ATUSB_TEST,			/* atusb-sil only */
+	ATUSB_TIMER,
+	ATUSB_REG_WRITE			= 0x20,	/* transceiver group */
 	ATUSB_REG_READ,
 	ATUSB_BUF_WRITE,
 	ATUSB_BUF_READ,