Zero all memories when initializing program

[emu8051.git] / src / psw.c

diff --git a/src/psw.c b/src/psw.c
index 4dd2a67..09352ad 100644 (file)
--- a/src/psw.c
+++ b/src/psw.c
@@ -22,98 +22,116 @@
 #include "reg8051.h"
 #include "memory.h"
 
+/* Returns 0 or 1 */
+int
+psw_read_bit(int bit)
+{
+       return (memory_read8(INT_MEM_ID, _PSW_) >> bit) & 0x01;
+}
+
 void
-psw_write_cy(int cy)
+psw_write_bit(int bit, int val)
 {
        u_int8_t psw = memory_read8(INT_MEM_ID, _PSW_);
 
-       if (cy)
-               psw |= PSW_FLAG_CY;  /* Set */
+       if (val)
+               psw |= (1 << bit);  /* Set */
        else
-               psw &= ~PSW_FLAG_CY; /* Clear */
+               psw &= ~(1 << bit); /* Clear */
 
        memory_write8(INT_MEM_ID, _PSW_, psw); /* Save updated value */
 }
 
+/* Returns 0 or 1 */
+int
+psw_read_cy(void)
+{
+       return psw_read_bit(PSW_BIT_CY);
+}
+
+void
+psw_write_cy(int cy)
+{
+       psw_write_bit(PSW_BIT_CY, cy);
+}
+
 void
 psw_set_cy(void)
 {
-       psw_write_cy(1);
+       psw_write_bit(PSW_BIT_CY, 1);
 }
 
 void
 psw_clr_cy(void)
 {
-       psw_write_cy(0);
+       psw_write_bit(PSW_BIT_CY, 0);
 }
 
 /* Returns 0 or 1 */
 int
-psw_read_cy(void)
+psw_read_ac(void)
 {
-       return memory_read8(INT_MEM_ID, _PSW_) >> PSW_BIT_CY;
+       return psw_read_bit(PSW_BIT_AC);
 }
 
 void
 psw_write_ac(int ac)
 {
-       u_int8_t psw = memory_read8(INT_MEM_ID, _PSW_);
-
-       if (ac)
-               psw |= PSW_FLAG_AC;  /* Set */
-       else
-               psw &= ~PSW_FLAG_AC; /* Clear */
-
-       memory_write8(INT_MEM_ID, _PSW_, psw); /* Save updated value */
+       psw_write_bit(PSW_BIT_AC, ac);
 }
 
 void
 psw_set_ac(void)
 {
-       psw_write_ac(1);
+       psw_write_bit(PSW_BIT_AC, 1);
 }
 
 void
 psw_clr_ac(void)
 {
-       psw_write_ac(0);
+       psw_write_bit(PSW_BIT_AC, 0);
 }
 
 /* Returns 0 or 1 */
 int
-psw_read_ac(void)
+psw_read_ov(void)
 {
-       return memory_read8(INT_MEM_ID, _PSW_) >> PSW_BIT_AC;
+       return psw_read_bit(PSW_BIT_OV);
 }
 
 void
 psw_write_ov(int ov)
 {
-       u_int8_t psw = memory_read8(INT_MEM_ID, _PSW_);
-
-       if (ov)
-               psw |= PSW_FLAG_OV;  /* Set */
-       else
-               psw &= ~PSW_FLAG_OV; /* Clear */
-
-       memory_write8(INT_MEM_ID, _PSW_, psw); /* Save updated value */
+       psw_write_bit(PSW_BIT_OV, ov);
 }
 
 void
 psw_set_ov(void)
 {
-       psw_write_ov(1);
+       psw_write_bit(PSW_BIT_OV, 1);
 }
 
 void
 psw_clr_ov(void)
 {
-       psw_write_ov(0);
+       psw_write_bit(PSW_BIT_OV, 0);
 }
 
-/* Returns 0 or 1 */
-int
-psw_read_ov(void)
+/*
+ * Compute parity of bits in accumulator:
+ *   parity = 0: even number of ones in accumulator
+ *   parity = 1: odd  number of ones in accumulator
+ */
+void
+psw_compute_parity_bit(void)
 {
-       return memory_read8(INT_MEM_ID, _PSW_) >> PSW_BIT_OV;
+       int parity = 0;
+       uint8_t acc = memory_read8(INT_MEM_ID, _ACC_);
+
+       while (acc) {
+               parity = !parity;
+               acc = acc & (acc - 1);
+       }
+
+       psw_write_bit(PSW_BIT_P, parity);
 }