qemu-4.2.0/hw/misc/mac_via.c: 2 * bad test ?

[dcb]

1.

qemu-4.2.0/hw/misc/mac_via.c:417:27: style: Expression is always false because 'else if' condition matches previous condition at line 412. [multiCondition]

                } else if ((m->data_out & 0xf3) == 0xa1) {
...
                } else if ((m->data_out & 0xf3) == 0xa1) {

2.

qemu-4.2.0/hw/misc/mac_via.c:467:27: style: Expression is always false because 'else if' condition matches previous condition at line 463. [multiCondition]

Duplicate.

[dcb (dcb314)]

gcc compiler flag -Wduplicated-cond will catch this kind of problem.

You might want to switch it on in your builds. It has been available for over a year.

[Philippe Mathieu-Daudé (philmd)]

On 12/16/19 12:58 PM, dcb wrote:
> gcc compiler flag -Wduplicated-cond will catch this kind of problem.

Interesting, thanks for sharing!

>
> You might want to switch it on in your builds. It has been available for
> over a year.
>

[Philippe Mathieu-Daudé (philmd)]

This code seems to emulate a RTC device connected via I2C to the VIA chipset.

This might be the expected code (simply looking at this file, without checking the datasheet):
-- >8 --
--- a/hw/misc/mac_via.c
+++ b/hw/misc/mac_via.c
@@ -409,7 +409,7 @@ static void via1_rtc_update(MacVIAState *m)
                 } else if (m->data_out == 0x8d) { /* seconds register 3 */
                     m->data_in = (time >> 24) & 0xff;
                     m->data_in_cnt = 8;
- } else if ((m->data_out & 0xf3) == 0xa1) {
+ } else if ((m->data_out & 0xf3) == 0xa3) {
                     /* PRAM address 0x10 -> 0x13 */
                     int addr = (m->data_out >> 2) & 0x03;
                     m->data_in = v1s->PRAM[addr];
@@ -460,7 +460,7 @@ static void via1_rtc_update(MacVIAState *m)
                 } else if (m->cmd == 0x35) {
                     /* Write Protect register */
                     m->wprotect = m->data_out & 1;
- } else if ((m->cmd & 0xf3) == 0xa1) {
+ } else if ((m->cmd & 0xf3) == 0xa3) {
                     /* PRAM address 0x10 -> 0x13 */
                     int addr = (m->cmd >> 2) & 0x03;
                     v1s->PRAM[addr] = m->data_out;
---

This file won a "/* TODO port to I2CBus */" comment :)

[Laurent Vivier (laurent-vivier)]

I think VIA RTC access method has been implemented earlier (Classic Mac, 1984-1989) than the I2C specification, so I'm not sure we can/should port this to an I2C bus.

Specs are (from Apple Macintosh Family Hardware Reference Chapter 2, Classi Macitosh Processor and Control)

z0000001 Seconds register 0 (lowest-order byte)
z0000101 Seconds register 1
z0001001 Seconds register 2
z0001101 Seconds register 3 (highest-order byte)
00110001 Test register (write-only)
00110101 Write-Protect Register (write-only)
z010aa01 RAM address 100aa ($10-$13) (first 20 bytes only)
z1aaaa01 RAM address 0aaaa ($00-$0F) (first 20 bytes only)
z0111aaa Extended memory designator and sector number
          (Macintohs 512K enhanced and Macintosh plus only)

For a read request, z=1, for a write z=0
The letter a indicates bits whose value depend on what parameter RAM byte you want to address

So I think the mask/values should be:

diff --git a/hw/misc/mac_via.c b/hw/misc/mac_via.c
index f3f130ad96cc..7402cf3f1ee8 100644
--- a/hw/misc/mac_via.c
+++ b/hw/misc/mac_via.c
@@ -414,7 +414,7 @@ static void via1_rtc_update(MacVIAState *m)
                     int addr = (m->data_out >> 2) & 0x03;
                     m->data_in = v1s->PRAM[addr];
                     m->data_in_cnt = 8;
- } else if ((m->data_out & 0xf3) == 0xa1) {
+ } else if ((m->data_out & 0xc3) == 0xc1) {
                     /* PRAM address 0x00 -> 0x0f */
                     int addr = (m->data_out >> 2) & 0x0f;
                     m->data_in = v1s->PRAM[addr];
@@ -460,11 +460,11 @@ static void via1_rtc_update(MacVIAState *m)
                 } else if (m->cmd == 0x35) {
                     /* Write Protect register */
                     m->wprotect = m->data_out & 1;
- } else if ((m->cmd & 0xf3) == 0xa1) {
+ } else if ((m->cmd & 0xf3) == 0x21) {
                     /* PRAM address 0x10 -> 0x13 */
                     int addr = (m->cmd >> 2) & 0x03;
                     v1s->PRAM[addr] = m->data_out;
- } else if ((m->cmd & 0xf3) == 0xa1) {
+ } else if ((m->cmd & 0xc3) == 0x41) {
                     /* PRAM address 0x00 -> 0x0f */
                     int addr = (m->cmd >> 2) & 0x0f;
                     v1s->PRAM[addr] = m->data_out;

[Philippe Mathieu-Daudé (philmd)]

Patch posted: https://<email address hidden>/msg666836.html

[Laurent Vivier (laurent-vivier)]

Fixed here:
https://git.qemu.org/?p=qemu.git;a=commitdiff;h=b2619c158ab5