Add support for resistance-derived current

This commit adds support for configuring the current requested from the
power supply in the form of a resistance.  This is useful for powering
resistive loads when a voltage range is configured.

lib/include/pd.h

  * W: watt
  * CW: centiwatt
  * MW: milliwatt
+ *
+ * O: ohm
+ * CO: centiohm
+ * MO: milliohm
  */
 #define PD_MV2PRV(mv) ((mv) / 20)
 #define PD_MV2PDV(mv) ((mv) / 50)
 #define PD_PDV2MV(pdv) ((pdv) * 50)
 #define PD_PAV2MV(pav) ((pav) * 100)
 
+#define PD_MA2CA(ma) (((ma) + 10 - 1) / 10)
 #define PD_MA2PDI(ma) (((ma) + 10 - 1) / 10)
 #define PD_MA2PAI(ma) (((ma) + 50 - 1) / 50)
 #define PD_CA2PAI(ca) (((ca) + 5 - 1) / 5)
 
 #define PD_MW2CW(mw) ((mw) / 10)
 
+#define PD_MO2CO(mo) ((mo) / 10)
+
 /* Get portions of a voltage in more normal units */
 #define PD_MV_V(mv) ((mv) / 1000)
 #define PD_MV_MV(mv) ((mv) % 1000)
 #define PD_CW_W(cw) ((cw) / 100)
 #define PD_CW_CW(cw) ((cw) % 100)
 
+/* Get portions of a resistance in more normal units */
+#define PD_CO_O(co) ((co) / 100)
+#define PD_CO_CO(co) ((co) % 100)
+
 /*
  * Unit constants
  */
 
 #define PD_MA_MIN 0
 #define PD_MA_MAX 5000
+#define PD_CA_MIN PD_MA2CA(PD_MA_MIN)
+#define PD_CA_MAX PD_MA2CA(PD_MA_MAX)
 #define PD_PDI_MIN PD_MA2PDI(PD_MA_MIN)
 #define PD_PDI_MAX PD_MA2PDI(PD_MA_MAX)
 
 #define PD_MW_MIN 0
 #define PD_MW_MAX 100000
 
+#define PD_MO_MIN 500
+#define PD_MO_MAX 655350
+
 
 #endif /* PDB_PD_H */

src/config.c

         case PDBS_CONFIG_FLAGS_CURRENT_DEFN_P:
             chprintf(chp, "p: %d.%02d W\r\n", PD_CW_W(cfg->p), PD_CW_CW(cfg->p));
             break;
+        case PDBS_CONFIG_FLAGS_CURRENT_DEFN_R:
+            chprintf(chp, "r: %d.%02d \316\251\r\n", PD_CO_O(cfg->r), PD_CO_CO(cfg->r));
+            break;
     }
 }
 

src/device_policy_manager.c

             return scfg->i;
         case PDBS_CONFIG_FLAGS_CURRENT_DEFN_P:
             return (scfg->p * 1000 + mv - 1) / mv;
+        case PDBS_CONFIG_FLAGS_CURRENT_DEFN_R:
+            return (mv * 10 + scfg->r - 1) / scfg->r;
+        default:
+            /* In the case of an error, return a current that can't be
+             * requested. */
+            return PD_CA_MAX + 1;
     }
 }
 

src/shell.c

     }
 }
 
+static void cmd_set_r(BaseSequentialStream *chp, int argc, char *argv[])
+{
+    if (argc != 1) {
+        chprintf(chp, "Usage: set_r power_in_m\316\251\r\n");
+        return;
+    }
+
+    char *endptr;
+    long i = strtol(argv[0], &endptr, 0);
+    if (i >= PD_MO_MIN && i <= PD_MO_MAX && endptr > argv[0]) {
+        /* Convert mohms to the unit used in the configuration object */
+        tmpcfg.r = PD_MO2CO(i);
+        /* Set the flags to say we're storing a resistance */
+        tmpcfg.flags &= ~PDBS_CONFIG_FLAGS_CURRENT_DEFN;
+        tmpcfg.flags |= PDBS_CONFIG_FLAGS_CURRENT_DEFN_R;
+    } else {
+        chprintf(chp, "Invalid resistance\r\n");
+        return;
+    }
+}
+
 static void cmd_output(BaseSequentialStream *chp, int argc, char *argv[])
 {
     if (argc == 0) {
     {"set_vrange", cmd_set_vrange, "Set the minimum and maximum voltage in millivolts"},
     {"set_i", cmd_set_i, "Set the current in milliamps"},
     {"set_p", cmd_set_p, "Set the power in milliwatts"},
+    {"set_r", cmd_set_r, "Set the resistance in milliohms"},
     {"output", cmd_output, "Get or set the output status"},
     {"get_source_cap", cmd_get_source_cap, "Print the capabilities of the PD source"},
     {NULL, NULL, NULL}