From f4ff8f76309d82773881a24cad9d13116ce36025 Mon Sep 17 00:00:00 2001
From: Piotr Esden-Tempski <piotr@esden.net>
Date: Sat, 18 Aug 2018 15:26:37 -0700
Subject: Improved JEDEC ID read function.

The function now checks how long the extended JEDEC ID field is for the
particular FLASH chip and only reads the amount provided by the chip.
---
 iceprog/iceprog.c | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/iceprog/iceprog.c b/iceprog/iceprog.c
index ca3ce48..42abd86 100644
--- a/iceprog/iceprog.c
+++ b/iceprog/iceprog.c
@@ -322,16 +322,42 @@ static void sram_chip_select(bool assert)
 
 static void flash_read_id()
 {
-	// fprintf(stderr, "read flash ID..\n");
+	/* JEDEC ID structure:
+	 * Byte No. | Data Type
+	 * ---------+----------
+	 *        0 | FC_JEDECID Request Command
+	 *        1 | MFG ID
+	 *        2 | Dev ID 1
+	 *        3 | Dev ID 2
+	 *        4 | Ext Dev Str Len
+	 */
 
-	uint8_t data[21] = { FC_JEDECID };
+	uint8_t data[260] = { FC_JEDECID };
+	int len = 5; // command + 4 response bytes
+
+	if (verbose) fprintf(stderr, "read flash ID..\n");
 
 	flash_chip_select(true);
-	xfer_spi(data, 21);
+
+	// Write command and read first 4 bytes
+	xfer_spi(data, len);
+
+	if(data[4] == 0xFF)
+		fprintf(stderr, "Extended Device String Length is 0xFF, "
+				"this is likely a read error. Ignorig...\n");
+	else {
+		// Read extended JEDEC ID bytes
+		if(data[4] != 0) {
+			len += data[4];
+			xfer_spi(data + 5, len - 5);
+		}
+	}
+
 	flash_chip_select(false);
 
+	// TODO: Add full decode of the JEDEC ID.
 	fprintf(stderr, "flash ID:");
-	for (int i = 1; i < 21; i++)
+	for (int i = 1; i < len; i++)
 		fprintf(stderr, " 0x%02X", data[i]);
 	fprintf(stderr, "\n");
 }
-- 
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