From b73d5fc1af46d739e841af89bf3841fd6a84bdf7 Mon Sep 17 00:00:00 2001
From: Werner Almesberger <werner@almesberger.net>
Date: Wed, 24 Jul 2013 07:57:35 -0300
Subject: [PATCH] atusb/fw/mac.c: remove queued_rx; buffer frames in the MCU
 instead

queued_rx held a frame in the transceiver's receive buffer until we could
transfer it. This may cause frame loss if a new reception begins.

We now retrieve frames from the transceiver immediately and buffer them
in the MCU.
---
 atusb/fw/mac.c | 77 ++++++++++++++++++++++++++++----------------------
 1 file changed, 44 insertions(+), 33 deletions(-)

diff --git a/atusb/fw/mac.c b/atusb/fw/mac.c
index 05d16d6..255ac6e 100644
--- a/atusb/fw/mac.c
+++ b/atusb/fw/mac.c
@@ -22,15 +22,18 @@
 #include "mac.h"
 
 
+#define	RX_BUFS	2
+
+
 bool (*mac_irq)(void) = NULL;
 
 
-static uint8_t rx_buf[MAX_PSDU+2]; /* PHDR+payload+LQ */
+static uint8_t rx_buf[RX_BUFS][MAX_PSDU+2]; /* PHDR+payload+LQ */
+static bool rx_in = 0, rx_out = 0;
 static uint8_t tx_buf[MAX_PSDU];
 static uint8_t tx_size = 0;
 static bool txing = 0;
 static bool queued_tx_ack = 0;
-static bool queued_rx = 0;
 static uint8_t next_seq, this_seq, queued_seq;
 
 
@@ -62,27 +65,45 @@ static void reg_write(uint8_t reg, uint8_t value)
 /* ----- Interrupt handling ------------------------------------------------ */
 
 
-static void receive_frame(void);
+static void rx_done(void *user);
+static void tx_ack_done(void *user);
+
+
+static void usb_next(void)
+{
+	const uint8_t *buf;
+
+	if (rx_in != rx_out) {
+		buf = rx_buf[rx_out];
+		led(1);
+		usb_send(&eps[1], buf, buf[0]+2, rx_done, NULL);
+	}
+
+	if (queued_tx_ack) {
+		usb_send(&eps[1], &queued_seq, 1, tx_ack_done, NULL);
+		queued_tx_ack = 0;	
+	}
+}
+
+
+static void tx_ack_done(void *user)
+{
+	usb_next();
+}
 
 
 static void rx_done(void *user)
 {
 	led(0);
-	if (queued_rx) {
-		receive_frame();
-		queued_rx = 0;
-		return;
-	}
-	if (queued_tx_ack) {
-		usb_send(&eps[1], &queued_seq, 1, rx_done, NULL);
-		queued_tx_ack = 0;	
-	}
+	rx_out = (rx_out+1) & (RX_BUFS-1);
+	usb_next();
 }
 
 
 static void receive_frame(void)
 {
 	uint8_t size, i;
+	uint8_t *buf;
 
 	spi_begin();
 	if (!(spi_io(AT86RF230_BUF_READ) & RX_CRC_VALID)) {
@@ -95,20 +116,16 @@ static void receive_frame(void)
 		return;
 	}
 
-	rx_buf[0] = size;
+	buf = rx_buf[rx_in];
 	for (i = 0; i != size+1; i++)
-		rx_buf[i+1] = spi_recv();
+		buf[i+1] = spi_recv();
 	spi_end();
-	led(1);
-	usb_send(&eps[1], rx_buf, size+2, rx_done, NULL);
-}
 
+	buf[0] = size;
+	rx_in = (rx_in+1) & (RX_BUFS-1);
 
-static void flush_queued_rx(void)
-{
-	if (queued_rx)
-		receive_frame();
-	queued_rx = 0;
+	if (eps[1].state == EP_IDLE)
+		usb_next();
 }
 
 
@@ -122,7 +139,7 @@ static bool handle_irq(void)
 
 	if (txing) {
 		if (eps[1].state == EP_IDLE) {
-			usb_send(&eps[1], &this_seq, 1, rx_done, NULL);
+			usb_send(&eps[1], &this_seq, 1, tx_ack_done, NULL);
 		} else {
 			queued_tx_ack = 1;
 			queued_seq = this_seq;
@@ -131,13 +148,9 @@ static bool handle_irq(void)
 		return 1;
 	}
 
-	/* unlikely */
-	if (eps[1].state != EP_IDLE) {
-		queued_rx = 1;
-		return 1;
-	}
-
-	receive_frame();
+	/* likely */
+	if (eps[1].state == EP_IDLE || rx_in != rx_out)
+		receive_frame();
 
 	return 1;
 }
@@ -193,9 +206,7 @@ static void do_tx(void *user)
 	 */
 	reg_write(REG_TRX_STATE, TRX_CMD_FORCE_PLL_ON);
 
-	flush_queued_rx();
 	handle_irq();
-	queued_rx = 0;
 
 	spi_begin();
 	spi_send(AT86RF230_BUF_WRITE);
@@ -233,7 +244,7 @@ void mac_reset(void)
 	mac_irq = NULL;
 	txing = 0;
 	queued_tx_ack = 0;
-	queued_rx = 0;
+	rx_in = rx_out = 0;
 	next_seq = this_seq = queued_seq = 0;
 
 	/* enable CRC and PHY_RSSI (with RX_CRC_VALID) in SPI status return */