tools: use byte padding to skip unused register ranges

This simplifies the code. The fields are blank anyway so there is no way
to access them anyway (volatile or not).
Also do some other related simplifications of the code that result from
this change.

tools/gen-device-svd/gen-device-svd.go

@@ -668,8 +668,7 @@ var (
 			}
 
 			var regType string
-			eSize := register.elementSize
+			switch register.elementSize {
-			switch eSize {
 			case 4:
 				regType = "volatile.Register32"
 			case 2:
@@ -677,27 +676,16 @@ var (
 			case 1:
 				regType = "volatile.Register8"
 			default:
-				eSize = 4
 				regType = "volatile.Register32"
 			}
 
 			// insert padding, if needed
 			if address < register.address {
 				bytesNeeded := register.address - address
-				switch bytesNeeded {
+				if bytesNeeded == 1 {
-				case 1:
+					w.WriteString("\t_ byte\n")
-					w.WriteString("\t_ volatile.Register8\n")
-				case 2:
-					w.WriteString("\t_ volatile.Register16\n")
-				case 3:
-					w.WriteString("\t_ [3]volatile.Register8\n")
-				default:
-					numSkip := (register.address - address) / uint64(eSize)
-					if numSkip == 1 {
-						fmt.Fprintf(w, "\t_ %s\n", regType)
 				} else {
-						fmt.Fprintf(w, "\t_ [%d]%s\n", numSkip, regType)
+					fmt.Fprintf(w, "\t_ [%d]byte\n", bytesNeeded)
-					}
 				}
 				address = register.address
 			}
@@ -707,9 +695,8 @@ var (
 				// This is a cluster, not a register. Create the cluster type.
 				regType = "struct {\n"
 				subaddress := register.address
-				var subregSize uint64
-				var subregType string
 				for _, subregister := range register.registers {
+					var subregType string
 					switch subregister.elementSize {
 					case 4:
 						subregType = "volatile.Register32"
@@ -728,21 +715,13 @@ var (
 					if subaddress != subregister.address {
 						bytesNeeded := subregister.address - subaddress
 						if bytesNeeded == 1 {
-							regType += "\t\t_ volatile.Register8\n"
+							regType += "\t\t_ byte\n"
-						} else if bytesNeeded == 2 {
-							regType += "\t\t_ volatile.Register16\n"
 						} else {
-							numSkip := (subregister.address - subaddress)
+							regType += fmt.Sprintf("\t\t_ [%d]byte\n", bytesNeeded)
-							if numSkip < 1 {
-								continue
-							} else if numSkip == 1 {
-								regType += "\t\t_ volatile.Register8\n"
-							} else {
-								regType += fmt.Sprintf("\t\t_ [%d]volatile.Register8\n", numSkip)
-							}
 						}
 						subaddress += bytesNeeded
 					}
+					var subregSize uint64
 					if subregister.array != -1 {
 						subregSize = uint64(subregister.array * subregister.elementSize)
 					} else {
@@ -753,11 +732,11 @@ var (
 				}
 				if register.array != -1 {
 					if subaddress != register.address+uint64(register.elementSize) {
-						numSkip := ((register.address + uint64(register.elementSize)) - subaddress) / subregSize
+						bytesNeeded := (register.address + uint64(register.elementSize)) - subaddress
-						if numSkip <= 1 {
+						if bytesNeeded == 1 {
-							regType += fmt.Sprintf("\t\t_ %s\n", subregType)
+							regType += "\t_ byte\n"
 						} else {
-							regType += fmt.Sprintf("\t\t_ [%d]%s\n", numSkip, subregType)
+							regType += fmt.Sprintf("\t_ [%d]byte\n", bytesNeeded)
 						}
 					}
 				} else {