diff --git a/src/butterfly.c b/src/butterfly.c
index f61a02b9..e9f97a7f 100644
--- a/src/butterfly.c
+++ b/src/butterfly.c
@@ -84,8 +84,8 @@ static void butterfly_teardown(PROGRAMMER *pgm) {
   pgm->cookie = NULL;
 }
 
-static int butterfly_send(const PROGRAMMER *pgm, char *buf, size_t len) {
-  return serial_send(&pgm->fd, (unsigned char *) buf, len);
+static int butterfly_send(const PROGRAMMER *pgm, const char *buf, size_t len) {
+  return serial_send(&pgm->fd, (const unsigned char *) buf, len);
 }
 
 static int butterfly_recv(const PROGRAMMER *pgm, char *buf, size_t len) {
@@ -174,11 +174,11 @@ static int butterfly_initialize(const PROGRAMMER *pgm, const AVRPART *p) {
    */
   msg_notice("connecting to programmer: ");
   if(pgm->flag & IS_BUTTERFLY_MK) {
-    char mk_reset_cmd[6] = { "#aR@S\r" };
+    const char * const mk_reset_cmd = "#aR@S\r";
     unsigned char mk_timeout = 0;
 
     msg_notice(".");
-    EI(butterfly_send(pgm, mk_reset_cmd, sizeof(mk_reset_cmd)));
+    EI(butterfly_send(pgm, mk_reset_cmd, strlen(mk_reset_cmd)));
     usleep(20000);
 
     do {
diff --git a/src/ft245r.c b/src/ft245r.c
index 873651cd..2cf7eff3 100644
--- a/src/ft245r.c
+++ b/src/ft245r.c
@@ -253,7 +253,7 @@ static int ft245r_flush(const PROGRAMMER *pgm) {
     len -= avail;
     my.rx.pending += avail;
   }
-  my.tx.len = 0;
+
   return 0;
 }
 
@@ -263,8 +263,10 @@ static int ft245r_send2(const PROGRAMMER *pgm, unsigned char *buf, size_t len, b
       if(discard_rx_data)
         ++my.rx.discard;
       my.tx.buf[my.tx.len++] = buf[i];
-      if(my.tx.len >= FT245R_MIN_FIFO_SIZE)
+      if(my.tx.len >= FT245R_MIN_FIFO_SIZE) {
         ft245r_flush(pgm);
+        my.tx.len = 0;
+      }
     }
   }
   return 0;
@@ -280,6 +282,7 @@ static int ft245r_send_and_discard(const PROGRAMMER *pgm, unsigned char *buf, si
 
 static int ft245r_recv(const PROGRAMMER *pgm, unsigned char *buf, size_t len) {
   ft245r_flush(pgm);
+  my.tx.len = 0;
   ft245r_fill(pgm);
 
 #if FT245R_DEBUG
@@ -289,9 +292,8 @@ static int ft245r_recv(const PROGRAMMER *pgm, unsigned char *buf, size_t len) {
   while(my.rx.discard > 0) {
     int result = ft245r_rx_buf_fill_and_get(pgm);
 
-    if(result < 0) {
+    if(result < 0)
       return result;
-    }
 
     --my.rx.discard;
   }
@@ -299,17 +301,17 @@ static int ft245r_recv(const PROGRAMMER *pgm, unsigned char *buf, size_t len) {
   for(size_t i = 0; i < len; ++i) {
     int result = ft245r_rx_buf_fill_and_get(pgm);
 
-    if(result < 0) {
+    if(result < 0)
       return result;
-    }
 
     buf[i] = (uint8_t) result;
+#if FT245R_BITBANG_VARIABLE_PULSE_WIDTH_WORKAROUND
     for(int j = 1; j < baud_multiplier; ++j) {
       result = ft245r_rx_buf_fill_and_get(pgm);
-      if(result < 0) {
+      if(result < 0)
         return result;
-      }
     }
+#endif
   }
   return 0;
 }
@@ -333,6 +335,7 @@ static int ft245r_drain(const PROGRAMMER *pgm, int display) {
 // Ensure any pending writes are sent to the FTDI chip before sleeping
 static void ft245r_usleep(const PROGRAMMER *pgm, useconds_t usec) {
   ft245r_flush(pgm);
+  my.tx.len = 0;
   usleep(usec);
 }
 
@@ -388,6 +391,7 @@ static int get_pin(const PROGRAMMER *pgm, int pinname) {
   uint8_t byte;
 
   ft245r_flush(pgm);
+  my.tx.len = 0;
 
   if(ftdi_read_pins(my.handle, &byte) != 0)
     return -1;
@@ -629,9 +633,8 @@ static inline unsigned char extract_data(const PROGRAMMER *pgm, unsigned char *b
 
   buf += offset*(8*FT245R_CYCLES);
   for(j = 0; j < 8; j++) {
-    if(GET_BITS_0(buf[buf_pos], pgm, PIN_AVR_SDI)) {
+    if(GET_BITS_0(buf[buf_pos], pgm, PIN_AVR_SDI))
       r |= bit;
-    }
     buf_pos += FT245R_CYCLES;
     bit >>= 1;
   }
@@ -649,9 +652,8 @@ static inline unsigned char extract_data_out(const PROGRAMMER *pgm, unsigned cha
 
   buf += offset*(8*FT245R_CYCLES);
   for(j = 0; j < 8; j++) {
-    if(GET_BITS_0(buf[buf_pos], pgm, PIN_AVR_SDO)) {
+    if(GET_BITS_0(buf[buf_pos], pgm, PIN_AVR_SDO))
       r |= bit;
-    }
     buf_pos += FT245R_CYCLES;
     bit >>= 1;
   }
@@ -668,9 +670,8 @@ static int ft245r_cmd(const PROGRAMMER *pgm, const unsigned char *cmd, unsigned
   unsigned char buf[128];
 
   buf_pos = 0;
-  for(i = 0; i < 4; i++) {
+  for(i = 0; i < 4; i++)
     buf_pos += set_data(pgm, buf + buf_pos, cmd[i]);
-  }
   buf[buf_pos] = 0;
   buf_pos++;
 
@@ -836,9 +837,8 @@ static int ft245r_open(PROGRAMMER *pgm, const char *port) {
       char *endptr = NULL;
 
       devnum = strtol(startptr, &endptr, 10);
-      if((startptr == endptr) || (*endptr != '\0')) {
+      if((startptr == endptr) || (*endptr != '\0'))
         devnum = -1;
-      }
       pmsg_notice2("%s(): device number parsed as: %d\n", __func__, devnum);
     }
   }
@@ -904,9 +904,8 @@ static int ft245r_open(PROGRAMMER *pgm, const char *port) {
   }
 
   rv = ft245r_set_bitclock(pgm);
-  if(rv) {
+  if(rv)
     goto cleanup;
-  }
 
   // Drain any extraneous input
   ft245r_drain(pgm, 0);
@@ -993,9 +992,8 @@ static int do_request(const PROGRAMMER *pgm, const AVRMEM *m) {
   my.req_pool = p;
 
   ft245r_recv(pgm, buf, bytes);
-  for(j = 0; j < n; j++) {
+  for(j = 0; j < n; j++)
     m->buf[addr++] = extract_data(pgm, buf, (j*4 + 3));
-  }
   return 1;
 }
 
diff --git a/src/urbootautogen.c b/src/urbootautogen.c
index ba6fb5e8..0420a1e0 100644
--- a/src/urbootautogen.c
+++ b/src/urbootautogen.c
@@ -166,18 +166,18 @@ static const struct {
 };
 
 
-# define _ok(c) ((c) && (uint8_t) (c) <= 0x7f)
+#define _ok(c) ((c) > 0 && (c) < 0x7f)
 
 // Is s a ^[0-9]+k[0-9]+$ pattern for baud rate?
 static int is_baudrate_k(const char *s) {
   int pre=0, post=0;
 
-  while(_ok(*s) && isdigit(*s))
+  while(_ok(*s) && isdigit((int) *s))
     pre++, s++;
   if(*s != 'k')
     return 0;
   s++;
-  while(_ok(*s) && isdigit(*s))
+  while(_ok(*s) && isdigit((int) *s))
     post++, s++;
   return !*s && pre && post;
 }
@@ -217,12 +217,12 @@ static int is_fcpu_m(const char *s) {
 
   if(is_fcpu_type(*s))
     s++;
-  while(_ok(*s) && isdigit(*s))
+  while(_ok(*s) && isdigit((int) *s))
     pre++, s++;
   if(*s != 'm')
     return 0;
   s++;
-  while(_ok(*s) && isdigit(*s))
+  while(_ok(*s) && isdigit((int) *s))
     post++, s++;
   return !*s && pre && post;
 }
@@ -239,11 +239,11 @@ static int is_num_unit(const char *s, const char *unit) {
 
   while(*s == '+')              // Ignore leading + (used as fillers for sorting)
     s++;
-  while(_ok(*s) && isdigit(*s))
+  while(_ok(*s) && isdigit((int) *s))
     pre++, s++;
   if(*s == '.')
     s++;
-  while(_ok(*s) && isdigit(*s))
+  while(_ok(*s) && isdigit((int) *s))
     post++, s++;
   if(!pre && !post)
     return 0;
@@ -252,12 +252,12 @@ static int is_num_unit(const char *s, const char *unit) {
     s++;
     if(*s == '-' || *s == '+')
       s++;
-    while(_ok(*s) && isdigit(*s))
+    while(_ok(*s) && isdigit((int) *s))
       ee++, s++;
     if(!ee)
       return 0;
   }
-  while(_ok(*s) && isspace(*s))
+  while(_ok(*s) && isspace((int) *s))
     s++;
 
   size_t ulen = strlen(unit);
diff --git a/src/urbootlist.c b/src/urbootlist.c
index d42c77eb..1b414bf3 100644
--- a/src/urbootlist.c
+++ b/src/urbootlist.c
@@ -9,8 +9,8 @@
  * Published under GNU General Public License, version 3 (GPL-3.0)
  * Meta-author Stefan Rueger <stefan.rueger@urclocks.com>
  *
- * v 1.2
- * 29.04.2025
+ * v 1.21
+ * 18.05.2025
  *
  */
 
@@ -260398,7 +260398,7 @@ static uint16_t *ul_urtemplate(const uint64_t *bl) {
       hn = 0;
     }
     // Move 1 bit from Huffman bootloader bit string to a single Huffman code variable
-    hc = (hc<<1) | (h64 & 1), hcn++;
+    hc = ((uint64_t) hc << 1) | (h64 & 1), hcn++;
     h64 >>= 1, hn++;
     if(hcn > 27) {
       pmsg_error("unexpected problem decoding bootloader code");
@@ -260519,7 +260519,7 @@ static int blcmp(const void *v1, const void *v2) {
 }
 
 int urbootexists(const char *mcu, const char *io, const char *blt, int req_feats) {
-  size_t m, i, b, c;
+  int m, i, b, c;
 
   for(m=0; m<UL_MCU_N; m++)
     if(str_eq(mcus[m], mcu))
@@ -260553,7 +260553,7 @@ int urbootexists(const char *mcu, const char *io, const char *blt, int req_feats
 Urboot_template **urboottemplate(const Avrintel *up, const char *mcu, const char *io, const char *blt,
   int req_feats, int req_ulevel, int showall, int *np) {
 
-  size_t m, i, b, c, req_c, n = -1U;
+  int m, i, b;
   Urboot_template **ret = NULL;
 
   for(m=0; m<UL_MCU_N; m++)
@@ -260576,14 +260576,14 @@ Urboot_template **urboottemplate(const Avrintel *up, const char *mcu, const char
 
   if(req_feats < 0 || req_feats >= (int) (sizeof urfeat/sizeof*urfeat))
     Return("unexpected feature request");
-  req_c = urfeat[req_feats];
+  int req_c = urfeat[req_feats];
   // Specific feature set chosen? Then only one bootloader needs decoding and requesting
   int spec = !showall && (req_ulevel == 0 || req_ulevel == 4) ;
 
   ret = mmt_malloc(sizeof *ret * UL_CONFIG_N);
   *np = 0;
 
-  for(c = 0; c < UL_CONFIG_N; c++) {
+  for(int c = 0; c < UL_CONFIG_N; c++) {
     if(!spec || c == req_c) {
       const char *cfg = configs[c];
 
@@ -260608,7 +260608,8 @@ Urboot_template **urboottemplate(const Avrintel *up, const char *mcu, const char
         goto error;
 
       ret[*np] = mmt_malloc(sizeof **ret);
-      ret[n = (*np)++]->tofree = ut;
+      int n = (*np)++;
+      ret[n]->tofree = ut;
 
       int size = ut[0];         // Bootloader size including 6-byte-table in top flash
       int usage = ut[1];        // Flash usage, ie, boot section size or multiple of flash pages