semihosting: Add support for SYS_ELAPSED/SYS_TICKFREQ as milliseconds

src/target/semihosting.c

@@ -703,6 +703,20 @@ int32_t semihosting_time(target_s *const target)
 #endif
 }
 
+int32_t semihosting_elapsed(target_s *const target, const semihosting_s *const request)
+{
+ /* Extract where the write should occur to */
+ const target_addr_t block_taddr = request->r1;
+ /*
+ * Acquire platform ticks (even if uint32_t ATM).
+ * BMP: SysTicks. This is faster (on-probe) than talking to GDB.
+ * BMDA: gettimeofday() as milliseconds.
+ */
+ const uint64_t elapsed = platform_time_ms();
+ /* Write the elapsed ticks to the target as a pair of uint32_t in LE order per ABI */
+ return target_mem32_write(target, block_taddr, &elapsed, sizeof(elapsed)) ? -1 : 0;
+}
+
 int32_t semihosting_readc(target_s *const target)
 {
  /* Define space for a character */
@@ -860,9 +874,13 @@ int32_t semihosting_handle_request(target_s *const target, const semihosting_s *
  case SEMIHOSTING_SYS_TMPNAM:
  return semihosting_temp_name(target, request);
 
- // not implemented yet:
- case SEMIHOSTING_SYS_ELAPSED: /* elapsed */
- case SEMIHOSTING_SYS_TICKFREQ: /* tickfreq */
+ case SEMIHOSTING_SYS_ELAPSED:
+ return semihosting_elapsed(target, request);
+
+ case SEMIHOSTING_SYS_TICKFREQ:
+ /* 1000 Hz SysTick, or BMDA "precision". Servicing breakpoints over SWD is not fast. */
+ return SYSTICKHZ;
+
  default:
  return -1;
  }