From ebdc38fc91d6d0855671128c7b958bd75937eb73 Mon Sep 17 00:00:00 2001
From: Feliks <feliks.montez@gmail.com>
Date: Mon, 23 Mar 2020 23:04:36 -0400
Subject: [PATCH] flush rx buffer when bad crc and fix frame payload length

---
 litex/soc/software/bios/boot.c | 15 ++++++++++-----
 litex/soc/software/bios/sfl.h  |  2 +-
 litex/tools/litex_term.py      |  4 ++--
 3 files changed, 13 insertions(+), 8 deletions(-)

diff --git a/litex/soc/software/bios/boot.c b/litex/soc/software/bios/boot.c
index 41230ec36..62c83e307 100644
--- a/litex/soc/software/bios/boot.c
+++ b/litex/soc/software/bios/boot.c
@@ -122,6 +122,7 @@ int serialboot(void)
 	printf("Booting from serial...\n");
 	printf("Press Q or ESC to abort boot completely.\n");
 
+	// send the "magic" request to host for a firmware download
 	c = str;
 	while(*c) {
 		uart_write(*c);
@@ -145,18 +146,22 @@ int serialboot(void)
 		int goodcrc;
 
 		/* Get one Frame */
-		frame.length = uart_read();
+		frame.payload_length = uart_read();
 		frame.crc[0] = uart_read();
 		frame.crc[1] = uart_read();
 		frame.cmd = uart_read();
-		for(i=0;i<frame.length;i++)
+		for(i=0;i<frame.payload_length;i++)
 			frame.payload[i] = uart_read();
 
 		/* Check Frame CRC (if CMD has a CRC) */
 		if (frame.cmd != SFL_CMD_LOAD_NO_CRC) {
 			actualcrc = ((int)frame.crc[0] << 8)|(int)frame.crc[1];
-			goodcrc = crc16(&frame.cmd, frame.length+1);
+			goodcrc = crc16(&frame.cmd, frame.payload_length+1);
 			if(actualcrc != goodcrc) {
+				// clear out the RX buffer
+				while (uart_read_nonblock()) {
+					uart_read();
+				}
 				failed++;
 				if(failed == MAX_FAILED) {
 					printf("Too many consecutive errors, aborting");
@@ -179,7 +184,7 @@ int serialboot(void)
 
 				failed = 0;
 				writepointer = (char *) get_uint32(&frame.payload[0]);
-				for(i=4;i<frame.length;i++)
+				for(i=4;i<frame.payload_length;i++)
 					*(writepointer++) = frame.payload[i];
 				if (frame.cmd == SFL_CMD_LOAD)
 					uart_write(SFL_ACK_SUCCESS);
@@ -201,7 +206,7 @@ int serialboot(void)
 				failed = 0;
 				addr = get_uint32(&frame.payload[0]);
 
-				for (i = 4; i < frame.length; i++) {
+				for (i = 4; i < frame.payload_length; i++) {
 					// erase page at sector boundaries before writing
 					if ((addr & (SPIFLASH_SECTOR_SIZE - 1)) == 0) {
 						erase_flash_sector(addr);
diff --git a/litex/soc/software/bios/sfl.h b/litex/soc/software/bios/sfl.h
index cca67f6f1..b09aee485 100644
--- a/litex/soc/software/bios/sfl.h
+++ b/litex/soc/software/bios/sfl.h
@@ -9,7 +9,7 @@
 #define SFL_MAGIC_ACK "z6IHG7cYDID6o\n"
 
 struct sfl_frame {
-	unsigned char length;
+	unsigned char payload_length;
 	unsigned char crc[2];
 	unsigned char cmd;
 	unsigned char payload[255];
diff --git a/litex/tools/litex_term.py b/litex/tools/litex_term.py
index a71245d4c..107dee630 100755
--- a/litex/tools/litex_term.py
+++ b/litex/tools/litex_term.py
@@ -52,7 +52,7 @@ sfl_prompt_ack = b"\x06"
 sfl_magic_req = b"sL5DdSMmkekro\n"
 sfl_magic_ack = b"z6IHG7cYDID6o\n"
 
-sfl_payload_length = 251
+sfl_payload_length = 64#251
 
 # General commands
 sfl_cmd_abort       = b"\x00"
@@ -212,7 +212,7 @@ class LiteXTerm:
                                                     100*position//length))
             sys.stdout.flush()
             frame = SFLFrame()
-            frame_data = f.read(min(remaining, sfl_payload_length))
+            frame_data = f.read(min(remaining, sfl_payload_length-4))
             if self.flash:
                 frame.cmd = sfl_cmd_flash
             else: