target_flash: Implement blank check

* Reuse flash write buffer for block reads
* Compare against erased value and skip to next sector on mismatch
* Indicate progress via tc_printf() to gdb_if.c or BMDA stdout

src/include/target.h

@@ -70,6 +70,7 @@ bool target_mem_access_needs_halt(target_s *target);
 bool target_flash_erase(target_s *target, target_addr_t addr, size_t len);
 bool target_flash_write(target_s *target, target_addr_t dest, const void *src, size_t len);
 bool target_flash_complete(target_s *target);
+bool target_flash_blank_check(target_s *target);
 
 /* Register access functions */
 size_t target_regs_size(target_s *target);

src/target/target.c

@@ -45,11 +45,13 @@ target_s *target_list = NULL;
 
 static bool target_cmd_mass_erase(target_s *target, int argc, const char **argv);
 static bool target_cmd_range_erase(target_s *target, int argc, const char **argv);
+static bool target_cmd_blank_check(target_s *target, int argc, const char **argv);
 static bool target_cmd_redirect_output(target_s *target, int argc, const char **argv);
 
 const command_s target_cmd_list[] = {
 	{"erase_mass", target_cmd_mass_erase, "Erase whole device Flash"},
 	{"erase_range", target_cmd_range_erase, "Erase a range of memory on a device"},
+	{"blank_check", target_cmd_blank_check, "Blank-check device Flash"},
 	{"redirect_stdout", target_cmd_redirect_output, "Redirect semihosting output to aux USB serial"},
 	{NULL, NULL, NULL},
 };
@@ -510,6 +512,16 @@ static bool target_cmd_range_erase(target_s *const target, const int argc, const
 	return target_flash_erase(target, addr, length);
 }
 
+static bool target_cmd_blank_check(target_s *const target, const int argc, const char **const argv)
+{
+	(void)argc;
+	(void)argv;
+	gdb_out("Blank-checking device Flash: ");
+	const bool result = target_flash_blank_check(target);
+	gdb_out("done\n");
+	return result;
+}
+
 static bool target_cmd_redirect_output(target_s *target, int argc, const char **argv)
 {
 	if (argc == 1) {

src/target/target_flash.c

@@ -312,3 +312,61 @@ bool target_flash_complete(target_s *target)
 	target_exit_flash_mode(target);
 	return result;
 }
+
+static bool flash_blank_check(target_flash_s *flash, target_addr_t src, size_t len, target_addr_t *mismatch)
+{
+	bool result = true; /* Catch false returns with &= */
+	target_s *target = flash->t;
+	platform_timeout_s timeout;
+	platform_timeout_set(&timeout, 500);
+
+	while (len) {
+		const size_t offset = src % flash->writebufsize;
+		const size_t local_len = MIN(flash->writebufsize - offset, len);
+		/* Fetch chunk into sector buffer */
+		target_mem32_read(target, flash->buf, src, local_len);
+
+		/* Compare bytewise with erased value */
+		const uint8_t erased = flash->erased;
+		for (size_t i = 0; i < local_len; i++) {
+			if (flash->buf[i] != erased) {
+				*mismatch = src + i;
+				return false;
+			}
+		}
+		src += local_len;
+		len -= local_len;
+		target_print_progress(&timeout);
+	}
+	return result;
+}
+
+bool target_flash_blank_check(target_s *target)
+{
+	if (!target->flash)
+		return false;
+
+	bool result = true;
+	target_addr_t mismatch = 0;
+
+	for (target_flash_s *flash = target->flash; flash; flash = flash->next) {
+		if (!flash->buf && !flash_buffer_alloc(flash))
+			return false;
+
+		const target_addr_t local_end = flash->start + flash->length;
+		for (target_addr_t local_start = flash->start; local_start < local_end; local_start += flash->blocksize) {
+			result = flash_blank_check(flash, local_start, flash->blocksize, &mismatch);
+			if (!result)
+				tc_printf(target, "Has data at 0x%08" PRIx32 "\n", mismatch);
+			else
+				tc_printf(target, "Blank 0x%08" PRIx32 "+%" PRIu32 "\n", local_start, (uint32_t)flash->blocksize);
+		}
+		/* Free the operation buffer */
+		if (flash->buf) {
+			free(flash->buf);
+			flash->buf = NULL;
+		}
+	}
+
+	return result;
+}