Improve comments

src/avr.c

@@ -1254,7 +1254,7 @@ int avr_mem_bitmask(const AVRPART *p, const AVRMEM *mem, int addr) {
   return bitmask;
 }
 
-// Bitmask for ISP programming (classic parts only)
+// Bitmask for verification after ISP programming (classic parts only)
 static uint8_t get_fuse_bitmask(const AVRMEM *m) {
   int ret = 0xFF;
 

src/avrcache.c

@@ -76,7 +76,7 @@
  * avr_chip_erase_cached() erases the chip and discards pending writes() to
  * flash or EEPROM. It presets the flash cache to all 0xff alleviating the
  * need to read from the device flash. However, if the programmer serves
- * bootloaders is_spm(pgm) then the flash cache is reset
+ * bootloaders, recognised by is_spm(pgm), then the flash cache is reset
  * instead, necessitating flash memory be fetched from the device on first
  * read; the reason for this is that bootloaders emulate chip erase and they
  * won't overwrite themselves (some bootloaders, eg, optiboot ignore chip
@@ -142,6 +142,7 @@ int avr_has_paged_load(const PROGRAMMER *pgm, const AVRPART *p, const AVRMEM *me
     mem->size > 0 && mem->size%mem->page_size == 0 && mem_is_paged_type(mem) && !(p && avr_mem_exclude(pgm, p, mem));
 }
 
+// Sanity only: guard against a user setting pgm->xyz_byte to avr_xyz_read_byte_cached (AVRDUDE doesn't)
 #define fallback_read_byte (pgm->read_byte != avr_read_byte_cached? led_read_byte: avr_read_byte_default)
 #define fallback_write_byte (pgm->write_byte != avr_write_byte_cached? led_write_byte: avr_write_byte_default)
 

src/update.c

@@ -529,7 +529,7 @@ static int update_avr_write(const PROGRAMMER *pgm, const AVRPART *p, const AVRME
 
   if(rc < 0)
     return -1;
-  // @@@ has there has been output in the meantime to make the ", x bytes written" look out of place?
+  // @@@ has there been output in the meantime to make the ", x bytes written" look out of place?
   if(pbar && !(flags & UF_VERIFY))
     pmsg_info("%d byte%s of %s written", fs.nbytes, str_plural(fs.nbytes), m_name);
   else if(!pbar)